Bicycle-Rolling-Resistance_schwalbe-jumbo-jim_testing-rig

No one ever says “I want more rolling resistance with my new set of tires”, but it isn’t always easy to really know what you are getting into. On road bikes it seems like there are maybe two simple questions to predict rolling resistance: is the tire expensive, and is it really light? If you answer yes to both of those, you have pretty good odds of getting a fast tire. Not guaranteed, but it’s a decent start. On the mountain bike, it seems that the correlation between high cost/low weight and low rolling resistance isn’t so clear, and when you take the leap to a fat bike, that just goes out the window.

So that’s where independent testing comes in, and no one currently seems to offer a more comprehensive list of tires with a repeatable test protocol than Jarno Bierman of Bicycle Rolling Resistance in the Netherlands. His latest round of tests pits 8 fat tires against each other to see how much 4” tires are really trying to slow you down. Check out which fat tires fare the best, and even get a look at how the real difference between butyl and latex tubes and tubeless adds up…

Bicycle-Rolling-Resistance_fat-bike-tires_results
copyrighted graphics and data courtesy of Bicycle Rolling Resistance

Looking at Bicycle Rolling Resistance‘s fat 4″ tire tests, the first thing we see is that they do generate a lot of resistance on his test drum. Sure we don’t spend much time at 18mph/29kph on our fat bikes (that is the speed he tests all tires for repeatability’s sake), but around 30-45W per tire is a lot of work to keep a fat wheel spinning. Most good 2.2″ mountain tires eat up somewhere in the 15-25W/tire range at normal pressures, and around 10-15W a piece for good road tires, so that should give a good idea of what we’re looking at.

Bicycle-Rolling-Resistance_schwalbe-jumbo-jim_chart

What you can see in the fat bike results is that tire weight is in no way correlated with rolling resistance performance. Vee’s heaviest Vee 8 comes in third overall, and pretty close to number two Fast Trak Fat from Specialized. Height of the knobs also doesn’t seem to be a big factor, as the fastest Schwalbe Jumbo Jim has tread depth in the middle of the pack. What doesn’t surprise is that casing suppleness is important. Each of the tires tested uses a high-quality 120tpi construction, which is probably critical when you are already looking at such a big tire, and the better Jumbo Jim’s 127tpi LiteSkin casing might have been enough of a difference to help it win out.

The take away from all of this is really just that different tires can make a big difference in how much energy is sapped along the way. While light tires usually offer low rolling resistance, it certainly isn’t always the case with fat bike tires. Do some quick research and you may just be able to make a sizable decrease in how much energy it takes to pedal your bike around.

Bicycle-Rolling-Resistance_tube-vs-tubeless_results

As to the tube vs. tubeless mountain bike debate, it’s no shock that tubeless is faster and that latex tubes have less rolling resistance than butyl. Manufacturers have been telling us that for years. It is of course nice to see that independent testing does confirm that, though. What is also interesting to see is that by just 55psi latex tubes and tubeless converge. While that isn’t really very important for mountain bikers or cyclocrossers (who would ever run pressures that high?!), we’ve heard a lot of industry talk about road tubeless being lower rolling resistance than even latex tube setups. So Bierman did those tests too, so hop over to his site to see what happened when he tested road tubeless tire against regular tires with tubes, all from the same manufacturer. Unlike on the trail where you can get away with converting a regular tire, for the road you really need a casing and bead that can handle the higher pressures and as you might expect that does not lead to lower rolling resistance. Now, we’ve been riding the open tubular style tubeless tire from Vittoria a good bit, and that definitely has a supple casing for a tubeless road tire. We’d really be curious to see where that fit in…

To be transparent, the above fat tire round of tire testing was actually sponsored by Wolf Tooth Components. Bicycle Rolling Resistance does work on advertising revenue from the bike industry, but like with Wolf Tooth who doesn’t sell anything even tire-related, the industry recognizes their independence and value, and other cycling companies seem happy to support Bierman’s work out of “bike nerd curiosity”. Bierman claims repeatability of his tests with a 5-10% room for error. While that might not seem to be overly precise, when you look back at the fat bike tire figures there is more than 60% variation of rolling resistance from the slowest to fastest tires, so it should get you to the right ballpark.

BicycleRollingResistance.com

39 COMMENTS

  1. It’s not the rolling resistance, it’s the additional rotational weight. .5kg in additional rotational weight will require greater energy to get up to and maintain a given velocity.

    • Where is that evident in the data? Physics says that the power needed to drive a wheel/tire system on a drum is going to be a function of rolling resistance, aerodynamic drag, and moment of inertia. Moment of inertia’s influence is going to be pretty small (you can check this at Analytic Cycling dot com).

    • The additional rotating weight will require more energy to get up to a given velocity but it will not require more energy to maintain that velocity on a flat road/trail. It will take more energy to maintain a given velocity on a climb, due to the effect of gravity, but not more than the same amount of weight located in a static, non-rotating, location on the bike.

      • They aren’t testing rotating weight, just rolling resistance. Even if they were, it won’t be anywhere near the same as they are rotating the wheel with an electric motor, not pedals. Especially when you are going uphill slowly, you will be accelerating the wheels every pedal stroke to some degree, so weight will be a bigger factor than it is in this test. The data of this test is certainly useful, it just isn’t the whole picture. Adding 100 grams to a wheel/tire combo might not make a lot of difference to most riders, but these wheels and tires add much more than that and it will be felt on a long ride.

    • If we compare the Vee 8 to the Larry, which have a small RR difference and fairly high mass difference. Accelerating from 20kph to 30kph will require 0.7w higher average power with the heavier Vee 8. You’ll note how small a difference that is in comparison to the RR differentials.

      (moment of inertia model based on same wheels and all the weight difference being at the periphery)

      The importance of tyre/wheel weight for speed is usually massively overstated. No denying that light wheels/tyres feel nice though.

  2. Pretty sure the best rolling tyre on the road market is approx 22 watts, the rest go from that up to 33 watts IIRC. So fat bikes aren’t so bad?

  3. Is it à joke? Fat tire rolling resistance tested on a slick cylinder… do they test road tires on a mud surface?
    Do they ride a bike?
    Vince, bike mechanic.

    • While the coefficient of rolling resistance does vary with road surface, tests have shown that the ranking of different tires according to rolling resistance generally does not change with road surface.

  4. Since fat bikes are never on any surface remotely like textured drum, this is kind of irrelevant in the real world no? Isn’t this just a deformation test? More deformation on snow/sand might actually be better? I can see for road, and even for mountain, but seems off as a test here.

    • There’s a large (not surprising) number of people that ride fatbikes on regular old MTB singletrack.

      That said, in the case of soft terrain, if there’s not enough traction to apply power, rolling resistance measurements are pointless.

  5. Good stuff. Those that have run everything from 1.9 semi slicks to 2.7 DH tires knows weight, width, and tread pattern can be mixed and matched to achieve results that can be counterintuitive.

  6. A rolling drum is a good indicator of a tire’s inherent rolling resistance. No matter what surface you’re rolling on there are energy losses to hysteresis (the internal friction of rubber and casing). Rolling resistance could otherwise be defined as “resistance to deformation”; therefore the slowest tires in this test are the ones which will be least supple, and least easily deform. As Cory noted in the article, often a tire being lightweight is a good indication that it will roll well, the reason for which is that a ‘thin’ piece of rubber will take less energy to flex than a ‘thick’ piece…. BUT if the rubber is not so good or the carcass material is not very pliable, then it’s like comparing a piece of plastic with a piece of rubber (obviously the plastic takes more energy to flex).

  7. Good work as usual! Loving the BRR website.

    Steel drums (smooth or textured) are brilliant for comparing tyres A to tyres B but hysteresis makes only half of the equation.
    What the test will not show is how more efficiently a 3-4″ 3-10PSI tyre rolls over stuff
    comparing the same tyre model in say 2.3″ at 25PSI… That’s where the main difference lies.

    As for extra (rotating weight)…
    From my personal and shop experience most of people worrying about it exsessivily are not exactly lighweight themselves 😉

  8. Great info but would the percentage in wattage difference be the same at a more relevant 10-15kmh for fat bike tires? I’m not too worried what’s going on at 29kmh on my fat bike as I hardly ever ride it at that speed unless downhill, but at 10kmh uphill or maybe 20kmh then I’m interested.

  9. OH MY GOD! How come making nice figures seems to be so hard for people? Why include a legend with five curves that appear exactly the same? Any person in a STEM field should have this figured out by about year two in a typical undergrad program.

    Seriously BRR – why should anyone trust that you designed a meaningful experiment when it’s obvious you don’t give a fuck about how you present your results?

    • Where exactly does it say that this is BikeRumor’s experiment? Nowhere does it say that. As for the graphs, they’re fine. The scientifically minded person will see that the plots for the tires are not the same. That same person will also notice that the behavior of the tires vs. a change in inflation pressure is qualitatively the same across tires.

      Tyler Durden, I bet if you ask nicely (and pay them to do so) they’ll provide you chart with many more data points so that you could do a nice least squares fit so that you could quantify the tires’ rolling resistance or power required to maintain a given speed vs. pressure, as well as a chart showing residuals. Would that make you feel better? I’ll bet they’ll even show error bars on their plots if you give them more money. FYI, they’re funded by their customers.

      • I think brr is bicycle rolling resistance, not bikerumor. And as someone who works in a field that relies data presentation between groups, I can say that I see a correlation between careless presentation and bad data. In that light I think Tyler’s last point is valid here.

        • The data is presented in perfectly sufficient manner, one consistent with the other data from tests at BicycleRollingResistance, and one appropriate for the audience.

  10. Thanks for all the constructive comments (good and bad).
    To the angry people…boo! Bikes are fun!

    Phil Jones and BBB got it right – this test is all about the innate rolling resistance of the tire (rubber compound, ply constuction, tread, etc). This does apply to real world riding, as the tire is constantly deflecting no matter what the terrain.

    Re Pressure, which no one asked about. We wanted a 4 PSI reading but they need to update their test equipment to a bigger motor (so Wattage numbers get really big and we suspect REALLY different between tires). Hopefully those numbers can be added at some point

    There are more test coming including tubeless vs not! Stay tuned.

    • You guys get a massive thumbs up for sponsoring this test! It says a lot about your passion and ‘nerdiness’ for bike stuff, you can consider me a new customer.

  11. Great work guys! I love dork out to this kind of bike data. To those who thought it should have been differently I anxiously await the results of your tests as well.

    • Of course cRR can different in conditions that differ from those of the test conditions. Generally, however, the ranking of a set of tires in terms of cRR remains the same when conditions change.

  12. Interesting stuff. I had some surprising results on my fat bike at weekend there. The fastest i’ve gone on my road bike down a hill is about 62.3kph (slick road tyres…110 psi) The fastest on my fat bike (4.7″ knobbly tyres…12 psi) is about 58kph. The fat bike weighs about 15kg….the road bike, maybe 8-9kg. Once you are up to a certain speed the stability and grip of a fat tyre starts to catch the road bike. Sure it takes more effort to get it up to speed but once that thing is rolling down a hill….This didn’t surprise me as much as the climbing times. I’ve climbed the same section of road maybe 11 times in varying levels of fitness. At my peak fitness & weight I did it on a 26″ Giant Anthem in 5 mins 54 seconds. 0.8km with an average 9.5% gradient (max 23%). Did the same section on my fat bike. I’m maybe 2-3 kg heavier. Did it on fat bike in 6 mins 29 seconds. This was my 2nd best time EVER! My conclusion from all that….fat bikes are not as slow as you may think. The gearing, traction and larger tyre (probably close to 29″) perhaps gave it an edge you wouldn’t expect. Watch out for the fat lad at the back.

  13. I wonder about the validity of this test. Different tread patterns could have very different rolling characteristics in the dirt. You could have a very supple casing that rolls fast on the drum, but it may have knobs that are really slow it in the dirt.

  14. Hi l have used both jumbo Jim’s and maxis mamoth tyres Jumbo’s roll much better but don’t grip as well on slippy rocks etc .rolling resistance has alot to do with type of rubber used.

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