It makes sense that the internal rim width in relation to the tire casing width is such an important factor. It determines the overall internal volume.
Very useful video presentation. Used it and I need to lower slightly my pressures. Old school mentality of higher is best now in this age needs to change. Thanks for providing it free online.
Sir, BIG Thank You for your Calculator. It is an Amazing Tool. My road bike and my wife's touring bike now roll as on pillows!! Simply Amazing. Usually been riding at 90 Psi, yet when tuned at 72.5 Psi according to your calculator........it's as riding on butter honey! Thank you, thank you, thank you. Smart work. ~ Rinoni Thank you. Th
This was a VERY interesting video. In watching it and then reading your responses to earlier comments I am surprised by two things. First, that you found no difference in regards to proper air pressure to run for tubular, tubeless, and clincher. I had assumed (incorrectly I now see) that tubular you should run at higher pressures, tubeless at lower, and clincher somewhere in between. My second surprise is that suppleness of the casing isn't a factor in what pressure to use. Again my assumption was the higher tpi (more supple) a tire the higher the pressure required to get the proper drop (thinking Berto 15%rule of days gone by). Those were my "surprise" findings, now to my question. I have a total system weight of 175 lbs. I have two wheelsets one tubular and one tubeless. I run Vittoria Corsa Speed tires on both. I run a 23mm up front (it measures 23mm tubular, but measures 25mm tubeless), and a 25mm rear (again in tubular form it measures 25, but in tubeless version it measures 27mm). The max and minimum pressures listed on the sidewall of the tubular by Vittoria is 115psi minimum and 200psi max. On their tubeless version it lists a minimum of 87psi and a max of 130psi. On your pro calculator it recommends for my tubuless tires a 91psi front (measured 25mm) and 83 rear (measured 27mm). This puts the rear BELOW Vittoria's recommended minimum of 87 psi. On my tubular tires it recommends a 104 psi front (measured 23mm) and 93.5 psi rear (measured 25mm). This is substantially BELOW Vittoria's recommended minimum of 115 psi. To muddy the waters even further, Vittoria itself has a tire pressure calculator (www.vittoria.com/us/tirepressure) and their recommendation is for 120psi front and 125psi rear on both the tubeless and tubular 320tpi Vittoria Corsa Speed tires at my system weight and mixed road conditions. Now to be honest, I would never run my tubeless at those high pressures for fear of blowing them off the rim. But I certainly would consider running the tubular at those pressures. So why the huge difference between your calculator and Vittoria's recommendation? What do you suggest I do?
Hi Josh, I'm loving the new world of safely running lower and appropriate pressures on my road and e-mtb bikes. I'm wondering if and when the calculator might move to accommodate fat-bike tire widths up to say 5" on a 4" wide rim so say 130mm widths? Even my rear 4.5" tire on a 95mm rim is 117mm wide and makes the calculator next to useless for this set-up. Cheers, and thanks for all the great work and media. David.
Great episode! I love the calculator and cannot wait to go out and do pressure testing rides on my TT-bike to optimize for my tarmac quality. What I would wish for is a possibility to take a screenshot with my phone and get inputs (width, surface quality, weight) on the same picture as the pressure. If that is durable I would also love a "testing" sheet, where I can test a course with different pressures and upload the files and see the rolling resistance. Like an integrated Chung-method.
Thanks Allan, love all of these ideas, some of them are out of the scope of our small team, but the testing sheets are something we are looking at now.. I have a version we use for our ProTour teams, so we will tweak that and offer it! You are correct, having an anchor sheet of paper from testing makes running the Chung in Aerolab so much easier and cleaner! Thanks again - Josh
I’ve become an evangelist for this calculator. I tell many people to stop complaining about road conditions and get your pressure right. I went from 110-105 to 90-86. This need for precision caused me to upgrade my 40 year old Silca. Hey my son needed a pump. Old faithful is still going.
Hello! Are the calculator recommendations for heavy riders (I am 90kg) based on actual data points you have on record from riders in this weight range, or are they just extrapolated from data from lighter riders?
Josh, great point on the front/rear weight distribution, especially when being particularly aggressive. No question my pinch flats (mentioned elsewhere in the thread) were proof of running "too close to the sun". Cannot go personally go below 100 psi if running 25 mm at the front. Running 90 psi at the rear seems to be working out nicely on a 28 mm tire.
Our calculator has a pinch flat estimator/warning, I'd be interested to hear if your setting trip that warning? You are also totally correct that the strictly weight distribution based calculators tend to leave you much more pinch flat prone on the front wheel.. since pinch flatting is based on impact energy it is actually more velocity sensitive even than weight.. so keep that in mind when using our calculator as well!
@@SILCAVelo Just had the chance to check out the pressure calculator at the Silca site. This was using the basic version, and it produced estimated values of 92 F, 95 R. The pinch flats occurred at 95 front, but there are a couple of caveats to consider. This most recent instance was definitely "operator error" as I rolled over a square cross-sectional steel tube that was difficult to pick up visually, as there was an overpass, where the natural light went from sun to shade to sun in the blink of an eye. The other incident took place on a paved pathway, where there are all kinds of dips and anomalies, but nothing that was super-obvious. You mentioned velocity - I was probably running 18-19 mph at the time of the incidents. I've still learned a great deal since I began riding the road bike 3 years ago. Early on, I would run sidewall max, and wonder why my fillings felt like they were coming loose! I'm a stronger and faster rider now, and the Silca blog has given me tons of food for thought as I continue to learn. Who knows - maybe my pump gauge is not accurate, and should be checked as well!
After 4 pinch flats in 5 rides I wised up and had 23mm tires replaced with 25mm. Had been using 125psi f+r but just not enough volume between road and rim. At 275lbs system all it took was a 3/4" chunk of gravel. Blam! Have found that even at 90 psi the 25mm tires seldom have a problem. With an aluminum track bike on the road 90 psi is a worthwhile tradeoff for me- pinch flat/ smooth ride/rolling resistance/tread puncture resistance. For me aero is not quite everything. It sure looked fast with those 23mms and 14 spokes up front but everything is a tradeoff. More aero without front caliper also!
David. Yes, 23mm tire is pretty small for that system weight! I'd imagine your 23's measured in the ~25-26mm range on wide HED rims, and your 25's are probably more like 28-29mm measured width on those rims. I get 80-90psi for your weight and those tires depending on surface.. so sounds like you've found a nice balance! If you're frame will hold something larger, I'd recommend it.. some 28mm G+ or GP5000 will measure 30-31mm on your wheels and be really perfect for that system weight.
@@SILCAVelo Yes but this is a $460 aluminum track bike! HED rims? The company states that 25mm is max for this frame. Curiously it came with 25mm tires that measure 26mm inflated 21mm outside rim width. Not afraid to experiment I took 14 spokes out of the 28 spoke front wheel! Now this actually did soften up the front slightly. No doubt this changed the spring rate. This performed well but always carried 2 spokes in my seatpost. I chickened out and put them all back In planning to do more long solo rides!
I only weigh 156 lbs., and have had two pinch flats on the front in recent months, running 95 psi in a 25 mm tire! I've had the bike for 3 years, and have experimented with both 25 and 28 widths. The 28 has a super-tight clearance in the fork, although part of that may have to do with Continentals just running on the large size. Currently going with a 25 front (at 100 psi) and 28 rear (90 psi), and I actually seem to be a bit faster than I am with 25 at both wheels. Still trying to determine that inflection point where aerodynamics and rolling resistance/impedance cross!
I run a 23 mm tire in the front and 25 in the rear (which blow up to 25 mm and 28 mm at pressure) on my TT / Tri bike. It would be great to have a drop down for different tire widths for the front / back of the bike!
Yes, you can just run it for the 23mm width tires and take the front value and then re-run it for the 25mm tire and use that as the rear value. Just be sure to use the actual measured widths of both.
Kind of confused by your updated calculator with regards to tire type. What would I select if I'm using high performance clinchers and butyl tubes? What about with latex tubes? Thanks!
How come there isn't a specific surface condition category for mountain biking? From the images, it would seem that one would select Category 4 Gravel. Just seems odd that some selectable fields have MTB-specific input, but Surface Condition doesn't spell it out.
If we're rolling for money, then I understand your reasoning about meters and seconds, but if I'm going to ride and rejoice, then I worry more about not getting a snake bite, because I'll be changing my rubber for an hour:-),"as simple as that. I have been pumping 100 on both wheels for 3 years and forgot about what it means to fix rubber.
Love your products, videos, and podcasts. My wife and I ride a tandem with total system weight approaching 325 lbs. We are working on a sub 5 hour century. My question is about weight distribution. Downhill, in the drops, is clearly the most important consideration. Is their a way to determine our weight distribution given individual rider weights? Can we correct from a static weight measurement? Thanks again for the fantastic content.
Could you add a two tire size field for the front and rear tires. The same width only in road bikes. In gravel and MTB, all use a wider front. In TT use a narrow front. It will be easier to put both sizes and do 1 calculation, but not do it twice and pick up numbers. Thanks!
Not sure if this has been asked already but, is there any plan to allow the tire width measurement to include decimal places? Or, is this difference so minimal that it doesn't even matter? Eg my front tire measures at 37.44 while the rear measures at 37.6 (35mm tires on 21 inch internal rim).
I ran the numbers using your calculator. Here are my results. I am 130lbs + 20lbs (150lbs) for bike, 2 filled bottles, food, pump, small multitool, extra tubes, clipless shoes, helmet, phone, etc. I ride a road bike with 28mm Specialized Turbo Cotton on HED Belgium+ which means they measure at 29mm~ or so. I have personally been running 49/50psi up front and 58-60psi rear. Now, the only reason I do so is because I feel this is the most comfortable and squishy ride I can get without risking pinch flats but yet your calculator gave me a different suggestion of 70psi front and 72psi rear? Would you mind elaborating on this? Should I change my pressure to the suggested tire pressure recommended by your calculator, or maybe even meet in between at the average for both front and rear tires respectively?
I'd say it's likely that the pressure the calculator is recommending is a bit faster than what you are on now providing the surface roughness you've chosen matches our model (this is the hardest part of the calculator to program and to use, so we continue to refine!). However, if you are happy with what you've got, you are probably in pretty good shape.. sounds like you aren't trying to squeeze those last couple of watts out of the bike and are more focused on comfort, so a bit lower is probably just right. I would recommend looking at your front rear bias.. if it's flat where you are it's probably no big deal, but differentials that high can cause sketchy handling on steep descents from my experience. - josh
SILCA Velo so you recommend running the front tire at a higher pressure (closer to what is recommended for the rear) for overall riding on flats, and climbing/descending?
@@astrayagrarian Yes, I never recommend front pressures lower than 93-95% of the optimal rear pressure as a rider with good road position will see roughly 48-52 up to 50-50 weight distribution when riding in the drops. Then on a steep downhill, the weight distribution moves even further forward placing higher loads on the front tire which can lead to squirm, vague handling, and if you are running low enough, can lead to casing damage of the tire. We measure many ProTour pros to have as much as 60% forward weight long Tour type descents and even higher in some of the crazy descending positions.
Curious, you were consulted on VeloNews Paris-Roubaix tires article where they used an air shock + rough surface to simulate the vibration losses that would be lost in rider’s body by way of heat. Interesting that they confirmed the U-shaped rr + ‘impedance’ curve the work you & Tom Anholt observed. One surprising thing not pointed out in article, but seems significant was that optimal pressure did NOT seem to be correlated to tire width.. also not correlated to tire rr 😳 Meaning that the assumption that a tire is just an air spring and an any differences in tire construction were negligible at best seems to be wrong! It seems like every tire model & width on a given surface has its own curve and so predicting with a tire pressure calculator (that assumes correlation of optimal pressure with tire width) is UNFORTUNATELY not possible? The construction of the tire seems to matter.. Comments?
Tubular vs tubeless vs clincher? Since it's pro data I would assume its from tubular tires. Wouldn't the rim cavity air volume of a tubeless make for a lower pressure?
Great Question and NO.. the type of tire and volume of air does not matter within the bounds of what is measurable in the real world. In the lab you can see something like the additional air volume in a tubeless tire vs tubular making
Hi Josh I got a question. How about for the bike touring or bikepacking guys? My friend and I use our bags differently. He puts them on his front rack, I hang them on my rear rack. When we add those weights and user preferences it might affect the calculations, am I wrong on that? Thanks a lot.
You can account for that in the weight distribution tab, and if that won't go far enough, then figure out your front/rear loads and use the calculator at 2x the rear load and 50/50 distribution to get the rear pressure, and then 2x the front load and 50/50 distribution to get the front pressure.
I realize this is an old thread but I'll ask my question anyway. I assume data is from people riding down the road smoothly pedaling in the saddle. This would be drastically different to sprinting. What adjustment to tire pressure needs to be done if the focus is winning a field Sprint type situation. The bike is moving side to side and the rider bouncing up and down. Any information out there?
Josh, thanks for sharing so much research. As a tiny person at 108 lbs, I have a different calculation than many riders. Are there any special considerations or advantages in tires/ tubes I should make? I now ride on 650b carbon 23 internal mm rim, extra light butyl inner tubes and extra light babyshoe pass 42mm tires at 20-39 lbs of pressure on worn pavement and cat 3 gravel. I've had one flat this year. I have not felt any low pressure issue on my 5-7 mile decent on worn pavement. I can still aggressively corner at 25 lbs of pressure with no tire call squirming/instability. I do begin to feel that my bike descends slower as my pressure gets closer to 20lbs. I appreciate any thoughts--if you have any.
I just ran your scenario in our calculator using 45-46mm measured width for that tire on a 23mm inner rim and assuming a 128lb system weight I'm getting 25psi for Cat3 Gravel up to mid 30psi for smoother surfaces.. Being very light affords you all sorts of advantage with tires and pressures, so you have more room to experiment than us heavier guys! The one change I would make is to either latex inner tubes, or running tubeless.. even very light butyl tubes will cost you a couple watts per wheel and for very small and light riders frictional losses make up a larger percentage of loss as you are naturally a bit more aero!
For pure hillclimbing you can calculate this and then enter those numbers into the calculator for weight, but we do not recommending making changes like this for mountain riding as they will then leave you way overpressure in the rear when descending leading to reduced rear traction and increased likelihood of rear brake lockup when descending.
Typical day riding starts with my bike coming from my cool basement out to 75 degree farenheit weather. Let a few psi out through valve, and put 85psi into front tire, 90 rear. Weight of rider= 235lbs. + 18lbs aluminum track bike. 25mm Continental Gatorskins, 19mm inside bead width rims. Lowest psi I can get away with. Conditions fair chipseal to smooth fine asphalt. Is it my imagination or did that setup work better in winter, and 3 hours in 85 degree heat became way too much psi. Feel I'm really getting beat up later in ride. Effect of darkness in asphalt a factor?
Yes, 3 things at play here.. tire PSI will increase ~1psi for every 10 degree Fahrenheit increase in temperature.. so just sitting there, 85psi pumped into the tire at 50deg first thing in the morning will be 88psi sitting there if the temp goes to 80 deg later in the day. Second, the tire is warmed additionally by the road surface which is primarily heated by sun.. so first thing in the AM when it is dark, the road surface is generally very close to the ambient temperature, but by mid-day the road surface will be 20-30 deg higher than the ambient (this is HUGE in auto racing where temperature is heavily related to grip). Lastly, your Gatorskins are incredibly high hysteresis and therefore rolling resistance tires. They are quite flat proof, but along with being very slow, they will heat due to deformation and remain warmer than other tires. Of the 3 effects, this one is by far the smallest in terms of pressure increase, but also remember that high hysteresis tires can have much higher dynamic stiffness behavior than supple tires at the same PSI, so the negative effects here begin to compound as things get warm! - Josh
@@SILCAVelo Could using latex tubes be a strategy for late ride "Iron Wheel Syndrome"? Portable pressure gauge, or too risky with no pump to correct a mistake? Yes, Gatorskins I always suspected were high histeresis tires. Briefly considered Tanus tires because I was getting so many flats. The OEM Kenda Kriterium tires that came with the bike were prone to punctures and casing damage. I remember riding Campionato del Mondo silks decades ago and they were smooth!! You can have fast, light, or cheap, pick 2 ! Locked into 25mm tires. Maybe Continental 5000 for front only. Probably wouldn't go back to 14 front spokes to soften things up. Not feeling lucky!
On a 50 mile group ride here in South Florida, our Surface Conditions will vary greatly from Worn Pavement, New Pavement and some Concrete sections. How do you factor that in? Also, it's very difficult to read and set the tire pressure with my analog SILCA floor pump with a large dial. What Digital Presta Pressure Gauge would you recommend to get accurate tire pressure readings?
PS: Forgot to mention I use a size 23 Front Tire that measures 26.5mm and 25 Rear Tire that measures 27mm. I can only select 26mm or 27mm in the calculator. I cannot enter an exact measurement. To calculate the pressure I selected 26mm for the front and 27mm for the rear.
Yes, just set the surface condition to track. At least 100 data points in the algorithm come from track testing including some short/steep ones, both wood and concrete. System weight is rider plus equipment.. so if you were to step on a scale wearing your full kit holding your bike.
My dilemma is that (perhaps incorrectly so) for my TT (Long Course Tri) I've been running 23mm tyres on the front and 25mm on the rears. The calculator doesn't compensate for the changes in tyre width ( or do I run it for 23mm to get the front pressure recommendation then re-do it for the rear? Especially as I'm assuming a 50/50 weight distribution?)
Yes, you can just run it for the 23mm width tires and take the front value and then re-run it for the 25mm tire and use that as the rear value. Just be sure to use the actual measured widths of both.. this is probably the most important aspect of the whole calculator!
Deformable surfaces are the holy grail of modeling right now and quite honestly, nobody can do it at scale yet.. in motor racing tire manufacturers are using crazy CFD/FEA combinations to model the surfaces as a fluid to try and solve this! In general, once you have a deformable surface like mud or sand, which is essentially 100% hysteresis loss.. you want to deform it as little as possible, so tire pressure should be as low as is safe against pinch flatting or wheel damage. In a couple UCI world cups last year, I had riders using 17-19psi in their 32-33mm approved tires on muddy surfaces with great results. Nothing in the current calculator will get you that low, but you can start with the harshest surface option as a starting point and then reduce from there.
Recreational assumes 14-18mph average speed. This is used in calculating the probability of having an impact that could cause a pinch flat, so if the calculator finds that at your weight you would have to hit a pothole edge at 28mph to pinch flat, the percentage of time you are going 28mph as a recreational rider is less than 1%, whereas it might be more like 25% of the time if you were riding pro speeds.
You mention pro files... is the data in pro files some how inherently more valid than any other data? I'm wondering because the pressures recommended are quite a bit higher (~25-30psi) than another calculator that also takes into account impedance (67kg, 27mm,700c). Does your algorithm biasing your recommended pressures based on pressures pros use? Given that pros tend to be very conservative, slow to change traditions etc I would think they would be hard to convince to use lower pressures, tubules etc. Wish list... - clincher, tubular, tubeless tire options.. - ability to enter % of each surface type so you can pick a pressure that is best overall
I compared if me and bike were 87km (191lbs) vs 67kg (147lbs).. so 44lb difference! and that results in a 3psi difference in terms of optimal pressure..? ..that, just anecdotally seems wrong..?
We are the only calculator that I am aware of that uses calculated impedance values.. so what you have here is the result of thousands of actual field test calculations to find peak minimal rolling resistance, and we then fit an algorithm to that to help interpolate the empty spaces.. so for example, we have more than 120 optimizations across 5 teams, 30 athletes and 4 tire sizes all done in the Carrefour de l'arbre.. so we then curve fit for 26mm tires, riders 165-210lbs system weight.. then we fit for 28mm tire data, then for 30mm tire data and so on. Each of these tests originally having the result of being the actual pressure used by that athlete on that day. Our data comprise more than 20 pro triathletes across 4 years ad 5 tire widths on the Queen K at Ironman and so on.. from that, we've built the algorithm to predict the likely peak minimum rolling resistance likely for your weight, tire size and surface. All other calculators that I know of use either % drop of tire on a flat surface for a given load OR height of drop on a flat surface for a given load. Both of these methods are good starting points to begin the optimization process, but are only indicative of static tire stiffness on a flat surface and have nothing to do with impedance or any of these other factors that prove out to be critical in the real world. Also important to note that most calculators by manufacturers are also constraining their data by the max pressure of the rim or tire being sold.. so many of them will take %drop and then just shift the results or limit the results based on these stated pressure limits. I love your idea on % of surface per ride, we use this in our pro team optimizations and do plan to include it at some point in a future version of this calculator. As for tire type, this has proven not to affect pressure in real world testing. Since the pressure is controlling the spring rate and the tire construction is controlling the hysteresis this makes sense, think of tire pressure as being the spring in your suspension and the tire construction as being the damper.. across small changes in damping, the optimal spring rate remains unchanged.
This is because our minds tend to approach all problems as being linear.. so a 25% change in system mass should result in ~25% change in pressure. However, the tire stiffness and spring rate behavior is non-linear to tire size and is also non-linear to bump input performance...and also remember that the calculator is trying to find the optimal middle ground between impedance which is non linear AND casing losses which are also non-linear. This is definitely an area where the mathematical model has not caught up to the field testing work that has been done, so we aren't yet in the best spot to have tested a hypothesis detailing the specifics, but I can tell you that nothing about any of it is linear. This could also be a place where having the entirety of the data set based on pro athletes could skew the data.. they are all much lower body fat and higher muscle % than the rest of us which theoretically lowers impedance which would also theoretically increase the impedance pressure break point.. but again, this is the data set that we have.
So this FastFitnessTips calculator is combining % drop and mm of drop data and does not have any functionality to predict impedance. This is the type of calculator that we used years ago to find a starting point to begin optimization and our calculator is based on the results of all those optimizations.
I like the Silca pressure guide, however I always find myself on the very low side of things (20-21 psi based on wide gravel tyres), this is lower than the manufacturer's minimum psi. Is this common?
It is still rather common to find optimal pressure below the range on the sidewall. Much of this is due to the antiquated pressure systems that manufacturers are using.. this is changing, just not very quickly. If you aren't having pinch flats at the recommended pressures you will be fine.
I think your calculator is OVERLY optymistic ... for example, MTB 29x2.4 tires (62mm), worst surface (gravel cat 4), 90kg system weight and the calc proposes 0.8 bar !!! it's not possible to take a turn with such pressure. 1.4-1.6 bar is realistic... and what about road tires? 29mm, high perf, good pavement - 5.3-5.4 bar (I think you've updated the calc, before it was lower?) - This works, however I have a question, why tire manufactures suggest higher pressure? even minimum more like 6 bar (continental and pirelli for example)
As alternative i would recommend the sram calculator with more options like tyre type, different tyre dim and more if needed: axs.sram.com/guides/tire/pressure
It makes sense that the internal rim width in relation to the tire casing width is such an important factor. It determines the overall internal volume.
Very useful video presentation. Used it and I need to lower slightly my pressures. Old school mentality of higher is best now in this age needs to change. Thanks for providing it free online.
Sir, BIG Thank You for your Calculator. It is an Amazing Tool. My road bike and my wife's touring bike now roll as on pillows!! Simply Amazing.
Usually been riding at 90 Psi, yet when tuned at 72.5 Psi according to your calculator........it's as riding on butter honey!
Thank you, thank you, thank you.
Smart work.
~ Rinoni
Thank you. Th
So glad to hear! Best!
Im no expert but i think Josh deserves a Nobel
Watched the whole video.. now to go to the calculator and see how it does in the real world. Will leave my email.. thanks!
This was a VERY interesting video. In watching it and then reading your responses to earlier comments I am surprised by two things. First, that you found no difference in regards to proper air pressure to run for tubular, tubeless, and clincher. I had assumed (incorrectly I now see) that tubular you should run at higher pressures, tubeless at lower, and clincher somewhere in between. My second surprise is that suppleness of the casing isn't a factor in what pressure to use. Again my assumption was the higher tpi (more supple) a tire the higher the pressure required to get the proper drop (thinking Berto 15%rule of days gone by). Those were my "surprise" findings, now to my question. I have a total system weight of 175 lbs. I have two wheelsets one tubular and one tubeless. I run Vittoria Corsa Speed tires on both. I run a 23mm up front (it measures 23mm tubular, but measures 25mm tubeless), and a 25mm rear (again in tubular form it measures 25, but in tubeless version it measures 27mm). The max and minimum pressures listed on the sidewall of the tubular by Vittoria is 115psi minimum and 200psi max. On their tubeless version it lists a minimum of 87psi and a max of 130psi. On your pro calculator it recommends for my tubuless tires a 91psi front (measured 25mm) and 83 rear (measured 27mm). This puts the rear BELOW Vittoria's recommended minimum of 87 psi. On my tubular tires it recommends a 104 psi front (measured 23mm) and 93.5 psi rear (measured 25mm). This is substantially BELOW Vittoria's recommended minimum of 115 psi. To muddy the waters even further, Vittoria itself has a tire pressure calculator (www.vittoria.com/us/tirepressure) and their recommendation is for 120psi front and 125psi rear on both the tubeless and tubular 320tpi Vittoria Corsa Speed tires at my system weight and mixed road conditions. Now to be honest, I would never run my tubeless at those high pressures for fear of blowing them off the rim. But I certainly would consider running the tubular at those pressures. So why the huge difference between your calculator and Vittoria's recommendation? What do you suggest I do?
Did you get and answer, i run similar system than yours and I really wonder about the tubular pressure
Hi Josh, I'm loving the new world of safely running lower and appropriate pressures on my road and e-mtb bikes. I'm wondering if and when the calculator might move to accommodate fat-bike tire widths up to say 5" on a 4" wide rim so say 130mm widths? Even my rear 4.5" tire on a 95mm rim is 117mm wide and makes the calculator next to useless for this set-up. Cheers, and thanks for all the great work and media. David.
Great episode! I love the calculator and cannot wait to go out and do pressure testing rides on my TT-bike to optimize for my tarmac quality. What I would wish for is a possibility to take a screenshot with my phone and get inputs (width, surface quality, weight) on the same picture as the pressure. If that is durable I would also love a "testing" sheet, where I can test a course with different pressures and upload the files and see the rolling resistance. Like an integrated Chung-method.
Thanks Allan, love all of these ideas, some of them are out of the scope of our small team, but the testing sheets are something we are looking at now.. I have a version we use for our ProTour teams, so we will tweak that and offer it! You are correct, having an anchor sheet of paper from testing makes running the Chung in Aerolab so much easier and cleaner! Thanks again - Josh
I’ve become an evangelist for this calculator. I tell many people to stop complaining about road conditions and get your pressure right. I went from 110-105 to 90-86. This need for precision caused me to upgrade my 40 year old Silca. Hey my son needed a pump. Old faithful is still going.
Hello! Are the calculator recommendations for heavy riders (I am 90kg) based on actual data points you have on record from riders in this weight range, or are they just extrapolated from data from lighter riders?
Thanks for this , It does seem to produce figures a lot lower than others.
Josh, great point on the front/rear weight distribution, especially when being particularly aggressive. No question my pinch flats (mentioned elsewhere in the thread) were proof of running "too close to the sun". Cannot go personally go below 100 psi if running 25 mm at the front. Running 90 psi at the rear seems to be working out nicely on a 28 mm tire.
Our calculator has a pinch flat estimator/warning, I'd be interested to hear if your setting trip that warning? You are also totally correct that the strictly weight distribution based calculators tend to leave you much more pinch flat prone on the front wheel.. since pinch flatting is based on impact energy it is actually more velocity sensitive even than weight.. so keep that in mind when using our calculator as well!
@@SILCAVelo Just had the chance to check out the pressure calculator at the Silca site. This was using the basic version, and it produced estimated values of 92 F, 95 R. The pinch flats occurred at 95 front, but there are a couple of caveats to consider. This most recent instance was definitely "operator error" as I rolled over a square cross-sectional steel tube that was difficult to pick up visually, as there was an overpass, where the natural light went from sun to shade to sun in the blink of an eye. The other incident took place on a paved pathway, where there are all kinds of dips and anomalies, but nothing that was super-obvious. You mentioned velocity - I was probably running 18-19 mph at the time of the incidents. I've still learned a great deal since I began riding the road bike 3 years ago. Early on, I would run sidewall max, and wonder why my fillings felt like they were coming loose! I'm a stronger and faster rider now, and the Silca blog has given me tons of food for thought as I continue to learn. Who knows - maybe my pump gauge is not accurate, and should be checked as well!
After 4 pinch flats in 5 rides I wised up and had 23mm tires replaced with 25mm. Had been using 125psi f+r but just not enough volume between road and rim. At 275lbs system all it took was a 3/4" chunk of gravel. Blam! Have found that even at 90 psi the 25mm tires seldom have a problem. With an aluminum track bike on the road 90 psi is a worthwhile tradeoff for me- pinch flat/ smooth ride/rolling resistance/tread puncture resistance. For me aero is not quite everything. It sure looked fast with those 23mms and 14 spokes up front but everything is a tradeoff. More aero without front caliper also!
David. Yes, 23mm tire is pretty small for that system weight! I'd imagine your 23's measured in the ~25-26mm range on wide HED rims, and your 25's are probably more like 28-29mm measured width on those rims. I get 80-90psi for your weight and those tires depending on surface.. so sounds like you've found a nice balance! If you're frame will hold something larger, I'd recommend it.. some 28mm G+ or GP5000 will measure 30-31mm on your wheels and be really perfect for that system weight.
@@SILCAVelo Yes but this is a $460 aluminum track bike! HED rims? The company states that 25mm is max for this frame. Curiously it came with 25mm tires that measure 26mm inflated 21mm outside rim width. Not afraid to experiment I took 14 spokes out of the 28 spoke front wheel! Now this actually did soften up the front slightly. No doubt this changed the spring rate. This performed well but always carried 2 spokes in my seatpost. I chickened out and put them all back In planning to do more long solo rides!
I only weigh 156 lbs., and have had two pinch flats on the front in recent months, running 95 psi in a 25 mm tire! I've had the bike for 3 years, and have experimented with both 25 and 28 widths. The 28 has a super-tight clearance in the fork, although part of that may have to do with Continentals just running on the large size. Currently going with a 25 front (at 100 psi) and 28 rear (90 psi), and I actually seem to be a bit faster than I am with 25 at both wheels. Still trying to determine that inflection point where aerodynamics and rolling resistance/impedance cross!
The sticker is awesome. I'll check out the calculater too :-)
Thanks!
I run a 23 mm tire in the front and 25 in the rear (which blow up to 25 mm and 28 mm at pressure) on my TT / Tri bike. It would be great to have a drop down for different tire widths for the front / back of the bike!
Yes, you can just run it for the 23mm width tires and take the front value and then re-run it for the 25mm tire and use that as the rear value. Just be sure to use the actual measured widths of both.
Kind of confused by your updated calculator with regards to tire type. What would I select if I'm using high performance clinchers and butyl tubes? What about with latex tubes? Thanks!
How come there isn't a specific surface condition category for mountain biking? From the images, it would seem that one would select Category 4 Gravel. Just seems odd that some selectable fields have MTB-specific input, but Surface Condition doesn't spell it out.
If we're rolling for money, then I understand your reasoning about meters and seconds, but if I'm going to ride and rejoice, then I worry more about not getting a snake bite, because I'll be changing my rubber for an hour:-),"as simple as that. I have been pumping 100 on both wheels for 3 years and forgot about what it means to fix rubber.
Love your products, videos, and podcasts.
My wife and I ride a tandem with total system weight approaching 325 lbs. We are working on a sub 5 hour century. My question is about weight distribution. Downhill, in the drops, is clearly the most important consideration. Is their a way to determine our weight distribution given individual rider weights? Can we correct from a static weight measurement?
Thanks again for the fantastic content.
Could you add a two tire size field for the front and rear tires. The same width only in road bikes. In gravel and MTB, all use a wider front. In TT use a narrow front. It will be easier to put both sizes and do 1 calculation, but not do it twice and pick up numbers.
Thanks!
Not sure if this has been asked already but, is there any plan to allow the tire width measurement to include decimal places? Or, is this difference so minimal that it doesn't even matter? Eg my front tire measures at 37.44 while the rear measures at 37.6 (35mm tires on 21 inch internal rim).
I ran the numbers using your calculator.
Here are my results. I am 130lbs + 20lbs (150lbs) for bike, 2 filled bottles, food, pump, small multitool, extra tubes, clipless shoes, helmet, phone, etc.
I ride a road bike with 28mm Specialized Turbo Cotton on HED Belgium+ which means they measure at 29mm~ or so.
I have personally been running 49/50psi up front and 58-60psi rear. Now, the only reason I do so is because I feel this is the most comfortable and squishy ride I can get without risking pinch flats but yet your calculator gave me a different suggestion of 70psi front and 72psi rear?
Would you mind elaborating on this? Should I change my pressure to the suggested tire pressure recommended by your calculator, or maybe even meet in between at the average for both front and rear tires respectively?
I'd say it's likely that the pressure the calculator is recommending is a bit faster than what you are on now providing the surface roughness you've chosen matches our model (this is the hardest part of the calculator to program and to use, so we continue to refine!). However, if you are happy with what you've got, you are probably in pretty good shape.. sounds like you aren't trying to squeeze those last couple of watts out of the bike and are more focused on comfort, so a bit lower is probably just right. I would recommend looking at your front rear bias.. if it's flat where you are it's probably no big deal, but differentials that high can cause sketchy handling on steep descents from my experience. - josh
SILCA Velo so you recommend running the front tire at a higher pressure (closer to what is recommended for the rear) for overall riding on flats, and climbing/descending?
@@astrayagrarian Yes, I never recommend front pressures lower than 93-95% of the optimal rear pressure as a rider with good road position will see roughly 48-52 up to 50-50 weight distribution when riding in the drops. Then on a steep downhill, the weight distribution moves even further forward placing higher loads on the front tire which can lead to squirm, vague handling, and if you are running low enough, can lead to casing damage of the tire. We measure many ProTour pros to have as much as 60% forward weight long Tour type descents and even higher in some of the crazy descending positions.
Uso muito essa calculadora para gravel.
Curious, you were consulted on VeloNews Paris-Roubaix tires article where they used an air shock + rough surface to simulate the vibration losses that would be lost in rider’s body by way of heat. Interesting that they confirmed the U-shaped rr + ‘impedance’ curve the work you & Tom Anholt observed.
One surprising thing not pointed out in article, but seems significant was that optimal pressure did NOT seem to be correlated to tire width.. also not correlated to tire rr 😳
Meaning that the assumption that a tire is just an air spring and an any differences in tire construction were negligible at best seems to be wrong!
It seems like every tire model & width on a given surface has its own curve and so predicting with a tire pressure calculator (that assumes correlation of optimal pressure with tire width) is UNFORTUNATELY not possible? The construction of the tire seems to matter..
Comments?
Tubular vs tubeless vs clincher? Since it's pro data I would assume its from tubular tires. Wouldn't the rim cavity air volume of a tubeless make for a lower pressure?
Great Question and NO.. the type of tire and volume of air does not matter within the bounds of what is measurable in the real world. In the lab you can see something like the additional air volume in a tubeless tire vs tubular making
Hi Josh I got a question. How about for the bike touring or bikepacking guys? My friend and I use our bags differently. He puts them on his front rack, I hang them on my rear rack. When we add those weights and user preferences it might affect the calculations, am I wrong on that?
Thanks a lot.
You can account for that in the weight distribution tab, and if that won't go far enough, then figure out your front/rear loads and use the calculator at 2x the rear load and 50/50 distribution to get the rear pressure, and then 2x the front load and 50/50 distribution to get the front pressure.
I realize this is an old thread but I'll ask my question anyway.
I assume data is from people riding down the road smoothly pedaling in the saddle. This would be drastically different to sprinting.
What adjustment to tire pressure needs to be done if the focus is winning a field Sprint type situation. The bike is moving side to side and the rider bouncing up and down.
Any information out there?
How does Josh's hair constantly see a 100mph wind?
Can you calculate tire pressure for a recumbent trike?
Josh, thanks for sharing so much research. As a tiny person at 108 lbs, I have a different calculation than many riders. Are there any special considerations or advantages in tires/ tubes I should make? I now ride on 650b carbon 23 internal mm rim, extra light butyl inner tubes and extra light babyshoe pass 42mm tires at 20-39 lbs of pressure on worn pavement and cat 3 gravel. I've had one flat this year. I have not felt any low pressure issue on my 5-7 mile decent on worn pavement. I can still aggressively corner at 25 lbs of pressure with no tire call squirming/instability. I do begin to feel that my bike descends slower as my pressure gets closer to 20lbs. I appreciate any thoughts--if you have any.
I just ran your scenario in our calculator using 45-46mm measured width for that tire on a 23mm inner rim and assuming a 128lb system weight I'm getting 25psi for Cat3 Gravel up to mid 30psi for smoother surfaces.. Being very light affords you all sorts of advantage with tires and pressures, so you have more room to experiment than us heavier guys! The one change I would make is to either latex inner tubes, or running tubeless.. even very light butyl tubes will cost you a couple watts per wheel and for very small and light riders frictional losses make up a larger percentage of loss as you are naturally a bit more aero!
Hi Josh ! Do u think and advice different pressure balance for road bike but like on mountain stages ?
Because of the load that is heavier on the Rear wheel on climbs 🤷♂️
For pure hillclimbing you can calculate this and then enter those numbers into the calculator for weight, but we do not recommending making changes like this for mountain riding as they will then leave you way overpressure in the rear when descending leading to reduced rear traction and increased likelihood of rear brake lockup when descending.
Nice video Josh, what do you think of the fastfitnesstips calculators on tire pressure? especially the one where you input the surface type
I haven't used it, but will take a look at it, thanks.
Hi Josh, regarding tire quality, how would you rate Schwalbe Thunder Burt Super-race setup tubeless?
Typical day riding starts with my bike coming from my cool basement out to 75 degree farenheit weather. Let a few psi out through valve, and put 85psi into front tire, 90 rear. Weight of rider= 235lbs. + 18lbs aluminum track bike. 25mm Continental Gatorskins, 19mm inside bead width rims. Lowest psi I can get away with. Conditions fair chipseal to smooth fine asphalt. Is it my imagination or did that setup work better in winter, and 3 hours in 85 degree heat became way too much psi. Feel I'm really getting beat up later in ride. Effect of darkness in asphalt a factor?
Yes, 3 things at play here.. tire PSI will increase ~1psi for every 10 degree Fahrenheit increase in temperature.. so just sitting there, 85psi pumped into the tire at 50deg first thing in the morning will be 88psi sitting there if the temp goes to 80 deg later in the day. Second, the tire is warmed additionally by the road surface which is primarily heated by sun.. so first thing in the AM when it is dark, the road surface is generally very close to the ambient temperature, but by mid-day the road surface will be 20-30 deg higher than the ambient (this is HUGE in auto racing where temperature is heavily related to grip). Lastly, your Gatorskins are incredibly high hysteresis and therefore rolling resistance tires. They are quite flat proof, but along with being very slow, they will heat due to deformation and remain warmer than other tires. Of the 3 effects, this one is by far the smallest in terms of pressure increase, but also remember that high hysteresis tires can have much higher dynamic stiffness behavior than supple tires at the same PSI, so the negative effects here begin to compound as things get warm! - Josh
@@SILCAVelo Could using latex tubes be a strategy for late ride "Iron Wheel Syndrome"? Portable pressure gauge, or too risky with no pump to correct a mistake? Yes, Gatorskins I always suspected were high histeresis tires. Briefly considered Tanus tires because I was getting so many flats. The OEM Kenda Kriterium tires that came with the bike were prone to punctures and casing damage. I remember riding Campionato del Mondo silks decades ago and they were smooth!! You can have fast, light, or cheap, pick 2 ! Locked into 25mm tires. Maybe Continental 5000 for front only. Probably wouldn't go back to 14 front spokes to soften things up. Not feeling lucky!
On a 50 mile group ride here in South Florida, our Surface Conditions will vary greatly from Worn Pavement, New Pavement and some Concrete sections. How do you factor that in? Also, it's very difficult to read and set the tire pressure with my analog SILCA floor pump with a large dial. What Digital Presta Pressure Gauge would you recommend to get accurate tire pressure readings?
PS: Forgot to mention I use a size 23 Front Tire that measures 26.5mm and 25 Rear Tire that measures 27mm. I can only select 26mm or 27mm in the calculator. I cannot enter an exact measurement. To calculate the pressure I selected 26mm for the front and 27mm for the rear.
Is your calculator suitable for track riders? 90 kilo sprinter +9 kg bike going flying 200m on a high banking Velodrome means 200 kg system weight?
Yes, just set the surface condition to track. At least 100 data points in the algorithm come from track testing including some short/steep ones, both wood and concrete. System weight is rider plus equipment.. so if you were to step on a scale wearing your full kit holding your bike.
My dilemma is that (perhaps incorrectly so) for my TT (Long Course Tri) I've been running 23mm tyres on the front and 25mm on the rears. The calculator doesn't compensate for the changes in tyre width ( or do I run it for 23mm to get the front pressure recommendation then re-do it for the rear? Especially as I'm assuming a 50/50 weight distribution?)
Yes, you can just run it for the 23mm width tires and take the front value and then re-run it for the 25mm tire and use that as the rear value. Just be sure to use the actual measured widths of both.. this is probably the most important aspect of the whole calculator!
What surface category would you suggest for winter cyclocross (i.e. very soft mud)? That's the only racing where I really think about pressure a lot
Deformable surfaces are the holy grail of modeling right now and quite honestly, nobody can do it at scale yet.. in motor racing tire manufacturers are using crazy CFD/FEA combinations to model the surfaces as a fluid to try and solve this! In general, once you have a deformable surface like mud or sand, which is essentially 100% hysteresis loss.. you want to deform it as little as possible, so tire pressure should be as low as is safe against pinch flatting or wheel damage. In a couple UCI world cups last year, I had riders using 17-19psi in their 32-33mm approved tires on muddy surfaces with great results. Nothing in the current calculator will get you that low, but you can start with the harshest surface option as a starting point and then reduce from there.
@@SILCAVelo Makes sense, it's definitely like riding through porridge. Thanks!
Can you explain what speeds are included into recreational cycling?
Recreational assumes 14-18mph average speed. This is used in calculating the probability of having an impact that could cause a pinch flat, so if the calculator finds that at your weight you would have to hit a pothole edge at 28mph to pinch flat, the percentage of time you are going 28mph as a recreational rider is less than 1%, whereas it might be more like 25% of the time if you were riding pro speeds.
You mention pro files... is the data in pro files some how inherently more valid than any other data? I'm wondering because the pressures recommended are quite a bit higher (~25-30psi) than another calculator that also takes into account impedance (67kg, 27mm,700c). Does your algorithm biasing your recommended pressures based on pressures pros use? Given that pros tend to be very conservative, slow to change traditions etc I would think they would be hard to convince to use lower pressures, tubules etc.
Wish list...
- clincher, tubular, tubeless tire options..
- ability to enter % of each surface type so you can pick a pressure that is best overall
I compared if me and bike were 87km (191lbs) vs 67kg (147lbs).. so 44lb difference! and that results in a 3psi difference in terms of optimal pressure..? ..that, just anecdotally seems wrong..?
FastFitnessTips Calculator here...
docs.google.com/spreadsheets/d/10878Rq_wnurkcdIyhklZ0Y6ARx6xxdLMZ_9Xj9hgmZ4/edit#gid=1388801070
We are the only calculator that I am aware of that uses calculated impedance values.. so what you have here is the result of thousands of actual field test calculations to find peak minimal rolling resistance, and we then fit an algorithm to that to help interpolate the empty spaces.. so for example, we have more than 120 optimizations across 5 teams, 30 athletes and 4 tire sizes all done in the Carrefour de l'arbre.. so we then curve fit for 26mm tires, riders 165-210lbs system weight.. then we fit for 28mm tire data, then for 30mm tire data and so on. Each of these tests originally having the result of being the actual pressure used by that athlete on that day. Our data comprise more than 20 pro triathletes across 4 years ad 5 tire widths on the Queen K at Ironman and so on.. from that, we've built the algorithm to predict the likely peak minimum rolling resistance likely for your weight, tire size and surface. All other calculators that I know of use either % drop of tire on a flat surface for a given load OR height of drop on a flat surface for a given load. Both of these methods are good starting points to begin the optimization process, but are only indicative of static tire stiffness on a flat surface and have nothing to do with impedance or any of these other factors that prove out to be critical in the real world. Also important to note that most calculators by manufacturers are also constraining their data by the max pressure of the rim or tire being sold.. so many of them will take %drop and then just shift the results or limit the results based on these stated pressure limits.
I love your idea on % of surface per ride, we use this in our pro team optimizations and do plan to include it at some point in a future version of this calculator.
As for tire type, this has proven not to affect pressure in real world testing. Since the pressure is controlling the spring rate and the tire construction is controlling the hysteresis this makes sense, think of tire pressure as being the spring in your suspension and the tire construction as being the damper.. across small changes in damping, the optimal spring rate remains unchanged.
This is because our minds tend to approach all problems as being linear.. so a 25% change in system mass should result in ~25% change in pressure. However, the tire stiffness and spring rate behavior is non-linear to tire size and is also non-linear to bump input performance...and also remember that the calculator is trying to find the optimal middle ground between impedance which is non linear AND casing losses which are also non-linear. This is definitely an area where the mathematical model has not caught up to the field testing work that has been done, so we aren't yet in the best spot to have tested a hypothesis detailing the specifics, but I can tell you that nothing about any of it is linear. This could also be a place where having the entirety of the data set based on pro athletes could skew the data.. they are all much lower body fat and higher muscle % than the rest of us which theoretically lowers impedance which would also theoretically increase the impedance pressure break point.. but again, this is the data set that we have.
So this FastFitnessTips calculator is combining % drop and mm of drop data and does not have any functionality to predict impedance. This is the type of calculator that we used years ago to find a starting point to begin optimization and our calculator is based on the results of all those optimizations.
On good pavement, never under 8.5bar for me.
I like the Silca pressure guide, however I always find myself on the very low side of things (20-21 psi based on wide gravel tyres), this is lower than the manufacturer's minimum psi. Is this common?
It is still rather common to find optimal pressure below the range on the sidewall. Much of this is due to the antiquated pressure systems that manufacturers are using.. this is changing, just not very quickly. If you aren't having pinch flats at the recommended pressures you will be fine.
@@SILCAVelo Thank you. Just need that extra confidence.
I think your calculator is OVERLY optymistic ... for example, MTB 29x2.4 tires (62mm), worst surface (gravel cat 4), 90kg system weight and the calc proposes 0.8 bar !!! it's not possible to take a turn with such pressure. 1.4-1.6 bar is realistic...
and what about road tires? 29mm, high perf, good pavement - 5.3-5.4 bar (I think you've updated the calc, before it was lower?) - This works, however I have a question, why tire manufactures suggest higher pressure? even minimum more like 6 bar (continental and pirelli for example)
As alternative i would recommend the sram calculator with more options like tyre type, different tyre dim and more if needed: axs.sram.com/guides/tire/pressure
This suggested a psi nearly 3 times higher for myself .