How We Test Tires

How We Test Tires

One of the secrets behind the performance of Rene Herse tires lies in our R&D. We run our tests under real-world conditions, so we can optimize our tires for what matters: riding on real roads. When we started our research 15 years ago, high-performance tires were narrow and designed for high pressures – because that’s what makes tires fast in lab tests. In other words: The way a company tests performance determines how that company makes its tires. If your tests aren’t realistic, the performance of your tires will be compromised.

That’s why our real-world tire tests were so ground-breaking. We found that high pressures don’t make tires roll faster, that wide tires can be as fast as narrow ones, and that a supple casing is the most important requirement for a fast (and comfortable) tire. Back then, that was revolutionary, and there were no tires that met these requirements – so we started making our own. Now other companies are also offering wide tires designed to roll at low pressures, but we don’t know of any who test their tires under realistic conditions with a rider on the bike.

Performance testing of tires is complicated because it goes to the heart of the interactions between rider, bike and road surface. In fact, misconceptions about tire performance have persisted for so long because testing tires is so difficult. Even car tire makers, with multi-million-dollar research budgets, got the science wrong. When the first hybrid cars were introduced, their tires used extra-hard rubber compounds. This offered poor grip, but was thought to improve efficiency. Only recently have car tire makers discovered that tires made with softer, grippier rubber transmit fewer vibrations and are more efficient on real roads than harder tires that perform well in lab tests.

Let’s look at how tires affect the performance of a bike (or car)…

Two factors influence the rolling resistance of the bike. One is often overlooked. Looking at the photo above, you can envision these two factors.

Energy is absorbed in the tire as it flexes (hysteretic losses)
As the tire rotates, it flattens at the bottom. This takes energy – imagine squeezing a tennis ball. The less the tire flexes, the less energy it will absorb. Higher tire pressures and harder rubber make the tire flex less. That’s why we used to think that tires rolled faster if we made them from harder rubber and inflated them harder. But this overlooked an important factor:

Energy absorbed by rider and bike (suspension losses)
As bike and rider vibrate, energy is lost to internal friction in the bike and especially the rider’s body. What we feel as discomfort is actually friction between the tissues of our bodies. (In cars, the same losses occur mostly in the shock absorbers.) These ‘suspension losses’ can be very high. One Bicycle Quarterly test found that riding on a rough surface required 490 Watt more than riding on a smooth road. Both roads were flat; the bikes were the same – the difference was entirely due to the higher suspension losses on the rough road. Even on smooth roads, the suspension losses are significant. Otherwise, we wouldn’t need air in our tires, but we’d ride on rims with a round profile and just a thin layer of rubber for traction – making the tire as hard as possible. The air in the tires is essential to reduce the vibrations and the suspension losses, but this doesn’t work well if we inflate our tires too hard.

We found that it’s like a see-saw: If we inflate our tires harder, we decrease the hysteretic losses in the tires. At the same time, we increase the suspension losses. The net results is that we haven’t gained anything. If we think of energy loss as heat generation, high pressures mean that our tires stay cool, but our bodies get hot. If we only measure the tires, it appears that higher pressures (and harder rubber) save energy. But when we look at the entire system, we realize that those gains have been offset by losses elsewhere.

This is also why supple casings offer such a huge performance benefit: They reduce the hysteretic losses in the tire – imagine squeezing a soft foam ball instead of a hard tennis ball – and they absorb vibrations better, so they reduce the suspension losses, too. Racers always knew that supple casings made tires fast, but lab tests couldn’t show how great the benefit really was. That is why tire makers focused on tread rubber compounds and other ‘magic’ formulas, when the casing matters so much more.

To truly evaluate the performance of tires, we need to look at the entire system. That’s why we developed new tire testing methods to get accurate measurements of how tires affect a the performance of the entire bike.

Real-Road Testing

The only way to test the entire effect of different tires on a bike’s performance – both hysteretic and suspension losses – is by testing with a rider on the bike. Testing tires on real roads has revolutionized our understanding of tires. We found that higher pressures don’t roll faster – the increase in vibrations negates any gains due to less flex in the tire. We also found that wide tires don’t roll slower than narrow tires – at least in the size range that we ride on our all-road bikes (25-55 mm). And we found that a supple casing has a greater influence on tire performance than previously thought.

Over the last 15 years, we’ve refined our methodology. Our first tests were great for finding relatively large differences between tires – like the speed advantage of 25 mm tires over the 23s that all racers used back then. (When we shared our results with a technical consultant of a pro team, it got the ball rolling, and soon the teams moved to wider tires.)

It got a bit more complicated when we found that there was no significant speed difference between tires as wide as 54 mm and as narrow as 25 mm (with the same supple high-performance casings). What does ‘significant’ mean? With our early tests, if there was a 1% speed difference, we would not be able to determine this. And yet going 1% faster over the course of a 200-mile race can make a difference of 6 minutes at the finish! You wouldn’t want to ride 54 mm tires if 25s would get you to the finish six minutes faster – or vice versa!

So we’ve refined our methods to pick up smaller and smaller differences. Another way to increase our confidence in the results was running more tests with different methodologies. They all showed the same results: Supple tires are faster; wider tires aren’t slower; high pressures aren’t needed for performance. That way, we gained more confidence in these results.

Why doesn’t everybody tests on real roads? Real-road tests require a huge amount of effort – not in equipment, but in time. You can’t just test on any given day – you need perfect conditions with no wind and constant temperatures. We usually test just before sunrise, when there’s the least amount of air movement. In Seattle, we test during the summer months, because that’s when it’s often calm. It’s not really feasible for a big tire company to wait six months, then send their engineers to a hill at 5 a.m., finally ready to test, only to return to the office empty-handed because a very light wind has sprung up.

Let’s look at the pros and cons of some popular testing methods.

Drum Tests

The classic way to test tires is on a big drum that simulates the road surface. The power required to spin the drum empty is measured, then a wheel with a tire is added to the setup. A spring or shock absorber pushes the tire onto the drum with a force that equals the load of bike and rider. The power required to spin the drum is measured again, and the difference is how much energy the tire absorbs as it rolls over the drum.

Apart from the fact that we don’t have a rider, so we can’t measure suspension losses, steel drums have another problem: They are convex, so they press deeper into the tire than a flat road (left). That effect is more pronounced with supple tires than with stiff ones. This means that supple casings deform more on a steel drum than on a real road – which exaggerates their hysteretic losses. Supple tires still perform better on a drum than stiff tires, but their advantage is much smaller than on real roads. In other words, the casing makes relatively little difference in a drum test, but it makes a huge difference on the road.

For the same reason, low pressures make a tire much slower on a steel drum – the drum presses deeply into the softer tire. And yet on real roads, running your tires softer doesn’t slow you down. (Until the tire gets to soft that it becomes almost unrideable.)

A solution is to make the drum very large, but this gets very expensive – and you’re still not measuring the suspension losses. Basically, steel drum tests tell you to make your tires stiffer and to use higher pressures – but that doesn’t work on real roads.

When steel drum tests were popular, the tire industry moved toward stiffer casings and higher pressures, because that’s what their tests suggested. Because of these issues, many companies have now stopped using steel drums to test tire performance. They still use drums to test the longevity of their tires. Running tires on a steel drum provides a good simulation of the forces that wear them out, and it can speed up testing compared to riding tires on real roads.

In summary, supple tires perform well on real roads, but they don’t test well on steel drums, because: 
• supple tires deform more at the same pressure
• the concavity of the drum presses into supple tires more
• suspension losses aren’t measured

Roller Tests

What if we put a bike with a rider on the steel drum? We could make the steel drum rough to simulate real pavement, too… To keep a bike stable on steel drums, we need three, like the rollers used for indoor training. This limits the size of the drums: They have to be quite small, which makes them more convex (with the problems described above). If we use a commercially available roller trainer, the drums are very small, and the effect of the rollers pressing into the tires is magnified. We can feel this effect: When we stop pedaling, the rollers quickly stop, whereas we coast for a long time on a real road.

In theory, it is possible to mathematically correct for the effect of the roller’s convexity, but the correction factor will be different for tires with different stiffness. To get an accurate correction factor, we have to measure the performance of our tires on a real road first. So we end up with a circular problem: For each tire, we need accurate test results to determine the correction factor that will give us accurate test results.

Pendulum Tests

TOUR magazine in Germany came up with an ingenious test for tire resistance: They built a pendulum that rolls back and forth on a simulated road surface. The pendulum moves at low speed, so wind resistance isn’t a major factor. The road surface is flat, so there’s none of the pressing into the tires that you get with convex drums or rollers. TOUR’s team measures how long the pendulum swings, and from that they calculate the energy consumed by the tire (and hence the rolling resistance).

The speed isn’t constant, of course, so you’ll want to equalize the weight of the tires by adding weight to the rims. This seems like a promising way to test the hysteretic losses caused by the deformation of the tire. Of course, you still don’t measure the suspension losses – for that, you need a rider on the bike.

How to Design Real-Road Tests

So that brings us back to real-road testing. By using a real road, a real bike and a real rider, we are making sure that the system’s three most important parts are present. The problem is that we also have to deal with many other variables, especially wind, temperature and rider position. To get meaningful results, we need to keep these factors as constant as possible. Only our tires should change from one test run to the next – but not wind, temperature, rider position, etc. 

We’ll test on a completely calm day, because wind is never uniform – it’s always associated with gusts. Even very slight variations in wind speed will affect our results. Because rubber softens as it warms, the temperature must be as constant as possible. (It is possible to correct for temperature changes, but this introduces another variable.) The rider must be able to maintain the same position for dozens or hundreds of test runs. (We confirmed in the wind tunnel that our tester can get into the same position time and again…) And the road surface must be relatively uniform. If the rider pedals, the test surface must be perfectly flat, because pedaling even just slightly uphill requires more power than pedaling downhill, and one requirement for a good test is a constant power output.

The better we control all these conditions, the better our results will be. It may be tempting to test on a day when there is almost no wind, or to use a test track that is almost flat, but we’ll introduce more and more noise. It doesn’t take much before we can no longer discern small differences between tires. In the end, our statistical analysis (below) will tell whether we’ve been successful or not.

When all these requirements are met, tires can be tested reliably on real roads. With a rider on board, there always will be more noise than in an optimized lab setting. This means that more test runs are required to detect small differences between tires. Very small differences may be undetectable because testers run out of time before conditions change. Our goal is to fine-tune our tests so that we can detect meaningful differences. If one tire is 1% faster than another, we want to detect this. If the tire is 0.1% faster, we cannot detect this, but it doesn’t matter: It won’t change how we ride. (In any case, there is always some variation between tires of the same model due to the tolerances of manufacturing.)

For testing with a power meter, we need a perfectly flat course. A circular test course helps with time-keeping. The corners of the course must be well-defined, so the rider always takes the same line, and the pavement must represent real-world conditions. We found that the asphalt apron on the inside of our local outdoor velodrome works very well for this. A large empty parking lot might also be suitable, if it’s perfectly level. Even then, pedaling still introduces noise, because it’s difficult to keep your power output constant. We’ve used tests at the velodrome to validate the results of our roll-down tests (below) with a different method. The same tires were fast and slow in both tests; high pressures didn’t make the tires faster, etc. This gave us confidence that there wasn’t some – potentially undiscovered – systemic flaw in our roll-down tests.

Roll-down tests remove pedaling from the equation: Gravity is a constant, so the energy input into the system does not change. A coasting rider is better able to maintain the same position. And we don’t have to worry about the variability that is inherent in power meters.

The best roll-down tests are done on a constant slope, at the ‘terminal speed’ that the rider reaches when the bike no longer accelerates. A steady-state system has fewer variables than a ‘roll-out’ on a hill that ends in a flat road, where the rider slows down at the end of the test. (Wind resistance changes dramatically with different speeds.)

Finding the right hill is difficult, though. You want a hill that’s steep at first, so you get up to speed quickly. (Otherwise, you’d need a very, very long hill.) After that, you need a long stretch with a constant gradient, so you reach a constant velocity and keep it throughout your timed section. The hill shouldn’t be too steep: You don’t want to be too fast, otherwise, you’re mostly measuring aerodynamics, and small changes in rider position will affect your results more than your tires.

Calibrating Our Tests

All tests are only as good as their research methodology. We’re lucky that BQ Team rider Mark is a research expert at SAP, the global business software company. He has decades of experience designing applied research and analysis, and he’s been involved in our testing since Day 1. He’s also one of the best riders you’ll ever meet. Combined, this experience enables him to design good tests.

No matter which test method we use – laboratory or real-world – it is important to calibrate the tests to make sure nothing has changed during the course of our testing. The first step is to equalize the tire/road system. Warm rubber is softer than cold rubber, and temperature has a significant effect on how fast tires roll. Tires heat up as they roll, so it’s important to roll each tire for a while before measurements are taken. That’s important even for lab tests: Reputable labs run a tire for 10 minutes before measurements are taken. In our tests, we ride up and down the road with each new tire setup before we start testing. 

It’s also important to test in random order. For example, we should not test the tires from narrowest to widest. Otherwise, some other factor may change – for example, temperatures get warmer – and we may interpret a trend we’re seeing as “wider tires roll faster,” when it really is “warmer tires roll faster.” If we test in random order, we’re less likely to misinterpret the result “tires we tested later rolled faster.”

Testing the same reference tire multiple times is an additional safeguard. The first and last test of each session – and some in the middle – should use a ‘reference tire’ with known performance to calibrate the system. That way, we can see if conditions – temperature, wind, rider position, etc. – have changed.

Reproducibility is one key of all scientific tests: If the same test is performed twice, the result must be the same. Simply ‘testing’ four tires and reporting the results is meaningless. At the very least, one tire must be tested twice to show that the results are reproducible. Even in a laboratory setting, changes in temperature or in the measuring apparatus can affect the results. With real-road testing, demonstrating the reproducibility of the tests is even more important.

Above is an example from our most recent tests: We tested the same tires (Rene Herse Extralights) in two widths to find out whether wider tires are slower than narrow tires. We ran the bike with 44 mm-wide tires four times, then with 28 mm tires five times, then with 44s twice again. The averages are 15.47 seconds (44 mm) and 15.43 seconds (28 mm), and all test runs are within 0.51 seconds of each other.

The speed of the tests above is 27.6 km/h (17.1 mph). We ran this test at relatively high speed, because we wanted to account for the potentially higher wind resistance of the wider tires. (We run tests to determine differences between casings, etc., at lower speeds, so there is even less variability in the data.) Based on this – and many other tests showing the same – we can say with confidence that at most speeds, 44 mm tires don’t roll slower than 28s.

Statistical Analysis

Statistical analysis is a standard part of all scientific studies. It shows we’ve been successful in reducing the noise in our data. Basically, it calculates the likelihood that our results are not simply due to chance. For example, it’s doesn’t come as a surprise that the difference between the 44 mm and 28 mm tires above (0.04 seconds or 0.3%) is not statistically significant. (We checked just in case – it isn’t.) But what if we find out that one tire is 1% slower than the other? Is that a real difference, or just ‘noise’ in the data. The statistical analysis will tell us. We always cringe when somebody reports that “x is 0.78% faster/slower than y” without a statistical analysis. That’s like flipping a coin ten times, getting heads 6 times and tails 4 times, and concluding that the coin is heavier on the side with the head…

If our results are statistically significant and replicable (meaning that you run the same test again and get the same results), this also means that critics won’t be able to argue that our testing is flawed. Nobody can claim that it’s impossible to maintain the same position or that wind affected our results: The statistical analysis shows that these factors were controlled enough to reliably detect differences between tires. Statistical analysis may seem like a difficult hurdle for amateurs to overcome, but the processes are relatively standard, and you should be able to find somebody versed in them to do the analysis.

Assessing Tire Tests

Two things are essential to obtain meaningful results:

Tests must replicate the real world
If a tire test shows higher pressures rolling faster, that’s a big red flag. Higher pressures don’t roll faster – this has been shown many times and is now widely accepted. Even pros no longer run their tires at 8 bar (120 psi)… If test results don’t replicate the real world, something is wrong. (Usually, it’s that they don’t measure the suspension losses.)

Tests must be performed carefully
Running the same tire multiple times is essential, since it’s the only way to determine how reliable our data is. A statistical analysis is standard scientific practice – it allows figuring out which differences between measurements are real, and which are just ‘noise’ in the data. Reputable labs and good researchers all do this.

Conclusion

The challenge in conducting tire tests lies not in the cost of the equipment: For the most meaningful tests, we need little more than a road with a constant slope, a bike, several wheelsets, and a stopwatch. The challenge is in setting up and conducting the test: Selecting a well-suited road – most don’t have a uniform gradient. Finding a day with constant conditions – we check the weather forecast, and we’re prepared to cancel our test session if even the slightest wind springs up. And making sure the rider does not change positions during the test. This requires time and skill, but not much money. It’s also the reason why real-road tests are difficult to perform for big companies with engineers whose working hours are limited and who need to produce results on a schedule.

Tire testing can be tedious (rolling down a hill hundreds of times in the same position) and frustrating (waiting for perfect conditions can take months). I dream of buying an old, abandoned railroad tunnel in the Cascade Mountains. It would have a constant gradient of 1.5%, and being in the mountain, the temperature would never change. I’d surface it with smooth and rough asphalt, and various types of gravel, install doors (no wind!) and a sophisticated timing system, then build a cabin nearby where we can stay while testing tires. Then we could test tires at any time, without much preparation. However, the results would not be any different from what we get now with a little more patience, but much less money.

Testing tires under real-world conditions is key to developing tires that perform better in the real world. Testing our casings, rubber compounds, and tread patterns under real-world conditions is one reason why Rene Herse tires perform so well. It’s also the reason why our tires are often different from those of other makers – each tire is optimized for the tests used in its development. A tire that’s optimized for a lab test is going to be different from a tire that’s optimized by testing in the real world, on real roads, with a real bike and real rider.

In the next post, we’ll look at some results of our latest tire tests…

Further reading:

• Our book ‘The All-Road Bike Revolution’ discusses the research that has revolutionized our understanding of how bikes work: tire performance, frame stiffness, frame geometry and every other aspect that determines the performance, comfort and reliability of your bike.
• This post was adapted from a more detailed article in Bicycle Quarterly 73 (Autumn 2020).
• The results of our latest tire tests.

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Comments (80)

  • Mike

    Thank you for the detailed article. It makes sense and riding your tires, the difference on the road is really noticeable.

    March 29, 2021 at 8:42 am
  • Nate

    Great summary! I’m always surprised when I see graphs from tire makers that show tires rolling way faster at high pressures, like this one from Schwalbe
    https://www.schwalbetires.com/files/rollwiderstand_diagramm_2_en.jpg
    The 60 mm tires roll almost twice as fast at 75 psi than at 45 psi. Who’d even run a 60 mm tire at 75 psi?

    March 29, 2021 at 8:43 am
    • Ahmad Z

      I ran my 60mm g-one speed at 20.5/21psi based on Silca’s tire pressure recommendation. All good.

      March 29, 2021 at 6:33 pm
      • Jan Heine

        That makes more sense than Schwalbe’s own graphic. I wonder whether something was lost in translation on that one – even on a drum, it’s hard to see how they would come up with those results…

        March 29, 2021 at 8:58 pm
    • Mike Balloontire

      Not many would. It is clearly to compare rolling resistance between two tires of different widths (in the lab) not give a recommended inflation pressure. That pressure would produce a sidewall tension (casing tension) roughly equivalent to a 23 mm tire inflated to over 195 psi!

      March 30, 2021 at 8:04 am
      • Jan Heine

        Absolutely, but you’d still want to show an example that’s relevant for the real world.

        Most of all, I’m still at a loss for explaining that graph. Even with a drum test, you wouldn’t expect such a large advantage for a wider tire. (If a wider tire has an advantage on a drum, it would be because the contact patch is shorter, which means that the effect of the convex drum is smaller.) I suspect that if we look at the original data, there are some other issues. I’m surprised that it ever made it into the marketing materials…

        March 30, 2021 at 3:37 pm
  • Flyingbynight

    Interesting you mention car tires. Used to be that everybody said that keeping your tire pressure topped up was essential for good fuel efficiency. Haven’t heard that in a while, either!

    March 29, 2021 at 8:55 am
    • Jan Heine

      Good point! I remember many people trying to replicate the results that a slightly lower tire pressure reduced your car’s fuel efficiency, but finding that it didn’t…

      Let’s not forget that there are other reasons why you should run your car’s tires at the correct pressures, though!

      March 29, 2021 at 8:56 am
    • paulie

      Actually, I’ve found that running my car tires 5 psi higher than recommended gives me about 2 mpg better mileage. (And 5 psi less is 1 – 2 mpg lower.)

      March 29, 2021 at 6:26 pm
      • Jan Heine

        That’s what the old recommendations were, but all the carefully controlled experiments I’ve seen weren’t able to confirm this on real roads. One was by our own Alex Wetmore, who changed one variable each week (tire pressure, add a roof rack, etc.), the other was by some car magazine that went on a 150 mile round-trip drive multiple times.

        March 29, 2021 at 8:57 pm
  • Paul Lieberman

    I’m really enjoying my Humptulips Ridge on my Rawland Ravn. I’ve had Rat Trap Pass, Schwalbe Almotion, and Schwalbe Hans Dampf on this bike and the Humptulips Ridge are the best. Maybe not as fast as the Rat Trap Pass, and maybe not as capable as the Hams Dampf, but the best all around. Most of my rides are a mix of pavement and gravel so it’s nice to have tires that don’t slow you down on the pavement. Thanks for a great tire.

    March 29, 2021 at 9:05 am
    • lester g roberts

      Yes as pressures get lower the power loses grow exponentially. Think about the difference between a 5psi inflation compared to 10psi. Also 15 psi versus 30 psi. There is not a linear scale. Also depends on rider weight. The front tire on a bike can also be used at a much lower pressure compared to the front because of weight distribution. Also depends on casing of the tire. If someone told you that 70psi on car tire is more efficient than 50psi they would be wrong or if they were right it would be an insignificant point. However if they told you that a tire inflated 30psi tire is more efficient than a 10psi tire they would be right

      March 30, 2021 at 6:51 am
    • Eric Poholsky

      Very interesting article, Jan. Have you seen any performance differences between the tires with the noise reducing knobby placements and those with the original knobby placements? Also, what is the planned name and availability date for the 650B x 56c knobby tires?

      March 30, 2021 at 10:28 am
      • Jan Heine

        With the knobbies, it seems that the wider ones roll more smoothly – check out the detailed tests of the Rene Herse knobbies in the new Bicycle Quarterly.

        Regarding potential new products, we don’t usually comment until they are introduced. So I’d like to ask you to be patient a little longer, please.

        March 30, 2021 at 1:44 pm
  • Larry T

    Thanks for putting the work in to back up the long time experience a lot of us old-timers have had over the years. I got tired of telling a guy who’d just read the marketing-maven’s baloney about “Tire X” and it’s great rolling-resistance, etc… measured on a steel drum that “Wow! That’s great! When I start riding on a steel drum instead of the asphalt roads those are the tires I’ll get. Meanwhile put the fattest tires you can fit on the bike with the highest TPI and a cotton casing if you can find ’em. And don’t pump ’em up rock-hard, OK?” only to get eye rolls or talking points right off the advertising. Slowly but surely you’re proving our old-time experience was accurate, thanks!

    March 29, 2021 at 9:10 am
  • Steve

    This may be answered elsewhere, but do you detect differences in rolling resistance between slick and knobby tyres on the same carcass, e.g., RTP and Humptulips Ridge?

    BTW, it is a real pleasure to read good science explained in understandable terms.

    March 29, 2021 at 9:12 am
    • Jan Heine

      We did the same tests, back to back, with knobbies and slicks. The results are in the Spring 2020 Bicycle Quarterly

      March 29, 2021 at 9:20 am
  • Patrick Stuart

    I wonder if it would be possible to program an e-bike to run the test without relying on a hill. Set the e-bike to a constant power output or constant speed and measure the resulting speed or power, respectively. If that doesn’t provide enough power or speed, then maybe it would be possible to target the total output (battery plus rider, with battery power varying to accommodate with fluctuations in human power) or the speed of the combined boost and rider power.

    March 29, 2021 at 9:13 am
    • Jan Heine

      That’s an interesting idea. You’d have to set up the ebike to have the same riding position as the bikes you’re interested in. And then you’d need to make sure the ebike’s motor doesn’t get hot, otherwise its efficiency might change. Gravity has one huge advantage – it’s constant!

      March 29, 2021 at 9:22 am
  • Guy Jett

    A suggestion for a modified test protocol:
    • A flat surface (road, velodrome, parking area, etc.).
    • Windless day.
    • Same bike / position.
    • An electric bike!

    Either
    • Set the power at the same rate and measure the resultant speed, or
    • Set a uniform speed and measure the power consumption.
    • Always start with the battery at or near full charge.

    Advantages:
    • May be easier to find venues with variable surfaces.
    • Greater ability to test at various speeds.

    Disadvantage:
    • Greater cost?
    • Possible variance in power output / speed as battery is used.

    Respectively,

    March 29, 2021 at 9:30 am
  • George Valiquette

    How do you measure your times to the nearest 0.01 seconds in your timed interval tests?

    March 29, 2021 at 9:39 am
    • Jan Heine

      We use a stopwatch. That obviously introduces some error, but it averages out with multiple tests. We’ve thought about a more sophisticated timing system, but it wouldn’t add much precision to the results. There’ll always be some noise in the data, mostly due to very slight changes in rider position and very slight air currents. Minimizing those is more important than reducing the last 0.05 seconds in timing error. (Even in the Olympics, hand-held stopwatches were used until the 1960s.)

      March 29, 2021 at 9:53 am
      • Mark Pitts

        This is the most worrisome statement I’ve read on your testing protocol.

        For this 15sec test – was this a rolldown test or velodrome?

        Human reaction time is on the order of 200 milliseconds-ish? Where is the person standing as a viewpoint? If a rolldown, the middle of the start/end points? At 17mph and 15sec test, thats ~188 feet to either side! That’s not a good perspective for reliable timing.

        I would more readily ignore the hand timing if the total test time was large enough to absorb timing error as noise…but 1% of 15sec is 150 milliseconds. Given there will be accumulation of other small variabilities, I’m worried you won’t get any meaningful comparison.

        March 30, 2021 at 6:06 am
        • Jan Heine

          Human reaction time is on the order of 200 milliseconds-ish?

          That’s a misunderstanding. If you are surprised by something, human reaction time is 0.2 seconds. (For example, a car in front of you brakes.) But if you see the cyclist approach the finish line, you can time much better than that, because you don’t react to the cyclist suddenly appearing at the finish line, but your eyes pan along until they cross that line. Otherwise, all results of the Olympic Games before the 1960s would have to be thrown out because they were timed with hand-held stopwatches.

          Beyond that, the statistical analysis shows that there isn’t much variation in the timing. Even if the entire 0.5 second variability we got in our test of 44 mm vs 28 mm tires was due to timing error – unlikely, since rider position and air currents will affect the results as well – this wouldn’t change our results.

          One reason to do many test runs is to have all those errors average out. That’s how medical research is done – human subjects make it difficult to control variables, so you just test more people. If you have one person getting healthy after taking a new medication, it doesn’t tell you anything. But if you have 5000 people take the medication, and 5000 take a placebo, and 70% of the medicated people get well vs 30% of those who took the placebo, you can say something with more confidence (if the statistical analysis supports this). Again, that’s why statistics are so important.

          March 30, 2021 at 8:11 am
          • Mark Pitts

            Yes, good point on the anticipation. I am still very skeptical of relying on human timing since humans are unreliable, and not just noisy but possibly biased (no intention implied). A genuine timing system would remove doubt and strengthen your results.

            I agree with the point on lots of samples to find trends within the noise. How many times do you test? The graph shows 10 samples which intuitively doesn’t seem to hit the large numbers needed. Do you have the full dataset and statistical analysis available?

            Note I am not coming from the perspective of trying to deny your hypothesis, I am just interested in having the strongest body of evidence. I prefer wider tires myself, using 35mm Bon Jon’s on my “fast” bike, and want to feel better knowing I’m not giving up much of anything in pursuit of comfort 🙂

            March 30, 2021 at 11:02 am
          • Jan Heine

            As Mark pointed out earlier, these findings have been replicated many times. First we tested 20, 23 and 25 mm Michelin Pro2 Race tires in our intial rolldowns. Then we ran Compass Standards 26, 28 and 32 mm tires on the track with a power meter. Then we tested all types of Rene Herse Extralights between 28 and 54 mm on the track. In our most recent tests, we ran 28 and 44 mm tires both at high and low speeds. There are multiple datasets – and all show the same: Wider tires don’t seem to roll significantly faster than narrow ones.

            I’d say that we’ve got the greatest confidence with our latest tests (28 vs 44 mm), whereas the power meter tests have a bit more noise. So it’s possible that a 54 mm tire is (very slightly) slower (or faster) than a 44, but we can say for sure that a 44 isn’t slower (nor faster) than a 28, at least at speeds that most cyclists ride. We could extrapolate to high speeds, since there is no difference in behavior between low and moderately high speeds, which indicates that there is no difference in aerodynamics, either. But we’re cautious when we interpret our results, so we leave that up to you.

            The biggest issue here is that all this could be specific to rider and bike. We tested on 3 different bikes, so again, there’s no indication that we tested an outlier. The most recent tests were on a Salsa Warbird with Enve aero wheels.

            Compared to other data you see – like the very strange Schwalbe graph that another commenter mentioned earlier – I think this is the best and most carefully done test you’ll find.

            March 30, 2021 at 1:57 pm
  • Carey Gersten

    After rolling with the Oracle Ridge on my Specialized Diverge for several months, I replaced them with a set of well respected 38mm gravel tires. Not bad, but after a couple of months I put the Oracles back on. Jan knows his stuff. They’re staying on!

    March 29, 2021 at 10:07 am
  • John Halunen

    Very much agree with the testing, but it seems like the definition/description of your suspension losses may be inaccurate? It is quite possible the loss of energy is simply due to moving the entire bike/rider up and down small amounts (instead of internal friction in the muscles)? Or more likely some combination of both? Has anyone worked to figure that out? It would have to produce heat in the body, but isolating that…

    March 29, 2021 at 10:30 am
    • Jan Heine

      There’s some old research from the 1960s by the U.S. Army on tank seats that identified the suspension losses – they found that human bodies could absorb up to 2000 Watt before they stopped the testing because their subjects found it too painful. They also found that perceived discomfort and energy absorption in the human body were directly related. So yes, your body does heat up. If you ride on cobblestones, you can actually feel your muscles getting warm!

      The idea that the bike moving up loses energy – sort of like climbing micro-hills – has been proposed by some people, but it doesn’t really work that way: You get that energy back as the bike comes back down – especially with pneumatic tires, where the tire pushes off the backside of the bump. (On mountain passes, you don’t get the energy back because wind resistance is greater at the downhill speeds than at climbing speeds.)

      March 29, 2021 at 10:37 am
  • Prabuddha Dasgupta

    The tests are interesting. It is good to know that they are done so painstakingly in real world conditions. I have one question. As tires get wider, considering the same kind of casing, they would get heavier, would they not? So considering that I’ve been riding on 28mm tires mostly on smooth to broken asphalt, at what tire width would I start feeling the weight penalty of the wider tire? My preference for wider tires is mainly for the puncture protection of low tire pressures.

    March 29, 2021 at 10:59 am
    • Jan Heine

      Wider tires inevitably get heavier, but the tests factor all this in already. It’s easy to calculate the effect on acceleration – we did that for our book The All-Road Bike Revolution. In the real world, wheel weight is much less important than most cyclists think.

      March 29, 2021 at 12:36 pm
      • Prabuddha Dasgupta

        Thank you for your reply. I have just ordered your book. I am severely constrained in my experimenting with tires here in India, owing to availability. Shipping can be a real dampener.

        March 31, 2021 at 2:27 am
  • Jim G.

    ALL my bikes (and I have too many) and my wife’s bikes (she also has too many) have your tires on them now. We don’t race, we just ride. Enough said.

    I would have liked to have seen a time for a 23mm name brand tire @110lbs for comparison. I’m never going back, I’d just like to know.

    Jim

    March 29, 2021 at 11:06 am
    • Jan Heine

      We did that way back in 2006 – it was slower than a 25 with the same casing. That started the entire ‘revolution.’

      March 29, 2021 at 12:37 pm
  • Stuart Fogg

    Have you tested at different speeds? I’m curious if the power varies linearly with speed (constant force) or some other way.

    March 29, 2021 at 11:13 am
    • Jan Heine

      We test at low speeds to isolate rolling resistance, and at moderate speeds to factor in wind resistance. Testing at high speeds isn’t feasible, since you’re looking at wind resistance above all. So if you want to know how much difference tires make at high speed, you’re better off calculating that based on the values you get for crr at low and moderate speeds.

      March 29, 2021 at 12:45 pm
  • Stuart Fogg

    Have you tested rubber compounds with different hysteresis (as opposed to hardness)? If so have you seen differences in the test results?

    March 29, 2021 at 11:15 am
    • Jan Heine

      We’ve tested a variety of rubber compounds, and we’ve chosen the ones that roll fastest for our tires. Fortunately, they also offer excellent grip. Recently, we investigated some of the latest polymers that test so well on steel drums with a view of changing our tread rubber. So far, we’ve found them to offer no advantages…

      March 29, 2021 at 12:46 pm
  • Mark Guglielmana

    Pretty much all of this has been written in BQ before, but this is the best synopsis of everthing we now know about tire performance that I’ve seen. I’ll link to this article in the future for non-believers.

    With the wide range of diameters and widths now available, it’s clear to me that one should choose the tire first, then build the bike around it – rather the opposite of what we used to do!

    Well done!

    March 29, 2021 at 11:34 am
  • Marius Clore

    I don’t think you made clear how you account for differences in tire pressure between narrow and wide tires.
    For example, the 44 mm tire would probably be run at say 35 psi, while the 28 mm tire would probably be at 60 psi (if both are tubeless and setup without tubes).

    Thus, I would suspect that a 28 mm tire run at 30-35 psi would perform rather badly but would do well at 60 psi. On the other hand, most rims might not be able to take (or at least it might be unwise) to run a 4 mm tire at 60 psi.

    The other thing I would add is that your test time (15-16 sec) is very short and therefore makes it hard to pick up significant differences, especially when slight changes in body position on any descent may have a much larger impact on speed due to aerodynamic resistance from the rider.

    March 29, 2021 at 12:02 pm
    • Jan Heine

      We tested tire pressure separately, and we found that it has little effect on rolling resistance. So we ran each tire at a pressure that comes out to a similar tire drop. For the 44 mm tire, that means 30 psi, for the 28 mm, we tested at 65 psi.

      Regarding the length of the test, since the speed is constant, it doesn’t matter how long the timed section is. Where it matters is with the measurement error due to timing with a stopwatch at the beginning and the end of the test. For our low-speed tests, we have a longer run (30-40 seconds, depending on the tire), so we get a little more accuracy.

      March 29, 2021 at 12:53 pm
  • Greg Miners

    Do you measure atmospheric pressure too? Relative humidity?

    March 29, 2021 at 12:08 pm
    • Jan Heine

      For most tests, we test a reference tire immediately before and after the new tire/setup. That means we’re doing a relative comparison – the new tire/setup is xx% faster/slower than a known tire. That means that temperature, atmospheric pressure, relative humidity don’t affect the results. That’s better than measuring all these factors and then trying to correct for them.

      March 29, 2021 at 12:55 pm
  • Tom G

    It’s great to test in the most lifelike conditions possible and I really like the ride of your tyres. However, to strengthen the arguments presented here you could:
    a) take a range of tyres already subjected to drum testing by you or someone else and demonstrate that your testing returns different results in terms of the relationship between them.
    b) systematically investigate the effect if casing, tread compound and tread mass upon measured speed
    c) compare your tyres with other market leaders using your testing protocol
    d) find better ways to quantify dimensions of tyre performance such as grip and puncture resistance which may be traded off against speed.

    It’s all very well insisting that you have a superior testing protocol but do you have any data that compares your tyres against other popular products?

    March 29, 2021 at 12:13 pm
    • Jan Heine

      Those are good points.
      a) Back in 2006, our first tire tests looked at tires that tested well on drums, and we found that some (supple hand-made tires) tested well on the road, too, while others (ultra-high pressure, hard rubber) didn’t. We also tested different tire pressures, expecting them to make a difference on the road. They didn’t. You can find all that in our book ‘The All-Road Bike Revolution.’
      b) Again, we did that. All our tests weren’t simply tests of ‘Is tire A faster than tire B’ but ‘What makes a tire fast.’
      c) Again, we’ve done that. We’ve been a bit reluctant to publish results that show our tires being fastest, but we’ll do that in the next post.
      d) That one is tough. Nobody has figured out a good way of testing grip, except riding tires. I think most riders will agree that ours are among the most grippy you’ll find anywhere. Puncture resistance is hard to test, too. The standard test of hitting the tire with a needle and counting how long it takes to puncture doesn’t really say much – in the real world, most tires puncture after multiple revolutions hammer the debris deeper and deeper into the tire.

      March 29, 2021 at 12:43 pm
      • Tom G

        Thank you for your detailed reply. I intend to read your book when I have a moment, and your BJP in extra light casing is still the nicest ride quality I’ve ever experienced on a bike.

        I’m looking forward to seeing more data. Specifically, I find it hard to believe that some of the new polymers would not make a significant difference given the strides made in drum testing metrics over the last decade by the leading players. You have written before that you deliberately include a decent (3mm??) tread thickness; however even the Veloflex Record, a tyre with an extremely supple casing and barely a smear of tread, has just achieved a significant reduction in drum tested CRR after updating the compound.

        I would be extremely interested in head to head comparisons of Continental GP5000TL 700x32c and Continental Terra Speed 700x40c with Rene Herse tyres of matched section. For bonus points using a variety of casings to demonstrate the tradeoff between durability and speed, and/or a file tread vs knobs to show the cost of the latter.

        March 30, 2021 at 2:37 am
        • Jan Heine

          We tested some of the new polymers – they aren’t trade secrets, and we could use them, too. However, on real roads, they were actually somewhat slower, and the difference was statistically significant.

          This reminds me of our first tire tests. We included the Vittoria Open CX Corsa – a traditional hand-made tire back then – and the Michelin Pro2 Race – a tire with a stiffer casing, but ‘optimized’ (and relatively hard) rubber compound. (This was in 2006.) Both tested the same in a steel drum test done by TOUR on Continental’s equipment. In our real-road testing, the Open CX rolled much faster than the Pro2 Race. In fact, the Pro2 Race was no better than Conti’s similarly harsh-riding Ultra-Gatorskin. It appears that drum tests also give erroneous results when testing tread compounds.

          As to testing all the tires that compete with our tires, we obviously can’t do that – we’re more interested in optimizing our own tires than comparing them with others. For a comparison on TOUR’s pendulum between our Standard casing with Conti’s then-current GP, check out this post. Obviously, their method doesn’t test suspension losses, but I don’t think anybody would claim that the Contis roll smoother than Rene Herse tires. The new Contis might roll a bit faster (if they improved the casing) or slower (if the new rubber only tests well on a drum), but our Extralights certainly roll faster than the Standards that TOUR tested.

          March 30, 2021 at 7:55 am
          • TomG

            I’m struggling to come up with a mechanism by which a polymer that showed lower hysteresis losses on a drum could be slower in real life, if the amount of rubber, casings and puncture belt were exactly the same. I would have thought suspension losses were mainly determined by the air pressure.

            For sure, the first time I tired Vittoria Open Corsas it was a lightbulb moment for me in terms of comfort, feel and (I thought) speed. But drum testing found them to be no quicker than Conti GP4000 which was tougher, longer lasting, grippier in the wet and cheaper. (NB this would have been circa 2009, I think the real progress was made when Conti introduced their “Black Chili” compound.

            Your tyres are more expensive in my region than heavily discounted Contis – surely it would be good for your sales if you could demonstrate, albeit with in-house testing, that your tyres were unequivocally the fastest option on the market? I’d certainly be happy paying a premium for that performance.

            I’m still in the camp that feels drum testing is sufficient to rank tyres and that the key after that is in finding the right pressure as per Tom Anhalt’s graphs, and then taking aerodynamic considerations on board.
            But there is precious little inter-brand comparative real-world testing out there and if you have the data I’m sure you would be rewarded handsomely with sales.

            March 30, 2021 at 8:23 am
          • Jan Heine

            The mechanism why rubber compounds that work well on drums often don’t work well on the road is the same as with air pressure: On real roads, you want the tire to conform to the surface and not transmit vibrations. Skateboarders have known for decades that softer rubber wheels roll faster, yet I’m sure that on a drum harder wheels would test better.

            There are other aspects of tire performance that a smooth drum cannot detect. For example, a very fine tread appears to roll faster than a slick tire, probably since it can deform slightly without ‘activating’ the entire casing.

            The idea that drum tests can provide a ranking of tires has been disproven by our real-road tests. The Pro2 Race scored exactly the same as the Open CX Corsa on the drum, but in the real world, there was a large difference between them.

            March 30, 2021 at 9:12 am
          • Tom Anhalt

            Wait…so your opinion on the validity of drum testing is based on a single comparison of 2 tires, using a drum test done by someone else (so not the EXACT same tires) and compared against a somewhat error prone “field test”? That doesn’t seem very “scientific” of you.

            BTW, have you ever done a Crr version of the “Tom Compton Challenge” to determine the sensitivity of your Crr evaluations? One way to do that would be to keep tires/pressure/position constant and vary mass (such as empty vs. full water bottles)? This works because, by definition Crr = Retarding Force/(mass x gravity). In other words, if you assume mass is constant in your calculations, but actually change it, what’s the equivalent change in Crr your method detects?

            March 30, 2021 at 10:53 am
          • Jan Heine

            I’m not sure what to make of your comments here. The validity of drum tests or lack thereof isn’t an ‘opinion,’ and it’s not based on just a random comparison of two tires. The biggest issue – and we’ve talked about that for 15 years now – is that drum tests show higher pressures rolling faster. There are two mechanisms at play here: 1. drums don’t measure suspension losses and 2. drums are convex, so they press deeper into the tire than a flat road. Both these mechanisms mean that a tire that’s inflated harder (and hence stiffer) deforms less and has less resistance on a steel drum.

            In the real world, we found that higher pressures don’t make tires faster. We tested this many times, with different methodologies, with different tires and on different bikes. We also identified a mechanism why that is the case: Lower pressures decrease suspension losses, which counters the greater hysteretic losses.

            We’ve also identified a number of tires that tested differently on steel drums and on real roads. That includes not just the Open Corsa CX and Pro2 Race mentioned earlier, but also the Ultra Gatorskins and the Deda Tre Giro d’Italias. We also found that the ‘tubular disadvantage’ is much smaller in the real world than in a drum test. All these results are consistent with the observation that drum tests don’t measure suspension losses and that the convex shape can be an issue.

            Regarding detecting the difference between full and empty water bottles with respect to Crr – I doubt you can reliably detect that. I know that your tests claim to detect incredibly small differences, such as the aero effect of a different front brake or a small disc attached to the bike to change the frontal area, but I find that hard to believe with tests on real roads, with wind and other noise in the data. Again, I want to see a clear mechanism why and how you can detect small differences that can’t even be detected in a wind tunnel, where all factors are controlled as closely as possible. Simply fitting a curve and saying “See, it matches!” doesn’t mean that you’re actually measuring real phenomena.

            March 30, 2021 at 3:34 pm
  • Ron Thompson

    As a retired Army civilian vehicle system engineer and analyst, I can confirm the routine use of “passenger absorbed power” as a measure in the Army Mobility Model. And as a life long cyclist, and now as a recumbent bicycle developer, I fully support your analysis, test, and evaluation. Bike rider absorbed power is a big deal.

    I have become a big fan of your Snoqualmie Extralight 44mm 700c tires. They have proven to be fast, comfortable and handle great. After about a thousand miles on a conventional upright bike and on my “all road” recumbent, I have no problems with flats and they appear durable.

    I don’t often publicly engage, but am all about better bikes for more people. These tires are part of that.

    Thanks.

    March 29, 2021 at 1:18 pm
    • Jan Heine

      “Passenger absorbed power” is an interesting concept. I can imagine that if you put a dozen soldiers in the back of a stiffly sprung Army truck, the difference may be noticeable.

      March 29, 2021 at 1:30 pm
  • Brian Biggs

    @Jan – First, thanks for making bikes not only faster but more fun and comfortable!

    Quick question: I’ve recently been trying to improve my PR on a 25 minute climb. My daily tire is a 700x38mm Barlow Pass (tubed) @ 40psi. Just for fun, I put on my old Conti GP4000 700×28. @ 80psi.

    The Conti felt much more satisfying climbing out of the saddle and I wondered if this has to do with less tire compression / hysteretic losses? Even the smoothest cyclists are going to send more force straight down when climbing out of the saddle.

    Since you’re trying to measure real world riding, have you ever tried to factor in pedaling out of the saddle?

    You might need another abandoned railway tunnel @ 8% 🙂

    Thanks.

    March 29, 2021 at 2:26 pm
    • Jan Heine

      We tested the hysteresis due to pedaling thrust when we rode on the track with a power meter. Even at very low pressures, it wasn’t significant. (We didn’t pedal out of the saddle, as it’s almost impossible to maintain the same position when doing it.) You can test that yourself – just inflate the Barlow Pass 38s to the max. pressure. They’ll deflect much less, and you can see whether that makes your bike feel like it does with the 28s.

      What I suspect you are seeing is the heavier weight of the bigger wheels making the bike harder to rock the bike from side to side. That’s why many of us prefer smaller 650B wheels with wider tires, and 26″ with even wider tires.

      March 29, 2021 at 8:55 pm
  • John E McClain

    I’ve been part of “passenger absorbed power” every time we went somewhere in a deuce and a half, or six by, thirty or so Jarheads in the back of the truck on wood benches. The deuce and a halves were substantially easier on the bones. I’ve been riding near on fifty years, only recently came to realize, because of your testing, I’ve never road a “a fat tired road bike, but am going to have to do as was commented above, buy a set of tires, build a pair of wheels, and build a bike around them. I’ve got two or three road bikes, all narrow 25’s or so, but I’m convinced. I worked avionics in the Marines twenty years, saw several thousand radios or navigation gear, of a dozen different types, along with multitudinous other “same repeat equipment” and your road tests demonstrate the same capacity for repeat performance that taught me the dynamics inside “rf cavities” and such, and I am thoroughly convinced. I’ve been following your testing of tires, because I was rather surprised, and had to read through half a dozen of your tests, as I ran across your site a few years back. I really enjoyed reading all the feedback, and hope to enjoy some more comfortable riding.

    March 29, 2021 at 6:10 pm
  • Ahmad Z

    Jan, thanks for the excellent article. Do you think there is a diminishing return beyond 55mm in efficiency and rolling resistance? Can I assume that MAY be the reason why you limit your tires at 48mm and 2.2″ wide? I hope I’m wrong cos I love the rebellious look of riding against skinny tires with the roadies.

    March 29, 2021 at 6:43 pm
    • Jan Heine

      The main reason to stop at 55 mm (we offer tires wider than 48!) is that it becomes hard to fit the tires between road cranks that help with a good spin. I also think that for road riding, you reach a point of diminishing returns. But I can tell you that riding my Firefly with its 55 mm tires with roadies doesn’t seem to slow me (or the bike) down.

      March 29, 2021 at 8:59 pm
      • Ahmad Z

        Excellent. Please offer the 55s for the 650Bs.

        March 29, 2021 at 9:31 pm
  • Tom Anhalt

    I think you misunderstand the value, application and validity of roller testing.

    You say that roller testing, and especially small roller testing, doesn’t reflect “reality”…and yet, “the proof of the pudding is in the tasting”, and many comparisons of Crr values measured on small diameter rollers show that they are well calibrated to what is seen in carefully conducted field testing. One example is shown here from Andy Coggan from over a decade ago. http://www.trainingandracingwithapowermeter.com/2010/06/crr-roller-vs-field-test-results.html You’ll see that aside from an offset due to the difference in surface roughness between the 2 test conditons, the slope of the line fit is basically “1”. This matches my own personal data.

    As long as pressures are kept below the breakpoint pressure for Crr, then small roller testing is an extremely valuable way of judging the rank order between tires.

    BTW, I have YET to find a “stiff” tire that performs better than a tire with a more flexible casing on small roller (4.5″ diameter tests). Your speculation on that matter is a bit off-base. A tire that performs poorly on the road due to a stiff casing, high compound losses, excess “armoring”, etc.) will perform just as poorly (by the same percentages, in fact) on a roller test.

    Roller testing is an easy and accurate way to evaluate hysteresis losses. Evaluation of what pressures result in dramatically increasing “suspension” losses (i.e. the breakpoint pressure), requires a bit more work, but it’s fairly easy to avoid those pressures, once one realizes that it’s far better to err on the side of “too low” of pressure, than “too high”.

    BTW, Tour Magazine didn’t come up with that pendulum rig on their own. I recall reading a research paper over a decade ago from a collegiate HPV team that described the pendulum method in quite a bit of detail. It’s a clever approach, but I have concerns about the “stop/start” nature of the testing. It would be interesting to see a correlation similar to what I linked above from Andy Coggan on that method.

    March 29, 2021 at 6:51 pm
    • Jan Heine

      “the proof of the pudding is in the tasting”

      That’s not how science works. If you get the ‘right’ result despite clear shortcomings of your method, this doesn’t mean that you’ve magically overcome those shortcomings. So if your drum or roller tests don’t show a strong correlation of rolling resistance and tire pressure – unlike all other drum tests and despite a clear mechanism of why that usually is the case – then that doesn’t validate your methodology. On the contrary, it raises the question why your drum tests have different results from all others.

      You also seem to misunderstand – supple casings do perform better on drums and rollers, too, but their advantage is much smaller than in the real world. And since supple casings don’t support high pressures, it means that stiffer casings (at higher pressures) appear preferable when you test on drums or rollers. On real roads, the advantage of supple casings is much greater, and there’s no advantage to high pressures, hence the answer to the question ‘What makes a tire fast?’ is very different.

      March 30, 2021 at 3:20 pm
    • Jacob Musha

      The blind, ignorant skepticism in this thread is astonishing. I’ve never seen any other real-world testing of bicycle tires aside from Bicycle Quarterly, and you’re giving Jan all the flack? Give me a break. Do your own testing (verified in the real-world, of course, and supported by statistics) if you don’t “believe” these results.

      I really can’t believe people are still looking at drum testing today. The flaw is so obvious: a smooth steel drum would test faster than any tire. Put some steel drums on your bicycle and see how it rides.

      March 31, 2021 at 6:44 am
  • David Loyd

    One aspect of tire performance that one might further explore is the correlation between propensity for flats and tire tread. I’ve noticed since the advent of mountain bikes that larger, knobbier tires get fewer flats. On my 1-hour commute through glass-strewn streets, cheap 700c x 32 Paselas with no kevlar protective strips but newish tread work about as well as the ones with the strips. And 650 x 42 Hetres, with their increased volume and prominent tread ridges, seem to work better than smaller or smoother-tread tires at not picking up wire and glass fragments. Lightweight, supple, large-diameter tires with a few mm of tread could have both a good ride and flat protection when run with tubes. Perhaps that simply means using knobbies, but there may be other tread patterns that are supple, lightweight, quiet, and offer this sort of flat protection.

    March 29, 2021 at 7:58 pm
    • Jan Heine

      A real-world test of flat protection (rather than a lab test that doesn’t tell us much) is very difficult to do, because flats are both rare and random. You’d have to randomly switch between two sets of tires on hundreds or thousands of rides, ideally on the same course. Over that period, weather would change (temperatures might affect flat resistance), you’d have to throw out runs with wet roads (water acts as a lubricant and makes the rubber easier to cut), and the amount of debris might change with the seasons.

      So we’re left with anecdotal evidence and engineering. Engineering tells us that if we put a puncture-proof belt in a tire, it’ll help ward off flats from glass and thorns, which get crushed before they can work their way through the belt, but not from steel wires, nails and sharp rock slivers, which just take longer until they penetrate the belt.

      The idea that the knobbies have more rubber in some places and voids in the others also makes some sense. I can imagine the debris getting pushed into the voids between knobs as the tire rolls over it. Unless the debris is very large, it’ll do little harm when it’s in between the knobs. The change that debris hits a knob right in the middle is relatively small, so your chances of a flat are much reduced. (The same reasoning made some people suspect at first that narrow tires will have fewer flats, since they touch less of the road surface. But the higher pressure of narrow tires makes them easier to puncture, and that factor appears to be far more important.)

      Another approach is to wipe off the debris before it gets lodged in the tire by installing tire wipers.

      March 30, 2021 at 7:37 am
  • MikeB

    It would strengthen everything you have reported here if you would publish your ANOVA. I have not seen, for example where the mean squared error variance if greater between tires than within. With the means that are reported, I would expect the number of runs per condition would have to be a big number in order to demonstrate clear statistical significance. Can we see your actual stat results? You will not shut up the skeptics until you have reported those.

    March 29, 2021 at 9:31 pm
    • Mark Vande Kamp

      I’ve been involved in most of the tire research and have conducted the majority of the analysis. In the past, we’ve published the statistical methods used in the research and they aren’t exotic in any way and they haven’t changed. I wish that skeptics were so easily silenced that publishing an ANOVA result would do it. As I’m sure you know, inferential statistics are used to test hypotheses in ways that are tricky to explain without technical language that most readers are likely to find confusing, boring, and strangely non-committal. If the text says there is a difference between tires, then we found a statistically significant difference. Do flukes happen – sure they do, but many of these findings have been replicated multiple times. Repeated testing has consistently supported the validity of the basic conclusions about casings, tire width, and air pressure. Is it possible that there may be very small differences between, say a 28 mm and a 44 mm tire that our test didn’t detect – sure, it’s possible, but we’d need to test hundreds of tires across hundreds of runs in order to detect differences that are so small that they are meaningless to real world riders. Data have noise in them. Statistics are a tool to make a structured argument that there is a real signal in the noise. We used the tools correctly.

      March 30, 2021 at 1:46 pm
      • Jan Heine

        Thanks for chiming in, Mark. The original statistical analysis was published in Bicycle Quarterly 19.

        March 30, 2021 at 3:17 pm
      • Nate

        It’s not like other bike companies publish their entire dataset or statistical analyses…

        March 30, 2021 at 3:53 pm
  • Isha

    This is another great and complete article on the subject and I don’t dispute any of the major claims. However in the bit under ‘Energy absorbed by rider and bike (suspension losses)’ you say the 490 extra watts are all due to suspension losses. I would imagine the hysteretic losses are also increased somewhat on rough roads.

    Another thought I had is that an indoor test facility with a ramp on one side and multiple types of road surface should not be too difficult or expensive for the big companies to set up. There would be no wind and the temperature could be controlled.

    March 30, 2021 at 2:42 am
    • Jan Heine

      You are right – hysteretic losses probably go up when the road gets rough. I should have written that the entire 490 watts are due to the road roughness.

      Regarding indoor testing facilities, it would be useful. But buildings are expensive, and in reality, most engineering even at big tire companies goes into keeping production running smoothly, not figuring out how to make their tires faster. That’s why pro racers still buy their own FMB tubulars for races where they really need every advantage, despite (or because of) FMB’s production methods being very low-tech. (Their tubulars are amazing, though.)

      March 30, 2021 at 8:00 am
  • Gary Long

    Hi Jan! Just a quick general question about your René Herse 700C / 29” tires: In all but one of the wider models (both knobby and smooth treads), the standard casing and endurance casing versions weigh more or less the same; the one exception is the 700C x 44 Snoqualmie Pass TC (375 g vs 425 g). Why is this?

    March 30, 2021 at 4:02 am
    • Jan Heine

      There are many reasons. Some of it is inherent to the Snoqualmie Pass. The tread is relatively thin – it’s the narrowest of our wide tires – but for the Endurance, there’s a little more rubber. Part of it is simply variations between tires and production runs. The last run of Standards turned out a bit on the light side (less rubber on the sidewalls), the Endurance is a bit heavier than it used to be. The main thing that affects a tire’s speed is the casing. More rubber does make it a bit slower, but the difference isn’t enough to make a measurable difference: We tested the Snoqualmies in Standard and Endurance, and their speed was the same.

      March 30, 2021 at 3:43 pm
  • Chris Grigsby

    Jan, have you ever tested the detriment of low pressure on climbing out of the saddle? I run low pressures on my BSP ELs as I ride a lot of mixed terrain, but I do wonder when I can clearly see my front tire bobbing up and down as I climb a steep gradient out of the saddle how much time I’m losing as a result?

    March 31, 2021 at 7:48 am
    • Jan Heine

      Climbing out of the saddle is hard to measure, because there are many variables. It also depends on riding style – rocking the bike from side to side flexes the tire less than bouncing up and down. Overall, when climbing a steep slope, rolling resistance probably isn’t very important, as most of your energy goes into gaining elevation.

      I think a bigger factor is whether the flex in the tire helps or hinders you in developing power. That’s something you can experiment with – just try different tire pressures and see how it affects your climbing.

      March 31, 2021 at 9:08 am
  • Richard P. Dunner

    What is nowwhere mentioned is the influence of higher weight in the circumference of the wheel??!!! Is there no influence? In other words, for example for 700C, a 25 mm tire, weight 250 gr, A 28 mm tire, weight 300 a and more gr. A 35 mm tire 350-400 gr? This + obviously a rim old style 420-450 gr, (20 mm wide), new rim 480-550 gr. (23-28 mm wide). This means, a difference in the outer wheel weight of lightest rim 420 gr + tire 250 gr + tube 70 gr, total 740 gr. to heavier rim 500 gr + tire 45 mm 450 gr (up to 800 gr) + tube 150gr total 1,1 kg

    I would appreciate your opinion or test results.

    March 31, 2021 at 8:28 am
    • Jan Heine

      The testing includes all those factors – we’re testing real tires on real bikes on real roads. You can also calculate the influence of wheel weight on acceleration. We did that in our book ‘The All-Road Bike Revolution’ and found that the effect of lighter wheels is smaller than most cyclists think.

      March 31, 2021 at 9:10 am
  • Chris Grigsby

    Probably a topic for another article, but you recently stated that tubeless tires don’t have lower rolling resistance than butyl tubes and that latex tubes can actually double the benefits of Extralight casing. How can a latex tube take less energy to deform than liquid sealant?

    March 31, 2021 at 11:24 am
    • Jan Heine

      Liquid sloshing around apparently has more hysteresis than a very flexible latex tube that deforms just a little where the tire touches the groun.

      April 1, 2021 at 10:08 am
  • nellborg

    Jan, I have Barlow Pass’s in EL and Snoqualmies in Endurance casing. The Barlow’s feel much softer and more comfortable than the Snoqualmies – particularly over the light gravel roads that I ride. This is over a range of 25-38 psi and knowing that an apples to apples comparison would have the Snoqualmies a few psi lower.

    From reading much of what you’ve written and what Josh Portner has offered, I have bought into the idea that “smooth is fast” with regards to tires and tire pressure. Therefore, I am convinced that my Endurance casing Snoqualmies must be considerably slower than my EL Barlows – because if I can feel the difference then the difference must be real and significant.

    If that’s the case, and that I’m feeling increased hysteresis from the Endurance Snoqualmie’s, are they significantly slower than the EL Barlows? Or is it just that the ride “quality” is different? Or is it all in my head?

    March 31, 2021 at 12:48 pm
    • Jan Heine

      You are right, the Extralights are faster – that’s why we make Extralights and don’t just all ride Standard or Endurance casings. The difference is noticeable, but it’s not huge. Stay tuned, we’re working on a Journal post that shows the actual measurements. (The full story was published in the Autumn 2020 Bicycle Quarterly.)

      April 1, 2021 at 10:11 am

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