Finding the perfect tire pressure

There’s a lot of talk about optimizing tire pressure these days. In years past, most of us inflated our tires to the maximum pressure rating shown on the tire sidewall. It’s more complex now. Like Goldilocks, we add air and then let out some again, until we’ve found what seems to work best. And then we still wonder whether we’re giving up speed and/or comfort. Would we be faster if we increased the pressure to optimize our tires for the smoother parts of the ride? Or should we let out air for the rougher sections?

The truth is quite liberating: Tire pressure matters less than most people think. We’ve tested this dozens of times – most recently in our latest tire tests that we’ll publish soon: On smooth pavement, higher tire pressure doesn’t make your bike significantly faster. On the left, you see the performance of our Cayuse Pass Standard 700C x 26 mm on smooth pavement. Whether we inflated them to 75 psi or 95 psi made no difference in their performance. It took 209 Watts to pedal the test bike at 19.3 mph (31 km/h), no matter the pressure.

What does make a difference is choosing tires with a supple casing. The third tire in the comparison required 11% more power to roll at the same speed. That’s huge.

The graph on the right shows the power required to ride on really a rough surface – in our case, rumble strips, but the same applies to cobblestones or rough gravel. In that case, the lower pressure was faster. A lot faster – 18% to be exact. Saving 82 Watts just by letting out some air is , especially as this also makes the bike more comfortable. Even so, we needed to put out almost twice as much power to keep the speed the same as on the smooth pavement. Wider tires and lower pressures would have narrowed that gap.

In summary, lower pressure doesn’t slow you down on smooth asphalt, and it makes you faster on rough surfaces. So it makes sense to err on the low side when choosing your tire pressure for mixed-surface rides. Of course, you don’t want to go too low, either.

If your pressure is too low, the tire can collapse during hard cornering. What happens is that the tire deforms too much. The more the tire flexes, the easier it is to deform it… The result: Your tire just folds over.

The good news is that with supple tires, you rely less on the stiffness of the tire casing to hold up the bike, so removing that part of the equation has less serious consequences. Tire collapse is less abrupt than it is with stiff sidewalls, where, one moment, your tire is holding up the bike fine, and then, without much warning, it suddenly folds over. During the early days of riding wide tires, the BQ team saw a number of collapsing tires, but they’ve never caused a crash. Having a tire collapse can be very scary – and it certainly slows you down!

The photo above shows my front tire almost collapsing during very hard cornering. It didn’t collapse, and I never noticed anything strange until I looked at the photo…

Now I have to admit that I was cornering pretty hard, enjoying the amazing grip you get on warm pavement. My inside pannier was dragging on the ground… My front wheel carried the load for a two-day trip, and I was trail-braking to maximize front-wheel traction as I banked the bike into the sharp downhill turn. Earlier, I had let out air for the rough portion of the old road across Jikkoku Pass in Japan. With my 42 mm tires, 28 psi or thereabouts (1.9 bar) is great for riding on rough trails, but it’s not quite enough for spirited descending on pavement.

Usually, when your tire is about to collapse, you notice that your bike is running wide in sharp corners. The wider your tires, the more noticeable this is. When I run my Firefly with its 54 mm tires on rough gravel, I often decrease the tire pressure to about 20 psi. If I then tackle a paved descent without airing up the tires again, the bike doesn’t like to turn into hairpins, giving me ample warning that my pressure is too low.

There is another issue with supple, wide tires: Lower pressures make the tire follow cambers in the road more. Rather than climb out of a rut in the pavement, the tire will just flex. (Sorry, I have no photo of that, so here’s one that shows how much a supple tire with a large sidewall can flex.) Air up a little more, and your bike feels more like a performance bike. On the road, I run my Firefly’s 54 mm tires at 32-35 psi, and it feels like a racing bike that is almost unaffected by these cambers.

There’s also the longevity aspect of your tires. If you run your tire pressure very low, it’ll put more stress on the casing. If you’re running tubes, that’s usually not a problem. Tubeless, the casing can start to leak. You’ll see dirt collect on the tire sidewalls where the sealant is evaporating as it leaks through the sidewall. Usually it takes a few thousand miles before this happens, so if you can accept that your tire wears out before the tread is too thin to ride safely, then this isn’t a problem. (You can always continue to run your tire with tubes when you get to this stage.) Or air up your tires a bit more, and you’ll reduce the wear on the tire casing.

So in summary, don’t worry about performance when airing up your tires. Instead, think about the handling, feel and safety you want and need. You don’t want your tires to collapse during hard cornering, but above that threshold, there is a large plateau where your tires will perform fine. Experiment with tire pressure and see what feels good to you.

31 Responses to Finding the perfect tire pressure

  1. Alexandru T July 28, 2020 at 6:06 am #

    Hi Jan! Thank you for the very interesting article.

    I find this series of posts demystifying tires and the things around them truly great!
    Spent already too much time wondering what pressure to run or if i should run 700c or 650b and so on… without any means of objectively clarifying the differences.

    I do see a reference to your Standard casing in the article as example of a supple tire.
    One thing that i don’t understand yet (even after reading your Casing article) is how Standard and Endurance casings compare against each other.

    I think it’s an important aspect as for example myself am looking for something a bit more resilient compared to the Extralights. My Barlow Pass Extralights where quite nice (despite the more challenging tubeless experience) but for the kind of rides i do – long leisure rides into unknown terrain – i appreciate a tire that is a bit more resilient, as long as comfort is not compromised. I never sliced a tire sidewall, but i do run over glass or road debris from time to time, and the last thing i’d like to worry about on my rides is fixing a flat.
    So in my case i am faced with choosing between Standard and Endurance casing, without clear comparison between them head to head.

    How i understand them so far agains each other:
    Standard
    + lower price
    + more supple?how much?

    Endurance
    + better puncture protection due to extra layer
    + potentially easier tubeless experience

    -> But how do they compare on comfort and speed?
    -> Would you say that if you are willing to spend the extra money that the Endurance is a better casing then the Standard? Or are they just different casings?
    -> How do they compare when using them with the Schwalbe extralight tubes?

    Would love to be able to try them side by side but i’m afraid that’s quite impractical. Had to pay quite a premium in Europe for a pair of Endurance Hurricane Ridge, can’t imagine getting also a pair of Standards just to do A/B testing 🙂

    Really appreciate more insight into this comparison.

    Cheers!

    • Jan Heine July 28, 2020 at 9:01 am #

      Those are good questions! We are working on getting some real numbers. We’ve done preliminary testing, but nothing that meets the scientific standards our readers expect from us. The simple fact is that tire testing under real-world conditions takes a lot of time and perfect conditions (no wind, constant temperatures) that don’t occur often. And to get a handle on the very small differences between the Standard and Endurance casings (the Extralight’s advantage is easier to measure!), we needed to come up with a different testing method. At road speeds, there is too much noise from small changes in rider position to get data that has the resolution we need. Which also shows you that the difference is small enough that you probably wouldn’t worry about it…

      More specifically to your question, the puncture resistance is the same between Standard and Extralight, since the tread is the same, and a supple casing doesn’t contribute much to puncture resistance. The Endurance has an additional cut-resistant layer, so it’s more puncture-resistant, but that also makes it a bit less supple. This is compensated to a large degree by the more supple casing compared to the Standard, so your choice makes sense.

      On the other hand, I run Extralights on almost all my adventures. Especially with tires wider than 40 mm, you’re unlikely to have trouble due to the low pressure at which you are running the tires. When I ran 21.5 mm supple tubulars, I had a flat every other race until I installed tire wipers. Now I don’t bother with tire wipers, yet I average one or two flats a year.

      • Toni July 28, 2020 at 10:40 am #

        The difference between extralight, standart and endurance would be very interesting to see. I bought the Rat Trap Pass Endurance and i am wondering if i should bought the extralight version or a narrower tire (less weight) to be faster, but then i would need sealant in my tubes. I am experimenting with tubeless and i didnt found that the endurance casing is leaking or sucking up the sealant in the casing, so i think it could be faster to run tubeless then with tubes, cause the casing isnt clogged and slowed down with sealant. Am i right? I work as a bike courier so i need some protection…

        • Jan Heine July 28, 2020 at 10:47 am #

          Narrower tires aren’t faster, so the Rat Trap is a good choice. The difference between running tubes and sealant is too small to worry about – many claim that tubeless is faster, but that hasn’t been confirmed in real-world testing. So yes, you’d be faster on the Extralight, but if a flat means getting in trouble with work, the Endurance gives you peace of mind.

  2. Andrew Stow July 28, 2020 at 6:59 am #

    I’m rolling on Switchback Hills, and have settled on 28 PSI front, 38 rear. I’m running tubeless and still have some slow leaks as I get it dialed in. I recently got home from work and thought my tires looked a bit low as I went over bumps, but it was riding fine including cornering well. I was at 15/27 PSI. Definitely a very tolerant system!

    Total weight bike + rider + gear is about 190-195 lb.

  3. marmotte27 July 28, 2020 at 7:21 am #

    I always find your tire pressures especially low. Ok, some of the difference may depend on the pressure gauge of my pump, but at the same time, I never get tire flex looking like yours, so I certainly run higher pressures than you.
    I get the uncomfortable tire-want’s to stay- in-the-rut flex at about 2.7front/3.2 rear bar in my standard casing LoupLoupPass, and at that pressure I’m always in fear of bottoming out on rough roads (I’m running my tires with tubes).
    So without luggage, I now run 3.2 front/3.5 rear, with a camping load I run 3.7front/3.9rear. No worries of bottoming out with that.

    • Jan Heine July 28, 2020 at 8:53 am #

      Tire pressure depends on so many factors. Most important is obviously the weight of rider/bike/luggage. The photo with the front panniers was during a ride where I didn’t really consider that weight. When I saw the photo after returning from our trip, I was surprised because the tire handled just fine. If the bike had run wide, I definitely would have noticed on that road!

  4. Pk July 28, 2020 at 11:11 am #

    Anecdotal story. Had a Honda V6 Accord that needed tires. The dealer had a very light, inexpensive 30K tire with super flexible light sidewalls. After 2 tanks of gas my mpg went from 22 to 26 and the car absolutely floated over bumps.

    • Jan Heine July 28, 2020 at 1:40 pm #

      Love that story, but the scientist in me says that the difference seems like a lot for a car tire. Could it be that the diameter was different and hence your odometer reading was off?

  5. Brian Roth July 28, 2020 at 12:03 pm #

    Please define ‘trail braking’. Not familiar with that term.

    • Jan Heine July 28, 2020 at 1:42 pm #

      When you brake, you transfer weight to the front wheel. When you enter a corner, you can use that effect to increase traction on the front wheel: Rather than finish all your braking before the corner, continue to brake into the corner. You’ll find that you have much more traction, and the bike (or car, if works there, too) turns in much more sharply. Of course, braking also puts higher demands on the traction, so you don’t want to use that technique when it’s slippery. And you want to release the brake as you lean the bike into the turn and approach the limit.

  6. Mark Mullen July 28, 2020 at 12:55 pm #

    I have religiously followed your advice on tire pressure over the years and it has served me well for randonneuring, touring, event rides and commuting The chart that you published some time ago concerning how to modify tire pressure relative to weight was particularly valuable.

    Where I’ve struggled to apply any of this, however, is for folding bikes, particularly my Bike Friday which I use for light loaded touring. For starters, tires with supple sidewalls just do not exist for 20 inch wheels! Many of these bikes use a variant of the venerable Schwalbe Marathon which “helpfully” recommends a tire pressure between 55 and 100 PSI. Surprisingly, the Friday touring community is often frustratingly vague on this issue, with tire pressures seeming to be a matter of “until it feels right;” a process that is more aggravating with a loaded bike than with a clean one.

    Do you have any data from your own tests or others dealing with non-standard tire sizes? The folding bike commuting community is already a large one, and folding touring is increasing with popularity due to airline price gouging. Given BQ’s welcome emphasis on practical cycling it would be nice to maybe throw a little love toward the folders.

    • Jan Heine July 28, 2020 at 1:44 pm #

      We haven’t tested small wheels. That said, there isn’t much reason why tire pressure should be radically different for small wheels. The contact patch is a bit shorter, so you may want to increase pressure a little, but it’s probably not enough to really make a difference. I think the advice “what feels right” is a good starting point!

    • John C.Wilson July 28, 2020 at 2:14 pm #

      Look into BMX tires. There are lots of high end tires marketed. Much new product I am not familiar with. The venerable and still available Panaracer HP406 has family resemblances to a Pasela and family resemblances to RH. Still made in Japan. Just installed a pair of those on an old Raleigh Twenty in use as the wife’s winter bike. Which is adjustable and easy for the larger member of the family to test ride. Made the bike get up and go.

    • Grant July 29, 2020 at 4:40 am #

      I have some experience with unloaded mini velos. If you’re riding wide 20s on rough surfaces, you sort of have no choice but to run high pressure because the smaller wheels strike the bump later and by the time the tire caves in, the axle is already on top of the bump. Have you ever heard of rimpact, cushcore, etc? Google it. The hype is real. If you can run tubeless this would be an excellent choice for you. Maybe email rimpact and ask about a product for a 20 inch wheel, they are a small company and will probably be responsive and help point you in the right direction. This way, you can run decently comfy pressure and not worry about rim strikes.

    • Paul Greenberg July 30, 2020 at 4:45 am #

      I have a BF Pocket Rocket with 451 20″ rims and use Schwabe One tires with decent results. I use the Berto chart and find the recommended pressure to be pretty close to perfect.

  7. Rick Thompson July 28, 2020 at 2:34 pm #

    Do you understand why sealant starts to leak from older EL sidewalls? I would expect that if a pore opens up the sealant would, well, seal it. It can seal tiny thorn holes and big gashes, why not a porous sidewall?

    • Jan Heine July 28, 2020 at 4:59 pm #

      What seems to happen is that the threads in the casing move too much for the sealant to work long-term. A small cut or hole will seal, as long as the surrounding material is stable. If the weave moves constantly, the sealant can’t seal it.

  8. Stuart Fogg July 28, 2020 at 5:41 pm #

    Before the Snoqualmie Pass tires became available I tried a pair of supple 48 mm tires from another company (also made by Panaracer). On 21 mm rims they felt unsteady in crosswinds and over ruts even at pressures between 40 and 45 psi. Barlow Pass tires felt fine on those same rims at every pressure I tried.

    When I got my Snoqualmie Pass (Endurance) tires I mounted them on 30 mm rims. I know that’s overkill but they feel great down to 35 psi. Since I use tubes I haven’t tried lower pressures. Of course rims that wide require disc brakes.

  9. Kai S July 29, 2020 at 2:08 am #

    as for extreme rim width i have tested the same 2,25 rocket ron/thunder burts mounted on standard 21i inner width crest rims, vs in parallell a second pair on 40i easton arc rims. cornering with low pressures certainly gets better with greater tolerance for low pressures, but a most definite and somewhat surpricing effect is a noticeably improved rollout with the (over)wide rims, both on rough and smooth surfaces.

    normally i use these 40i rims with 2.6 tyres making them work charmfully. roots and rocks are ignored, stability at speed is great, rollout is in par with the fastest. for 3.0 tyres these rims are too narrow; to get stability from burping and when cornering you very obviously have to pump them up to bouncyness, and useful pressure window is very narrow, or just not quite there.

    the test of 2.25s on the same 40i rims was just a test nevertheless going on for some months, and the sweet spot for 2.25s between weight, rollout and cornering stability at low pressures would be less wide. my uneducated guess is 30-35i. and at pressures desired for rough surfaces definitely nowhere near 21i. that width i now consider useful only for high speed/higher pressure use.

    i know you have been skeptical on the effects of rim width, Jan. but i am positive that you are in for a revelation here, once you in your usual scientific manner try it out:)

    • Stuart Fogg July 30, 2020 at 9:46 am #

      The people at FLO cycling mention wider rims (up to a point) give lower rolling resistance. However their published tests include only road tires from 25 to 32 mm on 17 and 21 mm rims. They also say their 25 mm gravel rim is optimized for a 37 mm tire with a range of 32 to 48 mm.

      Another benefit they claim for their rims is air resistance, not much of a factor at speeds I ride.

  10. Kai S July 29, 2020 at 2:15 am #

    as for folders i wrote in a previous column about the suppleness of older model brompton standard tyres. they are really quite supple and rollout when going in a club peleton by no means handicapped compared to the racers. i weigh 73 kg, use 3.5 – 4 bars roughly 60 psi, if i exceed that pressure rollout suffers as does puncture resistance. with lower pressure snakebite punctures when during commute climbing sidewalk curbs becomes a problem.

    the since long present alternative schwalbe marathon standard model has been popular on bromptons, but its really dreadfully slow and stiff. it may be improved by sanding away some of the too thick shoulder rubber, where i personally believe most of the damage of thick-walled tyres takes place. actually makes a difference.

    on brompton’s new standard tyre, the marathon racer this seems to have been taken into account, it has a noteably thinner shoulder tread as well as soft side carcass, and its actually a pleasantly light rolling alternative, able to cope also with rougher road surfaces and winter use.

    this tyre is produced in a number of other sizes.

  11. Grant July 29, 2020 at 4:25 am #

    Images like the one at the top of this post re-ignite my instinct that there is something to be said for slightly wider rims. My personal opinion is that they keep the contact patch underneath you better during hard cornering, at the expense of shock absorption/ ride quality/rolling resistance. Slow mo videos of F1 cars show the same behavior of the sidewall folding, but of course it’s not as scary on a four wheeled vehicle. The entire car oscillates a bit. Not a sensation I want on my bicycle!

    I am building a new wheelset around 48c tires and I’ll be using 30mm rims to mimic the same ratio as my old road bike (15mm rims, 23mm tires). I think narrower rims are still the right choice for knobby tires since the knobs do some flexing, thus reducing the maximum momentary force that would otherwise be completely handled by the sidewall. For the record, I am aware that I am thinking very hard about this 🙂

    • Jan Heine July 30, 2020 at 7:20 am #

      Rim width doesn’t make any perceptible difference with tire collapse. In fact, one reason I’ve found the ‘wider rims allow you to run lower pressure’ idea not to work even with stiff mountain bike tires is that once they start collapsing when you hit a bump in a corner, there is even less air pressure holding you up. When I rode a bike with WTB tires at Paul Camp a few years back, the mechanics told me that on rocky terrain, I needed at least 30 psi. That’s more than I’d ride with supple tires of that width on that terrain.

      • Stuart Fogg July 30, 2020 at 10:03 am #

        Thanks for the great (and scary) picture of tire collapse. Thankfully I’ve never experienced that but I do feel an everyday handling difference with wider rims. Perhaps that’s related to lateral stiffness. In the extreme case of zero rim width and perfectly flexible sidewalls the sidewalls would leave the rim horizontally and a small lateral displacement would produce no restoring force. That effect should be more pronounced with very wide tires at very low pressures.

        • Jan Heine July 30, 2020 at 12:00 pm #

          Your example of zero rim width, with the sidewalls leaving the rim horizontally, describes a tubular tire. And yet tubular tires corner very well – which is why most professional racers use them in mountainous races like the Tour de France. This also shows why rim width doesn’t make much difference with supple tires.

          • Stuart Fogg July 30, 2020 at 1:35 pm #

            The tubular rims I could find (Mavic Open Pro, HED C2, and Velocity Major Tom) have widths from 21 to 23 mm and are concave where they contact the tire. Mavic recommends 20 – 22 mm tires, HED recommends 23 – 32 mm tires, and Velocity recommends 25 – 35 mm tires. If the tire section is circular and contacts the rim at its edge then I think the angle (from horizontal) of the sidewall where it meets the rim would be arcsin(rim/tire). With any of the above recommended tire/rim combinations that would be significantly greater than zero.

            As long as the glued rim/tire connection is stronger than the frictional tire/road connection the tubular will never separate from the rim. You can corner as hard as your grip and skill allow. Can’t say that about clinchers.

  12. Kai S July 30, 2020 at 9:22 pm #

    tubular tyres also get support from a comparatively wide rim bead:)

    at higher should we say typically tarmac pressures rim width is not an issue when it comes to cornering
    stability.

    but same-same tyres still roll better on a wider rim. this effect may surprise some, but is definitely there, and also in accordance with the finding that wider tyres roll better.

    its in that respect just a different way of getting a wider contact patch, with less acute tyre deformation at its edges.

  13. Michael Banks July 30, 2020 at 10:30 pm #

    The Berto chart is a valuable tool. He did empirical measurements with a hydraulic jack and a caliper. Sounds crude, but he was careful and methodical in his approach. Another approach that does not include rider weight as a variable is to apply casing tension calculations where inflation pressure and tire diameter are the variables. It is counterintuitive to many people including bike geeks, and engineers that are not versed in this special field of mechanical engineering. The physical principal that underlies the relationship is called Laplace’s Law (http://hyperphysics.phy-astr.gsu.edu/hbase/ptens.html#lap). This helped me make some intuitive sense out of the relationship between tire width, inflation pressure and rider weight. If you assume tire wall thickness in constant, you can calculate an equivalent pressure, e.g. a 25mm tire at 75 psi will have the same casing tension as a 42mm tire at 52 psi. That will put you in the ball park anyway.

    • Jan Heine July 30, 2020 at 10:51 pm #

      Interesting! From a rider’s perspective, 25 mm tires at 75 psi is reasonable for my weight, but 52 psi for a 42 mm tire is far too much. This would indicate that the casing tension on the wider tire – which runs at something like 35 psi – is much lower. Perhaps that’s why you’re much less likely to cut a sidewall on a wider tire.

      • Stuart Fogg July 30, 2020 at 11:50 pm #

        Jan’s take makes sense to me. You only need enough pressure to avoid bottoming out and the section of a wider tire is not only wider but also deeper. Handling may vary with pressure but that’s a rider preference.

        If the casing is flexible and a cylindrical section (pretty good approximations for bicycle tires) the tension will variy directly with the pressure and radius. That means a 25mm tire at 75 psi would have the same tension as a 42 mm tire at about 45 psi. But I wouldn’t worry about casing tension other than as a limit to avoid tires blowing off or rim flanges bending.