Myths Debunked: Higher Tire Pressure is NOT Faster

Myths Debunked: Higher Tire Pressure is NOT Faster

This used to be one of the first things you learned as a cyclist: If you want to go fast, make sure your tires are pumped up to the maximum pressure. The harder your tires are inflated, the faster they roll.

We now know that this is not true. The realization that tire pressure does not affect performance is the key to the revolution that has swept through the cycling world in recent years. Without this new-found knowledge, all-road bikes and their supple, wide tires would make no sense at all. Here is how it works.

Shortcut: If you just want to know how much to inflate your tires, our tire pressure calculator allows you to optimize your tire pressure for the lowest rolling resistance.

Tire resistance is determined by two factors:

Hysteretic Losses: With each turn of the wheels, the tires flex. You can see that in the photo above: Both tires flatten where they touch the road. Flexing the tires takes energy – imagine squeezing a tennis ball. Energy on a bike can only come from one source: the rider’s power output. Reduce the energy lost to flex, and you’ll go faster.

The easiest way to reduce this energy loss: Inflate the tires more, and they’ll flex less. Less flex means less energy is converted to heat as the tire casing deforms under the weight of bike and rider.

You can also reduce the losses by making the tire casing easier to flex. A supple casing is easier to flex than a stiff one, so it absorbs less energy for the same amount of flex. Imagine squeezing a marshmallow instead of a tennis ball.

So we want a tire that is supple and runs high pressures. That means we have to make it narrow. Why can’t a wide tire be supple and run at high pressures?

Pressure is force per surface area. For example, PSI stands for Pounds per Square Inch. The larger the tire’s circumference (more inches), the more force will act on it (more pounds). Imagine the casing as a chain, with the pressure as an elephant standing on each link. If the chain is ten links long, it has to support the weight of ten elephants. Make the chain twice as long, and you’ll have twenty elephants standing on it. The chain has to be twice as strong. Or you have to reduce the weight of each elephant. Back to tires, this means that a wider tire either needs a stronger (read: stiffer) casing, or you need to reduce the pressure.

Summary: The best way to reduce hysteretic losses is to use supple tires, make them narrow, and inflate them hard. With wider tires, you either can have a supple casing or high pressure, but not both. Either way, wider tires will have more hysteretic losses. If you only look at hysteretic losses, ‘wide high-performance tires’ seems like an oxymoron.

That was the accepted wisdom when we started looking at tire performance way back in 2006. It’s not incorrect, but it overlooks a second factor that also affects how fast a bicycle rolls – and tire pressure works the opposite way there.

Suspension Losses: As the bike vibrates, energy is lost. Most of that energy is absorbed in the rider’s body, as soft tissues rub against each other. Decades ago, the U.S. Army studied tank seats and found that the discomfort we feel from vibrations is caused by friction between our body’s soft tissues. This friction consumes energy that is turned into heat. (Rub your hands against each other to see how friction creates heat.) The more uncomfortable the vibrations, the more energy is lost.
Mountain bikers have known for a long time that bouncing makes your bike slower. The fastest mtb is the one that absorbs shocks best. Road cyclists used to think that we had to ‘tough it out’ to go fast. We endured the discomfort of narrow high-pressure tires because we thought that they rolled faster. We thought that pavement was too smooth for suspension losses to matter.

At Bicycle Quarterly, we started to test the performance of tires on real roads in 2006. At first, we also assumed that higher pressures rolled faster. However, as long-distance cyclists, we suspected that there was a point of diminishing returns. Our thinking was this: In a short race, we may endure all kinds of discomfort if it makes us faster. But we can endure discomfort only for so long before it affects our power output. In a ride as long as the 1200 km (750 miles) of Paris-Brest-Paris, we might give up 5% in rolling resistance if we gain 20% in comfort. What we wanted to know: Where is this point of diminishing returns?

Back then, tire resistance was tested on steel drums that measure only the hysteretic losses. On steel drums, there is no doubt that higher pressures produce better results – as shown by all tires in the table above. Take the Vittoria Rubino Pro (second from bottom): At 60 psi, it requires 40% more energy than at 120 psi. I mention this tire, because later on, you’ll see how it performs under real-world conditions.

Drum tests also suggest that high pressure is more important than a supple casing: In the table above, the slowest tire at 120 psi has less resistance (13.4 W) than the second-fastest tire at 60 psi (13.9 W). That is why tire makers used to make their wide tires with stiff casings, so they could withstand high pressures. A wide, supple tire – limited to a low pressure rating of, say, 60 psi – would perform poorly on the steel drum. That is why they didn’t exist – who would want to make a slow ‘high-performance’ tire? It all made sense – if you tested your tires on steel drums.

Imagine our surprise when we found that in the real world – on real roads – tires perform very differently. We tested numerous tires, with two different methods (roll-down and power meter), and always found the same: Higher pressures don’t make tires faster.

We also found that the advantages of supple casings are much larger than the steel drum tests suggest. Why? Because the suspension losses are significant even on very smooth roads. And both lower pressures and supple casings reduce the vibrations of the bike and thus the suspension losses. But you cannot measure suspension losses unless you have a rider on the bike. That is why earlier studies (and many since) failed to give meaningful results…

Above are the real-road results for three Vittoria 700C x 25 mm tires, including the Rubino Pro. We tested on brand-new, ultra-smooth asphalt. For the Rubino, there is no difference in speed between 80 and 110 psi. It’s clear for all three tires you see here: Higher pressures don’t make them faster. (Note that the watts are for the entire bike and rider, not just for one tire. That is why the power measurements is so much higher than in the drum tests.)

What happens is this: As tire pressure increases, the tire flexes less, and the hysteretic losses go down. However, the tire also vibrates more, and the suspension losses increase. The two roughly cancel each other, and that is why there is no clear trend in the table above.

Before we continue, it’s important to mention that we made sure these results are statistically significant. This means that we are seeing real differences in performance, not just ‘noise’ in the data. (Our data analysis is performed by Mark Vande Kamp, who has a Ph.D. with a minor in statistics.)

The graph shows a few more things:

  • Really low pressures make a tire slow, because it flexes way too much: the hysteretic losses are huge. The extreme is a totally flat tire – extremely slow. At some point, the tire has enough air to avoid excessive flex. Above this ‘break point,’ hysteretic and suspension losses start to balance each other.
  • Hysteretic and suspension losses are non-linear, so they balance differently for different tires and different pressures.
  • CX Tubular: A tubular tire sits on top of the rim, so it can flex around its entire circumference. It can run at very low pressures without excessive flex. The break point is low (80 psi).
  • CX Clincher: A clincher rim constrains the tire around about 1/3 of its circumference, so higher pressure is needed to avoid excessive flex. The break point is a bit higher (87 psi).
  • Rubino Clincher: The Rubino’s stiffer casing is harder to flex: The hysteretic losses for the same amount of flex are higher. The stiffer casing also transmits more vibrations, so low pressure doesn’t reduce the suspension losses to the same amount. This means that the break point is higher than for the more supple CX (95 psi).
  • All three tires roll slowest at moderately high pressure: The tire is already too hard to absorb vibrations, so suspension losses are high. However, the casing still flexes, so hysteretic losses are also high. It’s better to run low or very high pressures, at least on the very smooth asphalt of our test track.

Summary: On real roads, even smooth ones, higher pressures don’t roll faster.

We tested many tires – above from our first tests in 2006 that measured the time for a roll-down on a carefully chosen test hill – and we always found the same: Above the break point, increasing the tire pressure doesn’t make you faster. The break point is higher for stiffer tires. For the tubulars, the break point is lower than the pressures we tested.

I wish we had done this testing when I was still racing. Back then, I ran 21.5 mm Clement Criteriums at a bone-rattling 130 psi. I would have been faster – much faster – on 28 mm Campione Del Mondos at much lower pressures.

What if we go to really high tire pressures? We ran a 25 mm tire all the way up to 200 psi, and it didn’t get any faster. (Don’t try this at home, it’s not safe to run these tires at that pressure!)

The above results were on ultra-smooth pavement (Vittoria) and relatively rough, but not bumpy, pavement (others). Does the road surface affect a tire’s break point?

To test the extreme, we ran various tires on rumble strips, which are a good stand-in for cobblestones. (Unlike real cobblestones, rumble strips are very regular, so we could obtain repeatable results.) We also tested each tire on the smooth pavement right next to the rumble strips.

On the smooth pavement (left), the Compass/Rene Herse 26 mm tires roll as fast at 75 psi as they do at 95 psi. This confirms what we’d found before: Even on smooth roads, tire pressure makes no difference.

On the rumble strips (right), higher pressure was slower: The 26 mm Compass/Rene Herse tires used 20% more energy at 95 psi than they did at 75 psi.

Summary: On really rough surfaces, higher pressures roll slower. Wider tires roll faster on rough surfaces because they can handle lower pressures.

So now we know that higher pressures don’t make your bike faster – whether on ultra-smooth asphalt, on rough surfaces like cobblestones, or anywhere in between. For supple tires, the break point – even on smooth surfaces – is close to the point where the tire becomes unrideable, because the sidewalls collapse under hard cornering. On rough surfaces, it’s hard to reach the break point – the tire pinch-flats before its performance deteriorates.

Conclusion: If you want to go fast, you need supple tires. That is all. Pumping them up harder won’t make you faster. On rough surfaces, it actually makes you slower.

When we saw these results, we realized that this could revolutionize bicycles: If we didn’t need to high pressure to go fast, we could make wide tires with supple casings, run them at low pressure, and still roll as fast as we did on narrow ‘racing’ tires. With these wide, supple tires, we could go on roads and trails that wouldn’t be much fun on a traditional, narrow-tire racing bike.

We envisioned a new breed of bike – racing bikes with ultra-wide, supple tires – and we called them ‘Allroad Bikes’ (still without a hyphen). That was way back, in 2006.

Then we set out to turn this new type of bike from a dream into reality. The first step was to make the tires we needed for these all-road bikes. First we worked with other manufacturers, but in order to get exactly the tires we wanted, we introduced our own tires in truly wide widths (above). It’s taken the bike industry a little while to get on board, but now our ideas are generally accepted: all-road and gravel bikes are the most important segment in the performance bicycle market.

All-road bikes are more than a passing fad, because they finally correct one of the shortcomings of traditional performance bikes: the need to trade comfort for speed. Now we know that discomfort not only is unpleasant, it actually slows you down. Put more simply:

Comfort = Speed

Cycling has become much more fun on all-road bikes that combine the fun of riding a performance bike with the comfort and go-anywhere ability of wide tires. They are the bikes of the future, and they are here to stay.

Tire Pressure Calculator:

• Our tire pressure calculator helps optimize your tire pressure for the lowest rolling resistance.

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Comments (35)

  • Jacob Musha

    I’d be curious to see power tests done on gravel. There are lots of “gravel” bikes and “gravel” tires out today that are still in the 33-38mm range. I don’t even want to run those widths on pavement anymore! I’m almost certain my 52mm Rat Trap Pass tires are faster, but that is still difficult for folks to grasp.
    In any case, I’m very thankful for the service Bicycle Quarterly and Compass have done. Keep up the great work!

    January 3, 2019 at 7:54 am
    • Jan Heine, Editor, Bicycle Quarterly

      Testing on gravel is something we’ve thought about a lot. The difficult part is finding a uniform gravel surface. If you hit bigger and smaller rocks with each test run, the results are not comparable. That is why we tested on rumble strips. In the end, most gravel surfaces are somewhere in between the rumble strips and the smooth asphalt. So the results are easy to predict: You’ll be slower on higher pressures. How much slower depends on how rough the gravel is.

      January 3, 2019 at 3:26 pm
    • Samuel Atkinson

      It’s counterintuitive, but with Rat Traps, I’ve found that my mixed-surface ride advantage over those 30-40mm gravel tires is actually most distinguishable on the pavement.
      “Skinny” gravel tires need to be run at more extreme drop than fat tires to achieve sufficient squish on rough surfaces. And, due to the smallness of the tire and the more extreme drop, they end up exposing their sidewalls more to the riding surface. To solve the sidewall exposure, people use beefier tires with tougher sidewalls… which combines with the extreme drop to considerably increase rolling resistance.
      Rolling advantages certainly matter on rough surfaces, but they can be obscured by the effects of handling and confidence. On the road, it’s laid more bare. If there’s someone that I’m competitive with when we’re both on traditional road bikes, but they’re having to put out huge watts to even stay in my draft on the paved portions of mixed-surface rides on our gravel bikes, something is going on.

      January 3, 2019 at 3:47 pm
  • Matt Meko

    One thing I’d be interested to know more about is tire pressure effects on climbing out of the saddle. I know that (low) pressures that feel great otherwise can become immediately noticeably sluggish out of the saddle on a steep climb.

    January 3, 2019 at 9:22 am
    • Jan Heine, Editor, Bicycle Quarterly

      You are right, once the tires get close to the point of collapsing, they’ll be slower. However, you don’t want to run a pressure that low anyhow, as the tires also can collapse during hard cornering. The ‘low’ pressures we are talking about here are still high enough that the tire doesn’t flex excessively when riding out of the saddle.
      When I ride on gravel, I run lower pressures, and there, the bike does feel squishy when climbing out of the saddle on smooth roads. That is why I increase the pressure if there is a long paved section ahead. If it’s a race like the Oregon Outback or the Volcano High Pass Challenge that combine pavement and gravel, I try to judge the pressure so it works on both surfaces.

      January 3, 2019 at 3:29 pm
  • Bob

    Jan, I appreciate all of your testing and analysis. However, I don’t see anything in your graphs to relate bicycle speed to tire performance. In other words, it looks like your testing was done at a speed of 17 mph. For slower riders (average 13-15 mph), I would suspect the performance gains would fall off, and the losses due to vibration would be less.

    January 3, 2019 at 10:26 am
    • Jan Heine, Editor, Bicycle Quarterly

      The most important part at lower speeds is that wind resistance becomes much smaller, and tire resistance makes up a greater portion of the overall resistance. So faster tires actually offer a greater benefit for slower riders.
      As to the suspension losses, it really depends. The rumble strips were almost unrideable at lower speeds. At high speeds, you have enough inertia that the bike no longer falls into each depression.

      January 3, 2019 at 3:32 pm
  • Phillip Cowan

    Jan, there is no doubt in my mind you have done a great service to cyclists everywhere. Your rigorous scientific testing has slain a few sacred cows when it comes to tires. Do the tests, collect the data and let the chips fall where they may no matter who doesn’t like it. I love it!
    I wish you would turn your laser beams on the issue of “foot retention”. For example is a rider on pinned platforms really giving up anything to a rider in clipless or even clips n straps. It’s long been my suspicion that the guy on platforms is at no disadvantage and as a benefit he never has to walk in clunky shoes.

    January 3, 2019 at 10:47 am
    • Jan Heine, Editor, Bicycle Quarterly

      Others have studied foot retention, and we’ve looked at it, too. On flat terrain and even speeds, flat pedals are all you need. Nobody seems to pull up consistently on the pedals. Sustained power comes from the downstroke.
      However, during accelerations or on short hills, most riders do pull up on the pedals. That is why we tend to pull out of pedals with toestraps unless they are really tight. Riding with platforms in Seattle was really a big adjustment for me when I tried it: I had to downshift for every small rise, rather than just pedal harder (and pull up on the pedals) for a few strokes. So I think it depends on your riding style, but for spirited riding, foot retention is definitely useful.

      January 3, 2019 at 3:36 pm
      • marmotte27

        Foot retention is also useful on descents I think. It’s safer to have your foot fixed on the pedals when you hit 40 or 50 kph or more.

        January 3, 2019 at 5:31 pm
      • Mike

        We must have different riding styles. I have no problem pedaling harder uphill, even for sustained climbs, with regular shoes and platform pedals. My feet don’t leave the pedals. I don’t think that foot retention is universally useful for such cases.
        As for downhills: why would foot retention matter, unless you’re riding a fixed wheel? When the pedals just don’t stop moving, keeping your feet lashed to the pedals sounds like a good idea. In all other cases, where you have the ability to freewheel downhill, what’s the point of foot retention?

        January 4, 2019 at 7:08 pm
      • Phillip Cowan

        From studies I’ve seen it seems the brain is neurologically wired for push-push and not push-pull although it certainly possible to teach the legs to pull up on the back stroke. The perception of test subjects doing the push-pull pedal stroke is that they are putting out more power but the instrumentation invariably says otherwise.
        I’ve noticed a lot of “serious” bikes on the internet showing up with pinned flats (especially bikepacking rigs). Most of this trend is probably driven by the fact that wearing cleated shoes out in the boonies is kind of a drag but some owners have commented that they don’t feel like they’re losing anything.

        January 5, 2019 at 6:51 am
  • Kim

    Great article!
    I am curious: What pressure do you ride Jan Heine? (and rider weight + tires)

    January 3, 2019 at 1:04 pm
    • Jan Heine, Editor, Bicycle Quarterly

      I ride 650B x 42 mm tires at about 40 psi on the road, about 30 psi on gravel. With 54 mm tires, I use 35 psi on the road and 25 psi on gravel. Weight of bike, rider and luggage is about 90 kg (200 lb) at the start of a long ride.

      January 3, 2019 at 3:38 pm
      • marmotte27

        Underneath on of your articles on tire tread/longevity of tires I mentioned the inner half of the filetread on your tires wearing away on my LoupLoup Pass. You answered that I seeemed to ride the tires at lower pressures than recommended. Now I see that I run higher pressures than you all the time. I tend to be on around 2.7 -2.9 bars on the front and around 3.3-3.5 bar on the rear. Even if the pressure runs low, I’m never below 2.5 on the front and 3.0 on the rear.
        The low pressures you run on gravel are unimaginable for me. I’d have punch flats all rhe time. What am I doing differently (wrong)?

        January 3, 2019 at 5:43 pm
        • Jan Heine, Editor, Bicycle Quarterly

          Different pump gauges can read very differently. My 40 psi may read 30 or 50 psi on your pump gauge. Joshua Poertner talked about this – when they tested tires and pressures for the pros sponsored by Zipp, they found that the three pumps they had in the support car all had wildly different readings. Fortunately, for the rest of us, the absolute pressure isn’t so important – just find a pressure that feels right, and continue to use it.

          January 3, 2019 at 7:30 pm
    • Mike

      Regarding pressure gauges: I suspect that the gauge on my floor pump is no more or less accurate than anyone else’s. It scales up to at least 130 psi so it makes sense to me that it is less sensitive at the lower pressures that I/we use on wide and supple tires. That’s why I bought a small tire pressure gauge from the local car parts store. This gauge goes up to only 60 psi which makes it more sensitive to lower pressures. I hope that it’s more accurate than the pump gauge. 20 psi on the floor pump typically reads 25-27 psi on the car tire gauge.

      January 4, 2019 at 7:14 pm
  • Monty Richardson

    Thank you Jan. Since I first read your research I have continuously talked to people about this – many unbelieving. Last year, a young lady, with 25C @110lbs almost came off her bike on a rough pavement downhill. I had her reset her tires at 75-80lbs and there was instant improvement in her speed, comfort and confidence.

    January 3, 2019 at 1:26 pm
  • Axel Reichert

    Many thanks for another great summary post to be forwarded to the remaining stubborn racers. For the numerically inclined: Hysteric losses have been analyzed by Peter Appeltauer (a theoretical physicist and former Mercedes Formula One engineer) in his (German) tome about “The small print in cycling”. With a system mass of 80 kg and an “uneven” road (only 0.5 mm amplitude, 10 Hz frequency) he quotes a US Army source from 1966 with surprisingly large losses of 12 W. The 0.5 mm refer to the amplitude that remains AFTER the tires have done their suspension work. On real roads, I strongly doubt that a 23 mm tire at 0.8 MPa will achieve such a small amplitude. I think this fits nicely into your observations. If needed, I can provide the details regarding his book/sources.

    January 3, 2019 at 1:32 pm
  • Anthony MIlls

    Jan, swapping to the Babyshoe 42mm tires was a super improvement in comfort and handling, and my choice for long endurance rides. However, when racing, the weight and width of the tire are significant contributors to speed compared to a 25mm GP4000 (700C). The tire’s weight (rotational kinetic energy) and narrowness (aerodynamics) being factors. I have found that for the same bike and effort (200W power), I am 1.5 -2.5kph slower on the Babyshoe compared to the GP4000. This difference increases significantly when racing. As a suggestion, perhaps your article should address these factors and conditions as well.

    January 3, 2019 at 3:58 pm
    • Jan Heine, Editor, Bicycle Quarterly

      Interesting – this doesn’t match my observations. On my randonneur bike, I have no trouble keeping up with riders on racing bikes. The rotational inertia is the same, whether you run a big wheel with a small tire or a small wheel with a big tire – that is why the handling doesn’t change. As to aerodynamics, it’s not significant. We tested in the wind tunnel both 25 and 31 mm tires, and the results were in the noise. A cyclist’s aerodynamics are almost entirely determined by frontal area, and even a 42 mm tire isn’t much wider than a modern bike’s down tube. If it mattered, we’d be way faster on classic steel bikes with smaller-diameter tubes…
      However, this doesn’t mean that there isn’t something else going on. We’ve found that tire pressure can change how a bike feels and responds. On some Bicycle Quarterly test bikes, wider tires at lower pressures greatly improved the performance – the bikes ‘planed’ because the tire could provide the needed flex. If you prefer a stiffer frame, then the wider tires may have too much give for optimum performance. Try inflating them harder and see whether this changes that impression.

      January 3, 2019 at 7:18 pm
      • Stuart Fogg

        I’m one of those who prefers a stiffer frame and I climb out of the saddle a lot. My total load is just under 200 lbs and I think the 38 mm Barlow Pass XL tires are best around 60 psi. I found wider tires need almost that much pressure or they start feeling squirmy, so for my preferences anything wider and softer is past optimum.

        January 4, 2019 at 12:18 pm
  • kai

    agree with your findings with supple tires Jan, and nice that you had the strength to get through what happened after opening this pandora’s box. it must feel good to be on the other side.
    of course this knowledge isnt new, they surely lived after these principles in the 30s and 40s with the so called balloon tires. we have such bikes left in our family and they are a charm to ride on gravel. what happened with that hype i think might have had to do with the market beeing flooded with heavier look-alike bikes with cheaper and stiffer tire options – that were not supple!
    was definitely not good for the reputation of such bikes. unfortunately such a demise can repeat itself also this time.

    January 4, 2019 at 4:43 am
    • Jan Heine, Editor, Bicycle Quarterly

      Absolutely. In fact, we were inspired to check out wider tires by the stories from the riders on René Herse’s team, who raved about the wide, supple, handmade clinchers of the 1940s. Those trace their ancestry back to the wide tires that Vélocio popularized in the 1920s.
      I had heard about the German ‘Ballonreifen,’ but never got to try one. As roads got better and tourists took their inspiration from racers, the knowledge about wide tires almost got lost…

      January 6, 2019 at 6:16 am
  • Conrad

    Any plans on testing a tubeless versus standard setup? Sometimes I wonder if adding a bunch of liquid to your tire doesn’t slow it down.

    January 4, 2019 at 9:24 pm
    • Jan Heine, Editor, Bicycle Quarterly

      The liquid most definitely slows the tire down. See also this post. We also tested this, running a set of tires tubeless with the absolute minimum of sealant, and with tubes. The speeds were indistinguishable. Once you add enough sealant to ride reliably, the tubeless setup will be slower.
      Tubeless is great when there is a risk of pinch flats. The sealant can also help with punctures from goatheads that are the bane of cyclists in some regions. But it doesn’t make you faster.

      January 6, 2019 at 6:20 am
      • Mark Guglielmana

        Jan, sure it does (sealant makes you go faster). Less time on the side of the road fixing flats = higher average speed.

        January 6, 2019 at 8:06 am
        • Jan Heine, Editor, Bicycle Quarterly

          Last year, I got exactly one flat tire in all my urban, suburban and cross-country riding. When I think back to the days of narrow tires…

          January 7, 2019 at 6:01 am
  • Eli Torgeson

    Jan, do you think your research applies equally to suspension losses induced by the rider? I am not sure that I am saying this properly. Instead of the road trying to rob power from the cyclist, can the uneven power output of the rider, in certain situations, lead to more losses in more supple tires at low pressure? They scenario I am imagining is climbing out of the saddle. Is the energy used to deform the supple casing at a low pressure being taken from the overall powerful output of the rider? Would a stiffer tire in such a scenario fare better? Alternatively, is there evidence that the energy can be returned to the forward motion of the bike in another phase of the pedal stroke: tire planing?

    January 5, 2019 at 9:33 pm
    • Jan Heine, Editor, Bicycle Quarterly

      We wondered about this, which is why we tested with a rider pedaling in addition to our rolldown tests. I’m sure that if you run such low pressures that your tire collapses with each pedal stroke, you’ll increase resistance, but the bike also won’t be safe to ride around corners. With normal tire pressures, you won’t lose enough to tire flex when riding out of the saddle to make a difference. There are other reasons why riding out of the saddle is less efficient than climbing seated, though…
      As to ‘tire planing,’ that is definitely a factor. We’ve observed that on numerous test bikes with very stiff frames and wide tires. By dialing in the tire pressure so that there was just enough flex, the bikes performed much better for us than they did with higher pressures.

      January 6, 2019 at 6:23 am
      • Steve

        That has been my experience too. It suggests to me that planing might be less about energy being returned to the drive train and more about flex (either in tyre or frame) offering feedback to the rider enabling them to pedal ‘better’ i.e. to apply power at the most appropriate moment of the pedal stroke.

        January 6, 2019 at 10:39 am
        • Jan Heine, Editor, Bicycle Quarterly

          That is an interesting idea. However, the energy from the tires will be returned to the drivetrain the same way as it is when the rear triangle flexes.

          January 7, 2019 at 6:05 am
  • Mark Guglielmana

    Throw out all of the testing data, all of the comparisons on performance of wide vs narrow, lower pressure vs higher pressure, and you’re still left with one fact. The comfort of riding a wider, suppler tire on a long ride means I get beat up less on rough roads. Living in the PNW as you do, Jan, we have the joy of miles and miles of beautiful forestry roads devoid of cars to ride on. In the last 5 years I’ve gone wider and more supple with my tires, and my enjoyment of riding on gravel has increased as a result.
    The interesting thing I’ve noticed is that my bikes with 650b x 42 and my bike designed around RTP tires doesn’t slow me down on smooth pavement – when I can find it! Typically that’s only in the suburban environment I live in, where stop lights don’t allow for much sustained riding at speed…

    January 6, 2019 at 8:15 am
  • Mischa

    Hi Jan,
    this article is a great source on one of the hottest topics still up till now. However there is one question I have. Shouldn’t it be possible to confirm your observation on more laboratory kind of tests, for example instead of rolling the tire on a big steel drum use something more asphalt/gravel like? Like on a treadmill with a more uneven surface.

    January 6, 2019 at 12:27 pm
    • Jan Heine, Editor, Bicycle Quarterly

      The observations have been confirmed with numerous tests, on the road. We’ve thought about lab testing on some sort of drum. (Treadmills have too variable drag to produce good results.) To fit a bike with rider on the drums, they have to be small. But small drums dig into the tire – a problem that gets worse with low pressure and supple casings, basically anything that makes the tire less stiff. The way around that is to make the drums very large – at least 1 m (3 ft) – but then there is no way to construct a roller that can fit a bike. Perhaps one could build an extra-long bike, but it all gets very complex only to confirm something we already know.
      Steel drums are still used for other testing, like the longevity of tire treads and the UV-resistance of rubber as it flexes. However, performance testing on steel drums is pretty much a thing of the past, since the results aren’t very meaningful.

      January 7, 2019 at 5:58 am

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