Do Wider Tyres RUIN Brake Performance?
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- čas přidán 7. 07. 2024
- And does a 'slip ratio' actually measure how much your tyres is slipping or skidding along the road under braking etc, or something else?
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In this module, just one of many taken from the HPA Brake System Design and Optimization course, you will explore the fundamental mechanisms behind how tires generate longitudinal force. The amount of longitudinal force a tire can generate while braking depends on various parameters, with the slip ratio being the primary influencer. Vertical load, slip angle, camber angle, temperature, inflation pressure, and vehicle speed also play important roles.
For every set of conditions, there exists an optimal slip ratio that maximizes the generation of longitudinal force, also referred to as braking force. The slip ratio experienced by the tires is primarily determined by the driver's application of brake pedal force.
Furthermore, we will discover how the coefficient of friction produced by the tires during braking is sensitive to the vertical load.
Don't worry! All the basics like 'what even is vertical load and longitudinal force' are also covered before getting stuck into things!
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TIME STAMPS:
0:00 - Complexity & Parameters
1:17 - Slip Ratio Visualisation
1:55 - Under Braking Vs Free Wheeling
2:04 - Example
2:13 - Important Clarification
2:37 - Force Vs Slip Ratio
3:20 - Linear, Transitional and Friction Ranges
4:07 - You Don't Want This
4:58 - Vertical Load
6:03 - Implications & Tyre Width
6:59 - Rubber/Compound
7:26 - Wider Vs Inflation Pressure
8:02 - Non-linear
8:16 - Road Racing
8:40 - Tyre Data
8:50 - Key Points
9:37 - BUILD | TUNE | DRIVE
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TAGS:
#highperformanceacademy #brakes #tires #tyres #braing #calipers #brakesystem #brakerepair #buildtunedrive #learndriveoptimise #motorsport #auto #carmods #automotive - Auta a dopravní prostředky
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Tire width in relation to diameter primarily effects the contact patch shape, and how that contact patch deforms and changes under load. This will effect handling charactersitcs of a car but not really "increase grip". Two differently shaped tires at the same pressure will have the same amount of grip, it will just be distributed in a different way.
Race cars use wide tires because it distributes the car's weight more evenly putting less stress on the sidewall and carcass, which allows them to run lower tire pressures, which increases the contact patch size and thus the total grip. If you look online at some tire's specs you can see the load rating of each tire, which is basically the how strong the tire is and gives you an idea of how low of a pressure you can run for a particular weight of car without compromising it's structural integrity. If you look online you can see that some narrower tires have a higher load rating then wider ones of the same make and compound, which means you can actually run a lower pressure on the narrower tires and have more grip than the wide ones.
It seems to me that many use too big and wide tyres. Especially on the street.
Having the right tyre for the car could possibly give better acceleration, more responsive handling and better braking. And that tyre might just be smaller than youd think. Especially on a lighter car.
Since tyre size and width is alot about looks its not surprising people are confused.
Its even more the case with brakes. (Remember size isnt in the equation..)
everyone talking about weight but no mention of downforce - a car might be light, too light for the width of tyre - but what about a light car with 500-1000kg of downforce - what size tyre then?
Excellent content as usual 👍, also depending on the type of suspension a wider tyre along with track alters the leverage load to the spring / shock . Also the heavier mass due to a wider tyre / rim alters the frequency of the suspension due to un sprung weight. Always check your shocker/ dampers after the upgrade as the may well go out of range in either wet or dry conditions. A we’ll set up and valved damper should ideally be set half way on the adjustment allowing clicks either way allowing softer settings for wet and harder settings for dry. This then also effects the anti roll bar settings. All very involved but interesting and also sometimes depends on one’s driving style too . Some drivers trail brake and then apply the break to first scrub speed off and others use heavy breaking to transfer weight to the front axle , this then gives more grip on turn in but only momentarily.
Hope this helps anyone.
SUBSCRIBED! These are the kinds of things i think about, but i rarely meet anyone who understands or even cares. Love it, this whole channel.
Great vid, I went with a narrower tyre last time, it's only for street use where I thought you may be able to keep slightly more heat in a narrower tyre, also allowed a square setup rather than staggered, seems to have worked out alright, looks like onto the flat patch vid now lol
More distribution of weight over the tyre surface will result in negative braking performance in the wet. So many 4wd/suv owners don't understand that their huge tyres tend to aquaplane on wet roads. The flintstones car would have had fantastic grip in the dry with those 2 huge front & back rollers but a pain in the arse in the wet.
This same logic applies to race slick tires as well. Of course they won't perform well on a wet surface because they have no tread but more than makes up for maximum grip on dry tarmac.
You may be mis-understanding what "aqua-planing" actually is? Certainly, there appears to be a typo', at best?
@@gordowg1wg145 No, that is aquaplaning in a nutshell. Nobody will run slicks in the rain because people know that normal slick tires have zero traction on a wet track surface, unless you have specialized rain tires. The inly thing that traditional slick tires are goid for is racing on dry tarmac and nothing else.
@@TheSilverShadow17
Nope - while you are correct in that "slick" tyres are often severly compromised on "wet" surfaces, when aqua-planing occurs the tyre is physically lifted from the surface. There are other factors, such as the porosity of the track surface and/or rubber laid down, and a very important part is the temperature of the tyre surface.
Provided there isn't actual standing water - the track surface being merely wet - and and the driver still able to keep heat in the tyres, there may not be that much time lost, especially as intermediate and, especially, full wets can overheat if there isn't enough water on the track.
Even narrow tyres, with full tread depth, can suffer from true aqua-planing - I've even had it at quite low speeds, 60-70 mph, while driving on the road, with front wheel drive vehicles, where water has pooled in depressions. The engine rpm and speedo' rising and falling as the tyre(s) would lose and gain traction.
@@gordowg1wg145 Even the slightest disturbances in the behavior of vehicles can throw them off quite drastically on most occasions, because when the tires make contact with a puddle of water they're not only dealing with surface composition changes but temperature changes as well in that same instant. You've helped reinforce the topic with your response but I'm typically referring to heavy rainfall on a road surface where tons of water has built up over time that hasn't yet evaporated or absorbed by the asphalt/tarmac.
How do you addapt a tire in a light car sub 1000kg for proper braking without the presure being so low you give up lateral grip?
I didn't understand Connor's explanation of how a larger contact patch affects available traction. He seems to imply "we can't know the result." I thought the answer was clearly "a larger contact patch means less load per area therefore higher coefficient of friction."
Hi guys, thanks for the good content. I have a question. If I mount tires with 10% more grip, does it make more sense to increase the spring rate by 10% or to increase the spring rate so that the spring frequency is 10% higher? ( It's just a theory)
so if I'm understanding this right
a wider set of the same tire compound can potentially create a larger contact patch than before in the front under braking
which will distribute the loading, thus potentially having less friction coefficient loss in the front under heavy braking, which when compared to the rear coefficient, has the slight possibility to change oversteer dynamics under braking? ie, rather unintuitively, could be more understeery depending on compound/pressure/suspension? which seems intuitive actually, big tire grip more, if front more slip angle vs rear = more understeer
A softer compound will deform under stress whether that be acceleration which causes the tyre to flex outwards & shape like a doughnut & decreases contact with the surface (watch top fuel drags) or under braking where the tyre squishes into the surface & increases contact area due to the transfer of weight on braking
As i always say: tires and air flow - these are the only 2 things that the car interacts/communicates with the outside world.
I dont understand the part about vertical load vs coeff of friction. My understanding was that the coeff of friction (u) is a constant, based on mechanical properties between the two surfaces. I can understand how u could change over time eg with differences in tyre temperature, but changes due to the vertical load do not make sense to me, as the vertical load is N in the friction equation, F=uN, which implies u and N are independent?
I am going to guess it has to do with tread deformation, but I don't really know. The simple F = uN formula does not take into account the dynamic effect of what happens to the tire as it experiences different loads.
Tires are deceptively complicated. As I understand it molecular adhesion and tread surface compliance to small imperfections in the surface of the road (Milliken calls this "gearing", but I've also seen it called "indentation") are what generate grip between the road surface and the tread of the tire. It's not like there is one mu value for a tire in all conditions. I think far more complex modeling is required to understand the actual forces between the road surface and the tire tread.
In most cases you'd be correct where COF stays relatively consistent with vertical load, but rubber is a special case. @Fix_It_Again_Tony is on the right track with "tread deformation" and viscoelastic nature of the rubber. Very simply put more load makes it more difficult for the rubber to deform which is involved in molecular adhesion and therefore grip.
Tires are complex, but this is the reason why load transfer reduces total grip - Connor
@@hpa101 ah ok that makes sense, thanks!
Imagine in the extreme case of a piece of tape attached to a desk. Since the force resisting motion in a piece of tape derives from adhesive forces rather than interaction from normal forces, the resisting force is independent of the normal force and therefore doesn’t have a meaningful coefficient of friction
Will we have a shorter braking distance if the wheel rotates slightly slower than the vehicle speed would indicate (in a light slip), or if we keep the wheel speed the same as the speed of the slowing vehicle?
My empirical "street experience" (im not a racing driver and, never any measurements taken) tells me, that a car brakes better and accelerates better if the wheels are kept in a slight slip.
Generally having a little bit of slip (5-10% if I remember correctly, I'd reccomend you check since I mightve forgotten the proper value) is ideal for braking
You need the correct size tyre for the vehicle weight/load and it’s ability to build heat into the rubber.
Too much surface area and the load is spread over a large surface area and doesn’t build heat( friction ), too small and it will overheat from to much friction.
That is all else being equal, tread block design, rubber chemical composition and tyre pressure.
Wider tires increase braking performance when same type and pressures are used in the dry, period.
Anyone who says different is selling you a lie.
Everything else equal Wider tires don't necessarily mean more contact patch area. It's probably a wider contact patch, but will also likely be shorter in the longitudinal direction, which is more important to braking.
But if the contact patch is increased, this will lower the surface pressure between the tire and road surface, increasing the coefficient of friction leading to more grip.
Wider tires can and generally do increase grip, no one is arguing that, but it's a bit more complicated and whats most important in any case is controlling the contact patch - Connor
It doesnt have to be complicated though when the end result can be summed up. If someone is not pairing their wheels and tires to the width they are running, that's a whole other different issue. Every record is done with wider tires. scca nationals is nothing but 275+ squared setups and they dont even go over 70mph most times or the biggest they can run, gunma record is held by a 300ish hp car running 295/30s. I understand on paper everything you're saying is great, but in the real world, more width is just better, if the car isnt properly setup for that width, that is a build/setup issue, not a tire too wide issue. Their is a reason exotics dont come with 245 or 265s for "better braking and handling" its gullible at best to assume any car when setup properly will be better off with a less width tire unless rules restrict the tire size and you are forced. On paper you can make anything make sense to a degree, fortunately this hardly ever transfers to the real world... EA the "super conductor" that failed after stating "they figured out the math" @@hpa101 Show me ONE top 10 placing time attack car under a 275 that's not limited by class or awd. weight of a normal car isnt a f1, wider the better.
Guys, why knock monitor video has gone? Upload again, plzzzzz
That was a members lesson. We stream them live then they end up in the members lesson archive for 12 months or more before they are uploaded here for good (that gives members a chance to get value from their membership first). You can find it on the website here: www.hpacademy.com/previous-webinars/340-plex-knock-monitor-v3/
The transcript and time stamps will be added in the next 7 days as well.
Hope that helps! - Taz.