23:11 "and you probably save more money saving your tires than saving a tiny bit of fuel" I fully agree you there! Tires are so expensive that having extra tire wear is not worth only a slight improvement in the fuel economy.
Imo, that heavily depends You should run proper pressures anyways But at 50-60€ per tire and projected 25.000km longevity even like 0.1L/100km is gonna be worth more than that
Interesting video. I think at 60 and above air drag is by far the biggest factor in fuel consumption which may explain less of a difference with the reduced pressures.
Yes. drag is a very big factor. However lower pressures also result in lower stance on the road and ground effect which may also create lower drag. Interesting stuff.
Same here. Always keep in mind the accuracy of the pump or pressure reading device, air temperature inside the tyres and outside temperature. When warm, the air inside the tyres will expand, so keep that in mind as well.
Overinflation can be bad, just hope you don't have a lot of weight in the car or regularly drive on rough terrain. The maximum PSI just before over inflation is better.
@@rufusgreenleaf2466 not really as they are within the upper limits of the manufacturer recommendation. Tyres can take way more pressure then you'd imagine
Nice job as always! I think I might have an idea of another variable that's affecting the results. The higher the pressure in the tires, the more the tire will expand. If the overall diameter of the tires changes, the speedometer and odometer will be affected just like if you change the tire size. If the tires are expanded more, the speedometer and odometer will read artificially low because the tires will move the car more distance per turn, throwing off your results since the computer will think you covered less distance than you actually did and at a higher than actual speed, giving worse results. Lowering the pressures will have the opposite effect, making the speedometer and odometer read artificially higher, giving better results. Also, it makes sense to me that tire pressure would make more at difference at lower speeds since the rolling resistance is a larger part of the total power requirement at low speeds due to dramatically less aerodynamic drag. Rolling resistance increases linearly with speed (double your speed and power required to overcome rolling resistance doubles) while aerodynamic drag increases exponentially (double your speed and the power required to overcome the aerodynamic drag quadruples). This is the main reason for reduced efficiency at high speeds. At 20 MPH, aerodynamic drag is pretty low, so rolling resistance is likely the largest resistance the engine has to overcome. At 40-60 MPH, aerodynamic drag will be much more significant.
Theres a negligible difference, I changed my tires from 225/35/R18 to 235/60/R18 and the onboard computer gives the same results as a manual calculation on most of them (same as with oem tires)
Před rokem
I thought rolling resistance was v² and air resistance v⁴, but oh well, the point remains the same
@ No, both predominantly square law. There are higher order components, but the coefficients are very low, so only start making a difference at very high speeds (fast jet aircraft type speeds).
Your content is exactly what experiment lovers need like me and I don't understand how bigger youtube channels that are official orgs and even sell magazines for car stats and performance do not conduct these kind of low cost experiments that are way more telling sometimes than the ones made in the car labs. I believe they lack that real spark of interest in cars that people like you and us have, so they don't care defying what experts say works and test some of the theories that seem common knowledge but are more greyish in reality. Like the video that you made about fuel economy almost any experienced driver including me thought that if you have a very high gear uphill at very low revs it would be less fuel effective than a lower gear at maybe 1400 rpm which proved not true with your testing. You are the myth busters show, but exclusively for cars and with way more useful experiments that are applicable to the day to day life of an average driver.
I did math. Results in percentages: -17% change to recommended tyre pressure saw a 3.7% increase in fuel consumption at 40mph, and 0.8% increase in fuel consumption at 60mph. +17% change to recommended tyre pressure saw a 2.4% decrease in fuel consumption at 40mph, and 5.2% decrease in fuel consumption at 60mph.
Or like all the stupid BMW drivers, a roof box or ski rack. During lockdown there seemed to be a sale on ski racks and every BMW I saw had them fitted - even though they could not fly out of the country and nowhere was open to ski in the UK. The funniest roof box setup I saw was on a Volvo estate car - the car was empty, but it would have been possible to fit another car inside the back. I'm not sure why people drive about with them on as not many use them, is it some fashion accessory or BMW and AUDI drivers showing they are even more stupid than everyone else? It's always the same make that attracts the same type of people, maybe because they are really easy cars to drive, so people that are not very good tend to go for the models with driver assist packs and automatic gearboxes leaving them a stop and go pedal and big thing for pointing the car.
You always seem to go to loads of effort! I can never wrap my head around the difference in recommended pressures, even with the same size wheel/tyre. Mine are supposed to be 36 on the front and 32 on the back but I just put them on 38 all round. After watching this I’ll probably let a bit out and see how it goes. Thank you again!
It seems to be pretty common for front wheel drive cars to use higher pressures in the front, due to the mass of the engine and drivetrain being at the front. Keep an eye on the wear patterns on the tyres: if they're overinflated, you'll likely see more wear in the middle.
I've literally just checked my tyre pressures today and topped them up and then this video popped up. I passed just over a month ago but will always be watching your videos, they are so helpful 👍🚘
Higher pressure in tires is only an option if your commute consists only of good roads. If roads are bad and/or you go on unpaved or even off road sometimes overpressure tires would eventually cause damage to your rims and suspension, so any fuel savings will be nullified. Tires are in fact part of your suspension and has been calculated by vehicle engineers with normal pressure in mind.
Great video but I cant help but wonder about two things that I didn't catch anywhere. First would be that you didn't mention your tyre/rim size. Narrow tyre with high sidewall will have different variation of rolling resistance with different pressures than a wider but lower tyre. I am sure that getting multiple sets of differently sized tyres just for the experiment would not be worth it but it seems that this detail should be mentioned just for better overview of what kind of tyre you are specifically talking about. My second point is that all cars that I encountered so far have always had pressure recommended for "comfort" and "economy". I think it would be also informative to include this into the comparison (both Skoda and VW do this so I would say Seat has to as well) apart from simply lowering the pressures by a flat amount since those two numbers will be what most people would use. Anyway thanks for the great content, cant wait for the next one.
@@ConquerDriving My last 3 cars all had Normal/Comfort, ECO and full load. Petrol and diesels. ECO was 39psi, comfort/normal (up to 3 people) was 33psi and full load was about 44psi. Nothing about 4/5 people and full load. When i picked the cars up from new they all had 39psi, each time i lowered it to 33psi the garage put it back to 39psi stating tyres were underinflated on the service! 33psi is OK, I used to get 55mpg in a diesel in town, but with a petrol get 33mpg, so very disappointing. The diesel went because the DPF kept blocking despite motorway runs (after 10,000miles) and the dealership set the car to regenerate every 300miles which caused more errors and wasted fuel, also caused more servicing and replacement of glowplugs etc. 39PSI does make the petrol car "bounce" and I every bump and lines on the road, it also feels better cornering at speed - but I never drive it to that extent, it can also mean more suspension damage over uneven roads with holes in as the tyre can't flex and absorb some impact, so you get a harsh thud. At 39psi it is more likely to just burst compared to 33psi. There is NO difference to fuel economy between 33psi and 39psi in any petrol or diesel i have driven over the last 15years. I still get the same readings. That is with different sized tyres on the cars. The only safety difference is that 39PSI can prevent aquaplaning as experienced on motorways, this is due to less of the tyre being in contact with the road. If you run through standing water with 33PSI that tyre works so hard to displace all the water and can't. 39PSI alters the shape and contact and is more effective. Try it in heavy rain.
One thing I can think of is when running much lower pressures, you reduce your effective wheel diameter, causing your car to think it's driven more miles than it actually has. Thus the higher fuel economy readings at lower pressure I'm curious to test by measuring out a set distance with a pedometer, and comparing it with elapsed miles on the car.
Maybe if you alter the tire pressure you also change the diameter of the tires. your ecu has no way to detect this so the distance you travel is off and so is the mpg from your tripcomputer.
Hi Richard, thanks for all the effort you put into the video, I especially like that you listed your fuel mileage figures in multiple units, which should cover every country out there. I am in the US and have been driving since 1971. I have always been interested in fuel mileage. Cars in the US have the manufacturer recommended tire pressures purposely set low to improve ride comfort. All cars here have power assisted steering so, the increased steering effort due to low tire pressures would go unnoticed. I set my air pressure for each tire based upon the weight the tire is carrying. I select the pressure such that the contact weight across the face of the tire is constant. This method gives good fuel mileage and maximizes tire wear. I also do my own front end alignments. With a front drive car in the US, the tire pressures usually work out to 42 to 44 psi front, 28 to 34 rear. The rear pressure variation is due to the number of people normally carried and stuff in the boot. To give a little more accurate results with your mileage versus tire pressure tests, may I suggest instead to do a coasting test. To make things easier, just take the car up to 20 mph, then measure the coasting distance.
I love how you still put that end bit in there even though you were wrong. Now we know that if we're getting un-even wear, we could possibly check to see whether there is another version of our car which weighs a different amount but still has the same recommended tire pressure. Could help quite a few people out.
@@ConquerDriving Ah alright, didn't realize you mentioned it earlier on. Regardless, was a good touch, especially for someone like me who's currently in the market for a new car. Thanks for all the effort you put into your videos :)
This is why a lot of people put 2PSI lower than stated in and as they drive, the pressure will increase to what is shown on the handbook after a few minutes. I am not sure that is the correct way to do it.
@@Bond2025 Not sure it would be appropriate in that the manufacturer might have already accounted for this. It would be nice to know if one way or the other.
this is really helpful for those who want to save as much fuel as possible. As a cyclist also, higher tire pressure yields much lighter load on the pedals to maintain.
Interesting test. I usually have about 5 psi above the factory spec because I like the small change in handling and if it also improves economy, it's fine. (The handling is a bit more accurate thanks to less tire rubber flexing but it might be a bit more noisy.)
Lowering tyre pressures on a wheel, causes the wheel to be literally smaller, therefore the L/100 or mpg will read better because the car thinks you're travelling a certain X distance, where in fact the car travelled less in the real world, voiding the results. I loved the video and love your interest and dedication. If all else is equal, this is the last piece to the puzzle.
Respect for the time that went into this test! I'd say don't trust the car trip computer, you can't be too sure what kind of logic is going on behind it, and if the reset is a true reset each time. Especially can't trust the ECU on a VW group vehicle! Personally I overinflate the tyres by 5-10 psi on our cars, the way I see it is that the pressure is always escaping out of the tyres at some rate anyway, so prefer to have a bit extra. Plus, in our Suzuki Swift owners manual, there are separate economy pressures that are something ridiculous like 45psi on a 16 inch wheel - point is, it's safe to go 5-10psi over!
Thanks Richard, this was a really interesting video and can imagine you put a lot of time and effort prepping and filming it. The Leon manufacturer pressures of 29/26 seem quite low compared to other cars - I wonder if its down to the larger sportier tyres?
Tyre width plays a big part for tyre pressure. There's a reason a 70kg bicycle+cyclist run their tyres at 80-120PSI. If there's more contact area of the tyre on the road there's more Square inches touching the ground. If you have 10"² of contact then 30psi would exert 300 pounds of pressure... If the contact patch was 1"² then it would only exert 30 pounds of pressure before deforming in the example of a tyre (a racing bicycle with 30psi would probably ground out onto the rim as soon as you sat on it) I was actually quite surprised to find space saver tyres actually use more fuel... I can imagine most of that is down to lack of tyre development for that rim size though. I know they recommend around 60psi though, which I can imagine means that a space saver is more like to have lost air pressure when you actually need it.
Your car is impressively economical, I must say! I should consider something like it for a daily - my current daily does ~10l/100km in the city and my project car is a lot worse at ~15l/100km.. getting to 4-6l/100km would be a definite savings.
The manufacturer's recommended tyre pressures take into account handling and grip in both straight line and curved line driving, wet and dry, breaking and accelerating. They do not only look at fuel consumption and tyre wear to arrive at their recommendations.
If you carry heavy loads increase those pressures a lot, it's only UK spec cars which are recommended 29/26 psi, rest of World is 32/29 psi for that tyre size. I only mention it as I noticed you have an Extra Load tyre on the rear (94 load rating compared to 91 load rating as standard), and Extra Load tyres need slightly more pressure than a standard load tyre to carry the same weight. Bear in mind the Ecomotive versions run a factory 39/39psi for fuel saving, and yes they will wear in the middle! I get a fair few more miles out of Extra Load tyres, I'd imagine you would too for the work your car does, the carcass is stronger but does have a trade off with worse comfort. One important thing to note with under inflation is the amount the tyre deflects, at motorway speeds it creates a huge amount of heat in the tyre and that's the blowout cause almost always. We all know to not mix tyre size on the same axle, but don't mix load ratings either. You could have tried a coast test with different pressures, might work might not.
Should've done +10psi as well! 😛 And I can't believe how low the tyre pressure on your car is. I've never seen that low. And I hope you haven't done your wheel alignment at Halfords!!! 🥴
My Toyota Aygo recommends 32PSI all round... I always run them at 40PSI as I find the wear is more even, at 32PSI the shoulders of the tyres wear quicker then the inside. At 40PSI the wear is even all the way down to the point I replace them.
Some explanation for why higher speeds are less impacted by lower tire pressure: Lower tire pressure is supposed to reduce your mpg because there is a larger contact patch with the ground, which increases friction, and more importantly because the tire has to flex and distort at the bottom as it squishes. At higher speeds, the tire isn't fully recovering from that distortion/displacement. At higher speeds, the tire is spinning quickly enough that it hits an equilibrium state where the tire is no longer actively squishing at the bottom. Also, at higher speeds, centrifugal force pulls the tire outward, stretching it, further reducing the effects of that squishing.
A variable affecting results could actually be the air conditioner as its load will vary depending on how hard it works, on the hwy my fuel economy gauge will change depending on whether the aircon is switched on or not
Deviating from the Manufacturers recommended pressures by more than 10% could lead to a fine, and points on the licence. In an RTA the insurance company will wriggle to avoid paying out. One of the major reasons for tyre failure on main roads is underinflation , they overheat and blow. Check the pressures and tread depth frequently, they are all that stick you to the road, and always fit the best tyres you can afford.
Well said, in accident investigations the first thing police start with is taking tyre pressures. The insurance company will also refuse to pay out if they can prove you did not follow the manufacturers guidelines for operating the vehicle and maintaining it. People have been prosecuted over incorrect tyre inflation.
The build-in cruise control is probably based on RPM and might change with tire pressure. GPS speed might give different results. The build-in consumption calculation might also be based on distance calculated using wheel spins and might change with tire pressure.
Man... I love my car, it's an old Mitubishi Galant, but seeing your fuel consumption makes my shed a tear every time. You seem to be around 4-6L/100km... My 150 PS engine meanwhile gulps down 8-9L/100km. Its kind of impressive how much more efficient cars have gotten between 1999 and 2014. But I'm gonna stick to that car for as long as possible anyway, even if I'm paying a hefty price in gas. Makes these videos all the more important for me^^
The difference probably gets larger in city driving, because I assume starting and stopping with lower tire pressure is going to have a big impact on fuel economy.
its best to follow recommendations with a tiny twist. If you expect heavy hauling, add one or two PSI more. Only if you go to sand/gravel or ice, lower your pressure a bit, but never more than 10% unless you know what you are doing.
If I can add another note, modern cars have thinner and stiffer sidewalls, compared to older cars with high sidewalls. With larger 4wd tires like a 265/75/R15, low tire pressures (below 20psi) at high speeds can generate a lot of heat, damaging the tire. It's the sidewalls that hold the car up. The more it is allowed to flex the more heat is generated. Same for the tread, more contact, more heat. This thermal energy isn't just created, it's converted from additional effort made by the car's engine to turn the wheel.
Generally; maintaining recommended tyre pressure (or pressure where tyres wear even) is what one needs to aim for. Raised pressure may throw measurements off (as detailed below), reduce grip (less surface to contact), and ruin ride comfort. Lower pressure may just as well be as bad. Only positive effect is an increase in surface, an increase in grip - under normal road use, it might come in handy under icy conditions, where slush, snow and mud mixed is making traction and grip fade. A few PSIs of pressure difference won't harm, but under- and overinflation can wear suspension elements out. That is one tradeoff to keep in mind. (Also, I need to do my research on wide tyres. What I know probably apply more prominently to narrower ones...) While notable, I don't expect fuel economy to change radically due to pressure changes - unless severe.
Low tire pressure in nearly every case reduces grip on hard surfaces due to an increase in slip angle, which is the same reason racing tires are slicks as they have near zero slip angle. Factory recommended pressures are always on the 'soft' side for ride comfort and will compromise tire life and handling as a trade-off. Air those tires up unless you're interested in off-road performance where soft tires are much preferred, or if you want a softer ride.
35 psi front and rear in my Peugeot 306 turbo diesel. I have 17 inch alloys instead of the original 14 inch steel wheels, now running 205/40 profile tyres instead of the previous 185/65 ones. I get a consistent 53mpg, in spite of having increased the fuelling a bit, to complement a freer intake and exhaust. When bog standard, the best I ever got was 47mpg, even at the recommended tyre pressures. Modern cars are so much heavier, safety etc., and I think that most of the loss of economy must be due to actually getting a car off the mark and rolling. A 6 speed gearbox would suit me well, were I one for doing long distance driving, but I rarely go further than round trips of 12 miles nowadays. Isn't it strange how cars of yesteryear, motorbikes also, had much lower recommended tyre pressures ? Heavy 1960's and 1970's cars were often under 30psi and a Triumph 750cc bike I had was 26 front, 28 rear. My lighter, i.e., plastic adorned 2004 1000cc Suzuki V twin is 36 front, 42 rear. Too high, in my opinion, for a 9 stoner like myself. That said, the rear wears its centre out pretty rapidly if I drop the pressure by more than a couple of psi. There's no way we can win ! The VAT man is the only one continually grinning.
Oh dear, another clueless boy racer! Who do you trust more - a company that spends millions on research and development, or a backstreet trader that makes wild claims in order to take your money? The best parts for the car are fitted when you buy it and you're not going to turn a 1.2 or 1.4 or 1.6 in to a racing car. 1. Increased fuelling. Absolute rubbish, you can't as the ECU stops this, so it doesn't matter what you think you are doing to the car or even what you try, it will still go back to what it should be based on the dynamic adjustment from sensor readings. Fuel rail pressures can be messed with using a cheap nasty "tuning box" often costing £400 even though it contains a simple voltage multiplier costing 23p! Those devices take NO input from the ECU or send info back, all they do is increase fuel pressure by a set amount. They go in series with the fuel rail and damage the engine, especially when cold and more diesel is sent in, the box causes even more to go in and causes smoke and clattering. You would need a proper ECU REMAP and who would you trust doing that? Some youtuber that just increases everything from standard without any real knowledge. Don't forget, those companies will never pay up if you damage your engine! It is also possible to insurance and police investigators to find evidence of using such devices as that info can not be deleted from the ECU - it is accessed in investigations all the time. Manufacturers also refuse to honour warranty claims and you void your insurance anyway. 2. The air intake! Biggest way to make money from fools is to sell them a tiny mesh/oil or foam filter that doesn't even filter and is a much smaller surface area than a paper filter, so ends up blocking up and degrading performance far quicker, plus it doesn't pass anywhere near the amount of filtered air to the engine. There is also a sales opportunity for cleaning solutions, you will have to clean it every few months. If you had a paper filter it could still pass more filtered air until it was nearly blocked. People will remove resonators due to not knowing what they do, they cancel out noise on the intake, they do not restrict anything. The pipes and inlet are the correct size and the standard system fitted to cars passes more air than the engine requires at full RPM. 3. The exhaust, another way to get money from gullible fools. You can spend what you like and it will make NO difference to performance. All it will do is make the car sound rubbish and everyone will look around thinking someone is driving with a hole in their exhaust and see a small car doing 20mph. 4. Suspension. Don't just throw kits on without getting the suspension geometry checked or you upset the handing. People are so clueless they call a DAMPER a shock absorber. The shock absorber on a car is the SPRING itself, the DAMPER is what keeps the wheel/tyre in contact with the road. Lowered suspension is bad on a family car as it can make handling unpredictable and is often the cause of many accidents. Lowering a ride height might look nice, but does nothing for handling. Many boy racers grow out of it after being scammed for years. Many feel stupid after spending all that money for years and having a car that is slower and noisier than standard, plus costs more to insure and the handling is rubbish. Use the VW approach and fit a fake engine noise generator - in the Golf it has a thing called a SOUNDAKTOR under the bonnet to make the occupants hear the noise of a V8. Switch that off and the Golf sounds like any other car inside!
PLEASE DO A DRIVING RANT!! Would be very interesting to know a professional driving instructors perspective and what you’d have to say about people in the overtaking lanes doing 15 under!
Staggeringly useful video Richard 👍👍. What it highlights to me is 'recommended' is simply best guess. No one at SEAT will have dtiven 193,000 in the car but you have, therefore you (as an knowledgeable enthusiasti) are in a better postion to suggest which tyre pressure suits your requirements.
They would have tested tyre wear but it all depends on the use of the car, so it isn’t possible to have a perfect recommended pressure for all scenarios. For example, if the car is driven on roads with more corners, it would be expected that less wear occurs in the centre compared to the outside of the tyre.
I was thinking there would be diminishing returns above 40 psi, so not much point going 50, 60, 70 other than having a harder ride and less grip on loose surfaces. I'm not sure at which point the centre of the tyre balloons out, but radial tyres seem to maintain an even diameter over a wider range of pressures and most of the contact patch decrease is front to back, which is the direction that reduces rolling resistance the most. I think going slightly higher than normal is best for grip as it stabilises the sidewalls. So if you're driving around on 20 psi it's about time you got the air pump out!
I believe I can explain the MPG results you're seeing, with slightly reduced pressures at low speed the vertical displacement of the car is less and so you use less energy. It's like having over inflated tyres on a mountain bike while biking a rough trail, the bouncing about wastes energy. The faster you go though the more you skip over the bumps and so the displacement is lessened. When driving faster centripal acceleration within the tyre itself will compensate for the pressure loss to some degree as the tyre tries to lift away from the wheel.
PSI is best measured cold. the heat of the tire heats the air and softens the rubber changing the pressure. the only real way to test this is to let the ties cool then adjust pressure than heat the motor up than run the MPG test. But this 5 pound doesn't make a difference. In a large truck the difference between 90 psi and 120 only gains about 0.25- 0.5 on vehicles that get 6 or 7 MPG so its getting you about 5-10% better mpg to have 33% more air in the tire (tires are rated to up to 120 but only 90 is need to carry the weight) This make a big difference when you drive 400 to 700 miles in one day. not so much when you drive that in a month. DO NOT EXCEED THE MAX PRESSURE RATING OF YOUR TIRE as you drive the tire heats up and this can cause the tire to explode when driven @ high speed or long distances. The max pressure recommended by the car manufacture is less important than the one by the tire maker. Higher strength tires can support higher pressure and will often require it to keep the proper shape.
Just bought a vauxhall mokka the suggested eco setting on the door sticker is 39 front 41 rear thought thats gonna be too high so I had set them to 36 as a compromise the ride was so bumpy on bumpy roads even at 36 it must be awful at 39 lowered them now to the lowest 32 psi setting its improved the ride a lot. Not gonna bother chasing fuel economy with the pressures the suspension is stiff and short wheelbase doesnt help. I may set them higher for long journeys but around town a lot the bumpy potholes and speedbumps are awful in this car dont buy one if your looking for comfort even got one with leather seats but they are only comfortable when parked when driving the suspension is bad on this car
Coincidence this video coming out. I had to top my front tyres up last Wednesday, i checked them and they were at 21psi when they should have been between 30 and 33. They looked a little down but i didn't expect that much.
Fantastic video and explanation! Super detailes and helpful. I have to agree wirh the findings. My Audi recommends lower tures pressure for comfort which I find the ride softer and comfortable. Regarding fuel economy in the comfort pressure, I am getting the the as on normal pressure with better ride quality. I guese it's all about experimenting.
If you also factor in the economy of different tyre types/brands, they add up. For instance the difference between a tyre that has a rating of E at fuel economy versus a tyre that has a C fuel economy rating would be ~0.2 l/100km. So add that to the economy of +0.3 bar and you get roughly around 0.3-0.4-0.5 l/100km. That is quite the improvement.
@@ConquerDriving Heck, with a chip tune you might even drop another 10% off the fuel consumption. I drive a Golf Mk7 and i have an average of 5l/100km. If i get 10% off that would be around 4.5l/100km, add more efficient tyres and run them with a slightly higher pressure and i might drop my average fuel consumption to a 4.2-4.4. Marginal gains, but they sure do add up.
HANG ON! the cars trip computer is working out mpg by using fuel used vs distance travelled. Its working distance travelled by rotation of the tire not GPS. Therefore the lower tire pressure is being helped by the tire circumstance being reduced as it is squashed. So the car thinks it's travelled further!
That's a good point but it is a tiny difference in diameter. I would like to measure it but I don't think I can measure the wheels with that level of accuracy.
instead of driving at same speed you should drive at same RPM. Lower pressure gives smaller diameter of the wheel and your speed will not match, what means you could be driving slower than you think. Slower drive means less consumption. One more thing, due to inertia to keep car moving requires low amount of energy, but empty tires will make most of the difference on stop and go kind of drive where you need a lot of energy to do drastic change in motion. But whole point of correct tire pressure is tire grip and wear.
Before watching this video, let me guess the answer: "it depends", "please follow manufacturer guidelines" and "check tire pressure regularly". My pre-watch guess at the video contents: higher pressure will usually lead to less rolling resistance, which means less wasted power. Running on nearly flat tires will have high rolling resistance. However, overfilling your tires will cause to uneven wear and a loss of grip as well as potential blow-out issues; underfilling your tires can help a lot with grip but will cause abnormal wear can cause the tire wall to crack, as well as resulting in difficulty keeping the car stable through even slight corners. Also, any fuel savings you might hope to get for overfilling your tire are likely to be marginal at best. Find out the correct pressure for your car/tire/wheel combination and use that. Pressure will fluctuate with temperature, so you need to keep checking pressure as ambient temperature changes.
I imagine that optimal tire pressure falls along a bell curve. So if you put your PSI at the optimal, then as you drive it will only go downhill and will require more frequent upkeep to stay optimal. For the average (lazy) car owner, manufacturers may over state the recommended tire pressure so that over the period between upkeep the tire improves a bit and then decreases. Sort of doubling the time someone needs to wait before adding air to their tires.
There is a website that provides the correct tyre pressures. All you need to do is input the car registration number and it gives you the results. I recently bought a new Ford Kuga St-Line X and the website matched the psi that the car had when I purchased it. 32 at the front and 33 at the back.
Hello Richard! Thank you for always making these great and insightful videos that we can't get anywhere else! I know I speak for many of your subscribers when I say I really value your first principles approach to driving and the assumptions people have about cars and related topics. I'm curious to hear your thoughts about the idea of warming up the engine before starting to drive? Is this really beneficial from a fuel economy (or engine health) perspective? And how does this hold for petrol vs diesel cars? Thanks a lot in advance!
Thank you for watching. Everyone has their own opinion about warming up the engine before driving. My advice is to let it run for 5 to 10 seconds and then get moving, letting it warm up at idle will only use more fuel. But drive gently until it's up to temperature to help protect the engine.
10:02 maybe the wheels spin fast enough to overcome the resistance of the road due to more optimal momentum at 60 mph as opposed to 40mph, where the momentum is lower , making the tires work harder for every spin.
Serious Question: Don't you teach a "Schulterblick", like a quick glance over your shoulder, before changing lanes or turning in the uk? Over here its check center mirror, side mirror, signal, do a look over your shoulder, move the steering wheel. if you miss the view over your shoulder once or twice in your driving test you can fail easily.
I check tire pressure about weekly or when there are temperature changes of 10 degress C Last week we had 22-25°C Today more like 10-13°C Had to pump another 0.2bar into the tyres
Doesn't over inflating tyres have less grip and therefore a slight safety concern. A feet or two in braking distance may mean the difference between being involved in an accident or not.
Maybe at higher tyre pressures the circumference of the tyre is larger, so you're actually traveling faster at "20"mph? And the the opposite for the lower pressure, So at "20"mph you're actually travelling slower? I suppose you could check the footage and see if there's a time differential between starting and finishing the test? At higher speeds this circumference difference could the counteracted by centrifugal force?
Tire manufacturer says 35psi, my door panel says 28psi on my 79 Lincoln. I've compromised at 29psi to keep the ride quality high, which is the point of a luxury car. But I've always worried about how it affects economy and most importantly, tire wear.
tire pressure should be set firstly by tire manufacturer recommendations, not car manufacturer secondly, should be adjusted to the weather you drive in car manufacturer pressure recommendations are for the tires it leaves the factory on
There are two major factors which I would consider caused the lower fuel consumption of your car with lower tyre pressures - Fist is reduced windage due to the car being slightly lower to the ground which allows the better aerodynamics of under the car (ground effect) and lower effective frontal area. The other maybe less important factors may be the tyre characteristics themselves including tread and sidewall for those particular tyres.
I am kind of surprised to see that at higher speeds and lower pressures, the gas mileage loss is so slim. In hindsight it makes kind of sense, as at 60 mph the tire should expierience enough centrifugal force that the rubber expands to a point where it almost matches the diameter it would have under recommended pressures (decreasing its formerly raised contact patch and rolling resistance to almost a normal level, negating the mileage losses) If that is true, it would also explain the lower mileage at 40 mph where the tires are exposed to less than half the centrifugal force so they cant quite strech enough and the rolling resistance remains higher than under normal conditions. [The 20 mph results are quite a mystery to me so take the following with a Brick of salt: The results might be due to an everslightly smaller wheel diameter causing misreadings in the cars speed. The sensor at the axle/wheel only reports the amount of wheel rotations to the car, while ignoring the actual diameter of the wheel (which is smaller now due to lower pressures) so one might as well be travelling at 18 or 19 mph instead of 20 mph making the engine work easier and therefore burn that little bit less fuel.]
The confusing thing is that at 20mph there is very little wind resistance. 40mph might be more affected by tyre pressures than 60mph because at 60mph the rolling resistance plays a smaller factor in economy than the wind resistance.
It is possible that the lower pressure does in fact have lower rolling resistance. Lots of variable here. Isn't the point of the scientific method to confront our preconceptions with data? Just because you don't know why something isn't happening it doesn't mean that it isn't happening. Perhaps more accurate measurement equipment would give absolute confidence in the results. In the bicycle world experiments have found that on rougher surfaces lower tire pressure reduce rolling resistance because there is less vibration transmitted to vehicle and vibration is basically vertical motion, which is an acceleration of the vehicle is a non-forward direction. It takes energy to accelerate that mass up and down (vibration).
Overinflated, wear on the inside; underinflated, wear on the outside, that I understand. But I've seen tire wears on alternate columns, like after a drive, the tire surface becomes striped, like dark-light-dark-light-dark. I wonder what caused that.
If someone has TMPS in their car, can you tell how much tyre pressure rise is monitored during city and highway drives and also mention the outside temperature.
Tyres lose about 1 PSI in the winter every month maybe 1.5 or 2 depending how cold it is. I always put my 69 plate Corolla to 38 PSI on all 4 when it was recommended at 36 and I get real good mpg on the road. Regularly at 45 to 70 mpg
The Corolla Hybrid gets exceptional fuel economy. Assuming you have the hybrid as they did sell a small petrol in the GB when the latest Corolla was released.
Sometimes tyre pressure can also alter wheel alignment, causing more tyre scrub with higher pressure. I can feel the steering get a bit hard if I increase or reduce the pressure a lot. Would be interesting to see the results on an alignment machine with the various tyre pressures.
Suspension geometry has nothing to do with tyre pressures! Tyre pressure relates to how much air is in a tyre, not how a wheel is aligned. Two different things.
Price of fuel has sky-rocketed now....Our Rav4 Hybrid is achieving well over 61 mpg (imp) on a trgular basis. We run our tyres at 38 psi. With fuel being over $2 a litre every cent counts.
We areaactually well under the tyre manufacturers max pressures......The vehicle manufacturers pressure recommendations for tyre pressure seems to be about comfort and less noise
That's a good point, it would change a tiny bit. Lower pressures would mean you aren't going slower than recorded and higher pressures would be faster than recorded. The wheels will be spinning at the same speed but the wind resistance will be a tiny bit different. I doubt the difference will be noticed because I would guess it's less than 1mph difference.
@@ConquerDriving Effective rolling distance of the tyres changes with pressure. At lower pressures the effective rolling distance of each tyre per rev is reduced. This is how cars can tell if one tyre is reducing in pressure, it rotates more than the other tyres. So without checking the recorded milage of each of your runs you are not getting the true mpg as the car will think it has gone further with low pressures and a shorter distance at higher pressures. The effect of this is that if with lower tyre pressures you reduce your recorded mpg by 1% you may be going an actual distance of 101% of recorded distance and the two balance out. The mpg calculation in the car's computer is assuming the tyres are at normal running pressure and have the normal running distance per revolution.
I remember, years ago, watching a video where they had a camera set up to look at the tyres while driving. The higher the speed, the less the tyres were actually in contact with the road. I guess that could explain the 60mph figures.
the commitment needed to do this videos are actually insane, nice job nice videos👍
And for adding all the stats/measurements for speed and pressures, etc.. Helps for a lot of us
Your Seat Leon has been an absolute trooper, love that car so much, hope it still rock for a long time more.
In recent months this channel is evolving amazingly in terms of content we would like to watch and learn
23:11 "and you probably save more money saving your tires than saving a tiny bit of fuel"
I fully agree you there! Tires are so expensive that having extra tire wear is not worth only a slight improvement in the fuel economy.
Imo, that heavily depends
You should run proper pressures anyways
But at 50-60€ per tire and projected 25.000km longevity even like 0.1L/100km is gonna be worth more than that
Interesting video.
I think at 60 and above air drag is by far the biggest factor in fuel consumption which may explain less of a difference with the reduced pressures.
Yes. drag is a very big factor. However lower pressures also result in lower stance on the road and ground effect which may also create lower drag. Interesting stuff.
@@Rob-fx2dw Lol
Would centripetal force making the tyre "expand" affect the results?
Great video idea! I always tend to keep mine slightly overinflated at the upper recommendations of the vehicle manufacture
Same here. Always keep in mind the accuracy of the pump or pressure reading device, air temperature inside the tyres and outside temperature. When warm, the air inside the tyres will expand, so keep that in mind as well.
Overinflation can be bad, just hope you don't have a lot of weight in the car or regularly drive on rough terrain. The maximum PSI just before over inflation is better.
@@rufusgreenleaf2466 if carrying more weight then the manufacturer recommends even more inflation
@@uk7866 Regardless you said you over inflate your tyres which could cause uneven tyre damage and risk a blow out. Just be careful is all i say.
@@rufusgreenleaf2466 not really as they are within the upper limits of the manufacturer recommendation. Tyres can take way more pressure then you'd imagine
Nice job as always! I think I might have an idea of another variable that's affecting the results. The higher the pressure in the tires, the more the tire will expand. If the overall diameter of the tires changes, the speedometer and odometer will be affected just like if you change the tire size. If the tires are expanded more, the speedometer and odometer will read artificially low because the tires will move the car more distance per turn, throwing off your results since the computer will think you covered less distance than you actually did and at a higher than actual speed, giving worse results. Lowering the pressures will have the opposite effect, making the speedometer and odometer read artificially higher, giving better results.
Also, it makes sense to me that tire pressure would make more at difference at lower speeds since the rolling resistance is a larger part of the total power requirement at low speeds due to dramatically less aerodynamic drag. Rolling resistance increases linearly with speed (double your speed and power required to overcome rolling resistance doubles) while aerodynamic drag increases exponentially (double your speed and the power required to overcome the aerodynamic drag quadruples). This is the main reason for reduced efficiency at high speeds. At 20 MPH, aerodynamic drag is pretty low, so rolling resistance is likely the largest resistance the engine has to overcome. At 40-60 MPH, aerodynamic drag will be much more significant.
Very good points!
Theres a negligible difference, I changed my tires from 225/35/R18 to 235/60/R18 and the onboard computer gives the same results as a manual calculation on most of them (same as with oem tires)
I thought rolling resistance was v² and air resistance v⁴, but oh well, the point remains the same
@ No, both predominantly square law. There are higher order components, but the coefficients are very low, so only start making a difference at very high speeds (fast jet aircraft type speeds).
Your content is exactly what experiment lovers need like me and I don't understand how bigger youtube channels that are official orgs and even sell magazines for car stats and performance do not conduct these kind of low cost experiments that are way more telling sometimes than the ones made in the car labs. I believe they lack that real spark of interest in cars that people like you and us have, so they don't care defying what experts say works and test some of the theories that seem common knowledge but are more greyish in reality. Like the video that you made about fuel economy almost any experienced driver including me thought that if you have a very high gear uphill at very low revs it would be less fuel effective than a lower gear at maybe 1400 rpm which proved not true with your testing. You are the myth busters show, but exclusively for cars and with way more useful experiments that are applicable to the day to day life of an average driver.
I did math. Results in percentages:
-17% change to recommended tyre pressure saw a 3.7% increase in fuel consumption at 40mph, and 0.8% increase in fuel consumption at 60mph.
+17% change to recommended tyre pressure saw a 2.4% decrease in fuel consumption at 40mph, and 5.2% decrease in fuel consumption at 60mph.
The only logical thing next is to install the roof rack. :) Great video as always!
I was thinking of putting some weights in the car for another test. Depends how well this video does.
Or like all the stupid BMW drivers, a roof box or ski rack. During lockdown there seemed to be a sale on ski racks and every BMW I saw had them fitted - even though they could not fly out of the country and nowhere was open to ski in the UK.
The funniest roof box setup I saw was on a Volvo estate car - the car was empty, but it would have been possible to fit another car inside the back.
I'm not sure why people drive about with them on as not many use them, is it some fashion accessory or BMW and AUDI drivers showing they are even more stupid than everyone else? It's always the same make that attracts the same type of people, maybe because they are really easy cars to drive, so people that are not very good tend to go for the models with driver assist packs and automatic gearboxes leaving them a stop and go pedal and big thing for pointing the car.
You always seem to go to loads of effort! I can never wrap my head around the difference in recommended pressures, even with the same size wheel/tyre. Mine are supposed to be 36 on the front and 32 on the back but I just put them on 38 all round. After watching this I’ll probably let a bit out and see how it goes. Thank you again!
It seems to be pretty common for front wheel drive cars to use higher pressures in the front, due to the mass of the engine and drivetrain being at the front. Keep an eye on the wear patterns on the tyres: if they're overinflated, you'll likely see more wear in the middle.
I've literally just checked my tyre pressures today and topped them up and then this video popped up. I passed just over a month ago but will always be watching your videos, they are so helpful 👍🚘
Higher pressure in tires is only an option if your commute consists only of good roads. If roads are bad and/or you go on unpaved or even off road sometimes overpressure tires would eventually cause damage to your rims and suspension, so any fuel savings will be nullified. Tires are in fact part of your suspension and has been calculated by vehicle engineers with normal pressure in mind.
Loving these fuel economy videos. I appreciate that you do actual tests and not just recite some random information from the internet
Great video but I cant help but wonder about two things that I didn't catch anywhere. First would be that you didn't mention your tyre/rim size. Narrow tyre with high sidewall will have different variation of rolling resistance with different pressures than a wider but lower tyre. I am sure that getting multiple sets of differently sized tyres just for the experiment would not be worth it but it seems that this detail should be mentioned just for better overview of what kind of tyre you are specifically talking about. My second point is that all cars that I encountered so far have always had pressure recommended for "comfort" and "economy". I think it would be also informative to include this into the comparison (both Skoda and VW do this so I would say Seat has to as well) apart from simply lowering the pressures by a flat amount since those two numbers will be what most people would use. Anyway thanks for the great content, cant wait for the next one.
I have not seen comfort and eco tyre pressures in any owners manuals I have looked at. Might be a new thing.
@@ConquerDriving My last 3 cars all had Normal/Comfort, ECO and full load. Petrol and diesels. ECO was 39psi, comfort/normal (up to 3 people) was 33psi and full load was about 44psi. Nothing about 4/5 people and full load.
When i picked the cars up from new they all had 39psi, each time i lowered it to 33psi the garage put it back to 39psi stating tyres were underinflated on the service!
33psi is OK, I used to get 55mpg in a diesel in town, but with a petrol get 33mpg, so very disappointing. The diesel went because the DPF kept blocking despite motorway runs (after 10,000miles) and the dealership set the car to regenerate every 300miles which caused more errors and wasted fuel, also caused more servicing and replacement of glowplugs etc.
39PSI does make the petrol car "bounce" and I every bump and lines on the road, it also feels better cornering at speed - but I never drive it to that extent, it can also mean more suspension damage over uneven roads with holes in as the tyre can't flex and absorb some impact, so you get a harsh thud. At 39psi it is more likely to just burst compared to 33psi.
There is NO difference to fuel economy between 33psi and 39psi in any petrol or diesel i have driven over the last 15years.
I still get the same readings. That is with different sized tyres on the cars.
The only safety difference is that 39PSI can prevent aquaplaning as experienced on motorways, this is due to less of the tyre being in contact with the road. If you run through standing water with 33PSI that tyre works so hard to displace all the water and can't. 39PSI alters the shape and contact and is more effective. Try it in heavy rain.
One thing I can think of is when running much lower pressures, you reduce your effective wheel diameter, causing your car to think it's driven more miles than it actually has. Thus the higher fuel economy readings at lower pressure I'm curious to test by measuring out a set distance with a pedometer, and comparing it with elapsed miles on the car.
Maybe if you alter the tire pressure you also change the diameter of the tires. your ecu has no way to detect this so the distance you travel is off and so is the mpg from your tripcomputer.
The difference is so small it would be lost in tolerance levels.
Hi Richard, thanks for all the effort you put into the video, I especially like that you listed your fuel mileage figures in multiple units, which should cover every country out there.
I am in the US and have been driving since 1971. I have always been interested in fuel mileage. Cars in the US have the manufacturer recommended tire pressures purposely set low to improve ride comfort. All cars here have power assisted steering so, the increased steering effort due to low tire pressures would go unnoticed.
I set my air pressure for each tire based upon the weight the tire is carrying. I select the pressure such that the contact weight across the face of the tire is constant. This method gives good fuel mileage and maximizes tire wear. I also do my own front end alignments. With a front drive car in the US, the tire pressures usually work out to 42 to 44 psi front, 28 to 34 rear. The rear pressure variation is due to the number of people normally carried and stuff in the boot.
To give a little more accurate results with your mileage versus tire pressure tests, may I suggest instead to do a coasting test. To make things easier, just take the car up to 20 mph, then measure the coasting distance.
That's a very good idea.
Really appreciate how scientific you are with your tests. You definitely must be reconsidering yourself while doing this something though!
I love how you still put that end bit in there even though you were wrong. Now we know that if we're getting un-even wear, we could possibly check to see whether there is another version of our car which weighs a different amount but still has the same recommended tire pressure. Could help quite a few people out.
I had to put it in as I mentioned it in another part of the video. So I put it in and corrected myself so it made sense.
@@ConquerDriving Ah alright, didn't realize you mentioned it earlier on. Regardless, was a good touch, especially for someone like me who's currently in the market for a new car. Thanks for all the effort you put into your videos :)
Your videos are always great. Can’t wait for a 200k mile review of the car.
Another factor at higher speeds are resultant higher tyre temperatures which then pushes up tyre pressure that you have not reported on.
This is why a lot of people put 2PSI lower than stated in and as they drive, the pressure will increase to what is shown on the handbook after a few minutes. I am not sure that is the correct way to do it.
@@Bond2025 Not sure it would be appropriate in that the manufacturer might have already accounted for this. It would be nice to know if one way or the other.
this is really helpful for those who want to save as much fuel as possible. As a cyclist also, higher tire pressure yields much lighter load on the pedals to maintain.
What an absolute legend, thank you for doing the work we didn't want to, be we really ought
Interesting test. I usually have about 5 psi above the factory spec because I like the small change in handling and if it also improves economy, it's fine. (The handling is a bit more accurate thanks to less tire rubber flexing but it might be a bit more noisy.)
Lowering tyre pressures on a wheel, causes the wheel to be literally smaller, therefore the L/100 or mpg will read better because the car thinks you're travelling a certain X distance, where in fact the car travelled less in the real world, voiding the results. I loved the video and love your interest and dedication. If all else is equal, this is the last piece to the puzzle.
Respect for the time that went into this test! I'd say don't trust the car trip computer, you can't be too sure what kind of logic is going on behind it, and if the reset is a true reset each time. Especially can't trust the ECU on a VW group vehicle! Personally I overinflate the tyres by 5-10 psi on our cars, the way I see it is that the pressure is always escaping out of the tyres at some rate anyway, so prefer to have a bit extra. Plus, in our Suzuki Swift owners manual, there are separate economy pressures that are something ridiculous like 45psi on a 16 inch wheel - point is, it's safe to go 5-10psi over!
Thanks Richard, this was a really interesting video and can imagine you put a lot of time and effort prepping and filming it. The Leon manufacturer pressures of 29/26 seem quite low compared to other cars - I wonder if its down to the larger sportier tyres?
Tyre width plays a big part for tyre pressure. There's a reason a 70kg bicycle+cyclist run their tyres at 80-120PSI.
If there's more contact area of the tyre on the road there's more Square inches touching the ground. If you have 10"² of contact then 30psi would exert 300 pounds of pressure... If the contact patch was 1"² then it would only exert 30 pounds of pressure before deforming in the example of a tyre (a racing bicycle with 30psi would probably ground out onto the rim as soon as you sat on it)
I was actually quite surprised to find space saver tyres actually use more fuel... I can imagine most of that is down to lack of tyre development for that rim size though. I know they recommend around 60psi though, which I can imagine means that a space saver is more like to have lost air pressure when you actually need it.
Thank you, it's not a heavy car and has quite big-ish tyres for it's weight so I guess this is why it's needs lower pressures.
Your car is impressively economical, I must say! I should consider something like it for a daily - my current daily does ~10l/100km in the city and my project car is a lot worse at ~15l/100km.. getting to 4-6l/100km would be a definite savings.
The manufacturer's recommended tyre pressures take into account handling and grip in both straight line and curved line driving, wet and dry, breaking and accelerating. They do not only look at fuel consumption and tyre wear to arrive at their recommendations.
I didn't know that.
Yes they do, mine has Standard 33PSI , full load 44PSI and ECO 39PSI. They state clearly the 39PSI is for fuel economy.
Thank you for calculating the kpl, that's the only ratio I'm used to
If you carry heavy loads increase those pressures a lot, it's only UK spec cars which are recommended 29/26 psi, rest of World is 32/29 psi for that tyre size. I only mention it as I noticed you have an Extra Load tyre on the rear (94 load rating compared to 91 load rating as standard), and Extra Load tyres need slightly more pressure than a standard load tyre to carry the same weight. Bear in mind the Ecomotive versions run a factory 39/39psi for fuel saving, and yes they will wear in the middle! I get a fair few more miles out of Extra Load tyres, I'd imagine you would too for the work your car does, the carcass is stronger but does have a trade off with worse comfort. One important thing to note with under inflation is the amount the tyre deflects, at motorway speeds it creates a huge amount of heat in the tyre and that's the blowout cause almost always. We all know to not mix tyre size on the same axle, but don't mix load ratings either. You could have tried a coast test with different pressures, might work might not.
Should've done +10psi as well! 😛
And I can't believe how low the tyre pressure on your car is. I've never seen that low.
And I hope you haven't done your wheel alignment at Halfords!!! 🥴
My Toyota Aygo recommends 32PSI all round... I always run them at 40PSI as I find the wear is more even, at 32PSI the shoulders of the tyres wear quicker then the inside. At 40PSI the wear is even all the way down to the point I replace them.
The ideal pressure for wear seems to vary from tire to tire.
Some explanation for why higher speeds are less impacted by lower tire pressure:
Lower tire pressure is supposed to reduce your mpg because there is a larger contact patch with the ground, which increases friction, and more importantly because the tire has to flex and distort at the bottom as it squishes.
At higher speeds, the tire isn't fully recovering from that distortion/displacement. At higher speeds, the tire is spinning quickly enough that it hits an equilibrium state where the tire is no longer actively squishing at the bottom.
Also, at higher speeds, centrifugal force pulls the tire outward, stretching it, further reducing the effects of that squishing.
I think the higher speed also means air resistance is more of a factor than rolling resistance.
A variable affecting results could actually be the air conditioner as its load will vary depending on how hard it works, on the hwy my fuel economy gauge will change depending on whether the aircon is switched on or not
Deviating from the Manufacturers recommended pressures by more than 10% could lead to a fine, and points on the licence. In an RTA the insurance company will wriggle to avoid paying out. One of the major reasons for tyre failure on main roads is underinflation , they overheat and blow.
Check the pressures and tread depth frequently, they are all that stick you to the road, and always fit the best tyres you can afford.
Well said, in accident investigations the first thing police start with is taking tyre pressures. The insurance company will also refuse to pay out if they can prove you did not follow the manufacturers guidelines for operating the vehicle and maintaining it.
People have been prosecuted over incorrect tyre inflation.
The build-in cruise control is probably based on RPM and might change with tire pressure.
GPS speed might give different results.
The build-in consumption calculation might also be based on distance calculated using wheel spins and might change with tire pressure.
Just answered the question I've been Googling. 👌👌👌
You're making such a great ad for seat leons 😂 Seems like the most efficient, and actually good performant car for a cheap daily driver
Man... I love my car, it's an old Mitubishi Galant, but seeing your fuel consumption makes my shed a tear every time. You seem to be around 4-6L/100km... My 150 PS engine meanwhile gulps down 8-9L/100km. Its kind of impressive how much more efficient cars have gotten between 1999 and 2014. But I'm gonna stick to that car for as long as possible anyway, even if I'm paying a hefty price in gas. Makes these videos all the more important for me^^
By chance are you in Canada? I ask since you quote figures in metric plus you wrote "gas". Dual citizen Brit Canadian here.
@@ibs5080 nope, I'm in Germany, thus metric, and I just happen to be more used to American English
The difference probably gets larger in city driving, because I assume starting and stopping with lower tire pressure is going to have a big impact on fuel economy.
its best to follow recommendations with a tiny twist. If you expect heavy hauling, add one or two PSI more. Only if you go to sand/gravel or ice, lower your pressure a bit, but never more than 10% unless you know what you are doing.
14:57 Probably because tyres get hotter at higher speed at pressure actually goes up! 😜
I really like your test vids
If I can add another note, modern cars have thinner and stiffer sidewalls, compared to older cars with high sidewalls. With larger 4wd tires like a 265/75/R15, low tire pressures (below 20psi) at high speeds can generate a lot of heat, damaging the tire.
It's the sidewalls that hold the car up. The more it is allowed to flex the more heat is generated. Same for the tread, more contact, more heat. This thermal energy isn't just created, it's converted from additional effort made by the car's engine to turn the wheel.
Generally; maintaining recommended tyre pressure (or pressure where tyres wear even) is what one needs to aim for.
Raised pressure may throw measurements off (as detailed below), reduce grip (less surface to contact), and ruin ride comfort.
Lower pressure may just as well be as bad. Only positive effect is an increase in surface, an increase in grip - under normal road use, it might come in handy under icy conditions, where slush, snow and mud mixed is making traction and grip fade.
A few PSIs of pressure difference won't harm, but under- and overinflation can wear suspension elements out. That is one tradeoff to keep in mind.
(Also, I need to do my research on wide tyres. What I know probably apply more prominently to narrower ones...)
While notable, I don't expect fuel economy to change radically due to pressure changes - unless severe.
Low tire pressure in nearly every case reduces grip on hard surfaces due to an increase in slip angle, which is the same reason racing tires are slicks as they have near zero slip angle. Factory recommended pressures are always on the 'soft' side for ride comfort and will compromise tire life and handling as a trade-off. Air those tires up unless you're interested in off-road performance where soft tires are much preferred, or if you want a softer ride.
35 psi front and rear in my Peugeot 306 turbo diesel. I have 17 inch alloys instead of the original 14 inch steel wheels, now running 205/40 profile tyres instead of the previous 185/65 ones. I get a consistent 53mpg, in spite of having increased the fuelling a bit, to complement a freer intake and exhaust. When bog standard, the best I ever got was 47mpg, even at the recommended tyre pressures. Modern cars are so much heavier, safety etc., and I think that most of the loss of economy must be due to actually getting a car off the mark and rolling. A 6 speed gearbox would suit me well, were I one for doing long distance driving, but I rarely go further than round trips of 12 miles nowadays. Isn't it strange how cars of yesteryear, motorbikes also, had much lower recommended tyre pressures ? Heavy 1960's and 1970's cars were often under 30psi and a Triumph 750cc bike I had was 26 front, 28 rear. My lighter, i.e., plastic adorned 2004 1000cc Suzuki V twin is 36 front, 42 rear. Too high, in my opinion, for a 9 stoner like myself. That said, the rear wears its centre out pretty rapidly if I drop the pressure by more than a couple of psi. There's no way we can win ! The VAT man is the only one continually grinning.
Oh dear, another clueless boy racer! Who do you trust more - a company that spends millions on research and development, or a backstreet trader that makes wild claims in order to take your money? The best parts for the car are fitted when you buy it and you're not going to turn a 1.2 or 1.4 or 1.6 in to a racing car.
1. Increased fuelling. Absolute rubbish, you can't as the ECU stops this, so it doesn't matter what you think you are doing to the car or even what you try, it will still go back to what it should be based on the dynamic adjustment from sensor readings. Fuel rail pressures can be messed with using a cheap nasty "tuning box" often costing £400 even though it contains a simple voltage multiplier costing 23p! Those devices take NO input from the ECU or send info back, all they do is increase fuel pressure by a set amount. They go in series with the fuel rail and damage the engine, especially when cold and more diesel is sent in, the box causes even more to go in and causes smoke and clattering. You would need a proper ECU REMAP and who would you trust doing that? Some youtuber that just increases everything from standard without any real knowledge.
Don't forget, those companies will never pay up if you damage your engine! It is also possible to insurance and police investigators to find evidence of using such devices as that info can not be deleted from the ECU - it is accessed in investigations all the time.
Manufacturers also refuse to honour warranty claims and you void your insurance anyway.
2. The air intake! Biggest way to make money from fools is to sell them a tiny mesh/oil or foam filter that doesn't even filter and is a much smaller surface area than a paper filter, so ends up blocking up and degrading performance far quicker, plus it doesn't pass anywhere near the amount of filtered air to the engine. There is also a sales opportunity for cleaning solutions, you will have to clean it every few months. If you had a paper filter it could still pass more filtered air until it was nearly blocked. People will remove resonators due to not knowing what they do, they cancel out noise on the intake, they do not restrict anything. The pipes and inlet are the correct size and the standard system fitted to cars passes more air than the engine requires at full RPM.
3. The exhaust, another way to get money from gullible fools. You can spend what you like and it will make NO difference to performance. All it will do is make the car sound rubbish and everyone will look around thinking someone is driving with a hole in their exhaust and see a small car doing 20mph.
4. Suspension. Don't just throw kits on without getting the suspension geometry checked or you upset the handing. People are so clueless they call a DAMPER a shock absorber. The shock absorber on a car is the SPRING itself, the DAMPER is what keeps the wheel/tyre in contact with the road. Lowered suspension is bad on a family car as it can make handling unpredictable and is often the cause of many accidents. Lowering a ride height might look nice, but does nothing for handling.
Many boy racers grow out of it after being scammed for years. Many feel stupid after spending all that money for years and having a car that is slower and noisier than standard, plus costs more to insure and the handling is rubbish. Use the VW approach and fit a fake engine noise generator - in the Golf it has a thing called a SOUNDAKTOR under the bonnet to make the occupants hear the noise of a V8. Switch that off and the Golf sounds like any other car inside!
@@Bond2025 Thanks very much for the compliment, I'm 66 ! I trust the evidence of my own experimentation.
PLEASE DO A DRIVING RANT!!
Would be very interesting to know a professional driving instructors perspective and what you’d have to say about people in the overtaking lanes doing 15 under!
Most of the time I over inflate tyre by about 3 psi and refill tyre when pressure goes down by 3 psi below recommended pressure
Staggeringly useful video Richard 👍👍. What it highlights to me is 'recommended' is simply best guess. No one at SEAT will have dtiven 193,000 in the car but you have, therefore you (as an knowledgeable enthusiasti) are in a better postion to suggest which tyre pressure suits your requirements.
They would have tested tyre wear but it all depends on the use of the car, so it isn’t possible to have a perfect recommended pressure for all scenarios. For example, if the car is driven on roads with more corners, it would be expected that less wear occurs in the centre compared to the outside of the tyre.
Fantastic video. The dedication is real good job
God bless you for putting US system measurements
Great video. Maybe one day you should take leon to a track circuit. 4:42 gives a glimpse of what it's capable of achieving.
I have often thought that, but I have an MX5.
I was thinking there would be diminishing returns above 40 psi, so not much point going 50, 60, 70 other than having a harder ride and less grip on loose surfaces. I'm not sure at which point the centre of the tyre balloons out, but radial tyres seem to maintain an even diameter over a wider range of pressures and most of the contact patch decrease is front to back, which is the direction that reduces rolling resistance the most.
I think going slightly higher than normal is best for grip as it stabilises the sidewalls. So if you're driving around on 20 psi it's about time you got the air pump out!
Very informative video thanks for all your hard work making these videos
love these videos! your testing is incredible
Fantastic video explanations! Thank you very much Richard!
I believe I can explain the MPG results you're seeing, with slightly reduced pressures at low speed the vertical displacement of the car is less and so you use less energy. It's like having over inflated tyres on a mountain bike while biking a rough trail, the bouncing about wastes energy. The faster you go though the more you skip over the bumps and so the displacement is lessened. When driving faster centripal acceleration within the tyre itself will compensate for the pressure loss to some degree as the tyre tries to lift away from the wheel.
PSI is best measured cold. the heat of the tire heats the air and softens the rubber changing the pressure. the only real way to test this is to let the ties cool then adjust pressure than heat the motor up than run the MPG test. But this 5 pound doesn't make a difference. In a large truck the difference between 90 psi and 120 only gains about 0.25- 0.5 on vehicles that get 6 or 7 MPG so its getting you about 5-10% better mpg to have 33% more air in the tire (tires are rated to up to 120 but only 90 is need to carry the weight)
This make a big difference when you drive 400 to 700 miles in one day. not so much when you drive that in a month. DO NOT EXCEED THE MAX PRESSURE RATING OF YOUR TIRE as you drive the tire heats up and this can cause the tire to explode when driven @ high speed or long distances. The max pressure recommended by the car manufacture is less important than the one by the tire maker. Higher strength tires can support higher pressure and will often require it to keep the proper shape.
About the warming up thing... Your coolant gets to temperature before the heat is fully saturated throughout the engine and transmission.
Your topics are relatable for me u got a new follower 💖 keep it up
Just bought a vauxhall mokka the suggested eco setting on the door sticker is 39 front 41 rear thought thats gonna be too high so I had set them to 36 as a compromise the ride was so bumpy on bumpy roads even at 36 it must be awful at 39 lowered them now to the lowest 32 psi setting its improved the ride a lot. Not gonna bother chasing fuel economy with the pressures the suspension is stiff and short wheelbase doesnt help. I may set them higher for long journeys but around town a lot the bumpy potholes and speedbumps are awful in this car dont buy one if your looking for comfort even got one with leather seats but they are only comfortable when parked when driving the suspension is bad on this car
Woah I was just wondering about this and see this video pop up, interesting findings as always!
Coincidence this video coming out. I had to top my front tyres up last Wednesday, i checked them and they were at 21psi when they should have been between 30 and 33. They looked a little down but i didn't expect that much.
Wind direction maybe only thing I can think of great video tho as always
Fantastic video and explanation! Super detailes and helpful. I have to agree wirh the findings. My Audi recommends lower tures pressure for comfort which I find the ride softer and comfortable. Regarding fuel economy in the comfort pressure, I am getting the the as on normal pressure with better ride quality. I guese it's all about experimenting.
At higher speeds drag is a much greater force then rolling resistance, people often seem to not know or ignore that fact.
If you also factor in the economy of different tyre types/brands, they add up. For instance the difference between a tyre that has a rating of E at fuel economy versus a tyre that has a C fuel economy rating would be ~0.2 l/100km. So add that to the economy of +0.3 bar and you get roughly around 0.3-0.4-0.5 l/100km. That is quite the improvement.
That's a good point.
@@ConquerDriving Heck, with a chip tune you might even drop another 10% off the fuel consumption. I drive a Golf Mk7 and i have an average of 5l/100km. If i get 10% off that would be around 4.5l/100km, add more efficient tyres and run them with a slightly higher pressure and i might drop my average fuel consumption to a 4.2-4.4. Marginal gains, but they sure do add up.
I always go to the most PSI i can get without compromising comfort.
Once it start getting harsher ride, i go back
HANG ON! the cars trip computer is working out mpg by using fuel used vs distance travelled. Its working distance travelled by rotation of the tire not GPS. Therefore the lower tire pressure is being helped by the tire circumstance being reduced as it is squashed. So the car thinks it's travelled further!
That's a good point but it is a tiny difference in diameter. I would like to measure it but I don't think I can measure the wheels with that level of accuracy.
Can you make a video about the car economy it run at same rpm in different gears.
I may do in the future, thank you for your suggestion.
instead of driving at same speed you should drive at same RPM. Lower pressure gives smaller diameter of the wheel and your speed will not match, what means you could be driving slower than you think. Slower drive means less consumption. One more thing, due to inertia to keep car moving requires low amount of energy, but empty tires will make most of the difference on stop and go kind of drive where you need a lot of energy to do drastic change in motion. But whole point of correct tire pressure is tire grip and wear.
Before watching this video, let me guess the answer: "it depends", "please follow manufacturer guidelines" and "check tire pressure regularly".
My pre-watch guess at the video contents: higher pressure will usually lead to less rolling resistance, which means less wasted power. Running on nearly flat tires will have high rolling resistance. However, overfilling your tires will cause to uneven wear and a loss of grip as well as potential blow-out issues; underfilling your tires can help a lot with grip but will cause abnormal wear can cause the tire wall to crack, as well as resulting in difficulty keeping the car stable through even slight corners. Also, any fuel savings you might hope to get for overfilling your tire are likely to be marginal at best.
Find out the correct pressure for your car/tire/wheel combination and use that. Pressure will fluctuate with temperature, so you need to keep checking pressure as ambient temperature changes.
I imagine that optimal tire pressure falls along a bell curve. So if you put your PSI at the optimal, then as you drive it will only go downhill and will require more frequent upkeep to stay optimal.
For the average (lazy) car owner, manufacturers may over state the recommended tire pressure so that over the period between upkeep the tire improves a bit and then decreases. Sort of doubling the time someone needs to wait before adding air to their tires.
There is a website that provides the correct tyre pressures. All you need to do is input the car registration number and it gives you the results. I recently bought a new Ford Kuga St-Line X and the website matched the psi that the car had when I purchased it. 32 at the front and 33 at the back.
I have seen a website like that, I'm not sure how accurate they are though.
Hello Richard! Thank you for always making these great and insightful videos that we can't get anywhere else! I know I speak for many of your subscribers when I say I really value your first principles approach to driving and the assumptions people have about cars and related topics.
I'm curious to hear your thoughts about the idea of warming up the engine before starting to drive? Is this really beneficial from a fuel economy (or engine health) perspective? And how does this hold for petrol vs diesel cars? Thanks a lot in advance!
Thank you for watching. Everyone has their own opinion about warming up the engine before driving. My advice is to let it run for 5 to 10 seconds and then get moving, letting it warm up at idle will only use more fuel. But drive gently until it's up to temperature to help protect the engine.
@@ConquerDriving well noted, many thanks Richard!
10:02 maybe the wheels spin fast enough to overcome the resistance of the road due to more optimal momentum at 60 mph as opposed to 40mph, where the momentum is lower , making the tires work harder for every spin.
Interestingly my VW Golf has the same air pressure recommendations for front and rear tyres.
Serious Question: Don't you teach a "Schulterblick", like a quick glance over your shoulder, before changing lanes or turning in the uk? Over here its check center mirror, side mirror, signal, do a look over your shoulder, move the steering wheel. if you miss the view over your shoulder once or twice in your driving test you can fail easily.
It depends on the situation.
I check tire pressure about weekly or when there are temperature changes of 10 degress C
Last week we had 22-25°C
Today more like 10-13°C
Had to pump another 0.2bar into the tyres
May the creator raise you up for your videos
Doesn't over inflating tyres have less grip and therefore a slight safety concern. A feet or two in braking distance may mean the difference between being involved in an accident or not.
I recommend following the manufacturer's recommendations for this reason. Even tyre wear is a good sign.
Maybe at higher tyre pressures the circumference of the tyre is larger, so you're actually traveling faster at "20"mph? And the the opposite for the lower pressure, So at "20"mph you're actually travelling slower? I suppose you could check the footage and see if there's a time differential between starting and finishing the test?
At higher speeds this circumference difference could the counteracted by centrifugal force?
Tire manufacturer says 35psi, my door panel says 28psi on my 79 Lincoln. I've compromised at 29psi to keep the ride quality high, which is the point of a luxury car. But I've always worried about how it affects economy and most importantly, tire wear.
tire pressure should be set firstly by tire manufacturer recommendations, not car manufacturer
secondly, should be adjusted to the weather you drive in
car manufacturer pressure recommendations are for the tires it leaves the factory on
There are two major factors which I would consider caused the lower fuel consumption of your car with lower tyre pressures - Fist is reduced windage due to the car being slightly lower to the ground which allows the better aerodynamics of under the car (ground effect) and lower effective frontal area. The other maybe less important factors may be the tyre characteristics themselves including tread and sidewall for those particular tyres.
Richard's car show soon. I won't miss it if was on screen.
I'm your subscriber from Russia. Good video and important information.
I am kind of surprised to see that at higher speeds and lower pressures, the gas mileage loss is so slim. In hindsight it makes kind of sense, as at 60 mph the tire should expierience enough centrifugal force that the rubber expands to a point where it almost matches the diameter it would have under recommended pressures (decreasing its formerly raised contact patch and rolling resistance to almost a normal level, negating the mileage losses)
If that is true, it would also explain the lower mileage at 40 mph where the tires are exposed to less than half the centrifugal force so they cant quite strech enough and the rolling resistance remains higher than under normal conditions.
[The 20 mph results are quite a mystery to me so take the following with a Brick of salt: The results might be due to an everslightly smaller wheel diameter causing misreadings in the cars speed. The sensor at the axle/wheel only reports the amount of wheel rotations to the car, while ignoring the actual diameter of the wheel (which is smaller now due to lower pressures) so one might as well be travelling at 18 or 19 mph instead of 20 mph making the engine work easier and therefore burn that little bit less fuel.]
The confusing thing is that at 20mph there is very little wind resistance. 40mph might be more affected by tyre pressures than 60mph because at 60mph the rolling resistance plays a smaller factor in economy than the wind resistance.
It is possible that the lower pressure does in fact have lower rolling resistance. Lots of variable here. Isn't the point of the scientific method to confront our preconceptions with data? Just because you don't know why something isn't happening it doesn't mean that it isn't happening. Perhaps more accurate measurement equipment would give absolute confidence in the results.
In the bicycle world experiments have found that on rougher surfaces lower tire pressure reduce rolling resistance because there is less vibration transmitted to vehicle and vibration is basically vertical motion, which is an acceleration of the vehicle is a non-forward direction. It takes energy to accelerate that mass up and down (vibration).
Overinflated, wear on the inside; underinflated, wear on the outside, that I understand. But I've seen tire wears on alternate columns, like after a drive, the tire surface becomes striped, like dark-light-dark-light-dark. I wonder what caused that.
If someone has TMPS in their car, can you tell how much tyre pressure rise is monitored during city and highway drives and also mention the outside temperature.
Tyres lose about 1 PSI in the winter every month maybe 1.5 or 2 depending how cold it is. I always put my 69 plate Corolla to 38 PSI on all 4 when it was recommended at 36 and I get real good mpg on the road. Regularly at 45 to 70 mpg
The Corolla Hybrid gets exceptional fuel economy. Assuming you have the hybrid as they did sell a small petrol in the GB when the latest Corolla was released.
@@ConquerDriving I have the 1.2t and I get excellent economy. It has 9,900 miles on the odometer
electric scooter or bike riders know the results 36psi only got around mile before down 90 then 50psi got mile and half
fantastic video
Sometimes tyre pressure can also alter wheel alignment, causing more tyre scrub with higher pressure. I can feel the steering get a bit hard if I increase or reduce the pressure a lot.
Would be interesting to see the results on an alignment machine with the various tyre pressures.
Suspension geometry has nothing to do with tyre pressures! Tyre pressure relates to how much air is in a tyre, not how a wheel is aligned. Two different things.
Price of fuel has sky-rocketed now....Our Rav4 Hybrid is achieving well over 61 mpg (imp) on a trgular basis. We run our tyres at 38 psi. With fuel being over $2 a litre every cent counts.
We areaactually well under the tyre manufacturers max pressures......The vehicle manufacturers pressure recommendations for tyre pressure seems to be about comfort and less noise
That is impressive economy.
Does changing the tyre pressure alter the reading of the speedo relative to the actual speed of the car?
That's a good point, it would change a tiny bit. Lower pressures would mean you aren't going slower than recorded and higher pressures would be faster than recorded. The wheels will be spinning at the same speed but the wind resistance will be a tiny bit different. I doubt the difference will be noticed because I would guess it's less than 1mph difference.
@@ConquerDriving Effective rolling distance of the tyres changes with pressure. At lower pressures the effective rolling distance of each tyre per rev is reduced. This is how cars can tell if one tyre is reducing in pressure, it rotates more than the other tyres. So without checking the recorded milage of each of your runs you are not getting the true mpg as the car will think it has gone further with low pressures and a shorter distance at higher pressures. The effect of this is that if with lower tyre pressures you reduce your recorded mpg by 1% you may be going an actual distance of 101% of recorded distance and the two balance out. The mpg calculation in the car's computer is assuming the tyres are at normal running pressure and have the normal running distance per revolution.
I remember, years ago, watching a video where they had a camera set up to look at the tyres while driving. The higher the speed, the less the tyres were actually in contact with the road. I guess that could explain the 60mph figures.
Would you rather cycle with soft tyres or firm tyres? There is a good reason road/racing bikes have thinner tyres than mountain bikes.