CRR at Different Speeds: Examining Speed Dependence of Rolling Resistance

Published: 2022-01-07 by Jarno Bierman
Facebook like buttonTwitter like buttonEmail share button

We've been using our standard test protocol for all tire tests that you can find on this website since we started it in 2014. Sticking to the same protocol for all tires, regardless of their category, has given us unique data of over 200 tires that can be compared relatively easily.


We've always stuck with the standard speed of 8 m/s - 28.8 km/h - 18 mph for the rolling resistance tests, which we feel is a good compromise between road bike tires and off-road tires. As the 8 m/s - 28.8 km/h - 18 mph test speed might be a bit too low for road bikes tires and a bit too high for off-road tires, it's interesting to find out how changing speed affects rolling resistance.


This test was requested, supported, and voted for by our Pro Members. We've done speed tests at 4 m/s, 6 m/s, 8 m/s, and 10 m/s with 6 tires: Vittoria Corsa Speed G+ 2.0 TLR, Continental Grand Prix 5000 S TR, Michelin Power Road TLR, Vittoria Corsa G+ 2.0, Schwalbe Pro One V-Guard, and the Continental Grand Prix Urban. We've averaged the data from those 6 tires and made that available for free for anyone.


Pro Members can open the individual tire data and dig into the results further. We found some differences between the tires, but those might be attributed to the margin of error of the tests.


Test Set up and Conditions


We've performed all tests on the same day to get the data as accurate as possible. The load during all tests was our standard load of 42.5 kg / 94 lbs.


We usually provide rolling resistance in watts, but for this article, we will stick with the CRR (Coefficient of Rolling Resistance) values as it will be the only usable way to compare the rolling resistance at different speeds.


Our rolling resistance data never includes the aerodynamic and bearing drag of the tire and wheel combination. We measure the total wheel drag by spinning the wheel up to speed with no load applied. We also subtract the rolling resistance of the drum and wheel bearings from the total rolling resistance, which we obtain from the SKF bearing calculator. These corrections are required to get a linear response when doing tests at different speeds.


We tested at 4 m/s, 6 m/s, 8 m/s, and 10 m/s as our test machine's maximum speed is around 10 m/s. The 4 m/s test results probably aren't that usable, but the extra data point is very useful for getting a clearer picture and making it easier to extra-polate to higher speeds.


We tested only a single air pressure to make the data understandable and easily digestible. We chose 90 psi - 6.2 bars for the 25-622 tires and 60 psi - 4.1 bars for the 35-622 tire.


We used a selection of tires for the speed tests, emphasizing road bike tires. We feel the speed test results are the most useful for those tires as they are the most likely to be used at higher speeds. The MTB, CX/Gravel, and touring bike tires will probably be used very close to our standard test speed of 8 m/s - 28.8 km/h - 18 mph.


  • Vittoria Corsa Speed G+ 2.0 25-622
  • Continental Grand Prix 5000 S TR 25-622
  • Michelin Power Road TLR 25-622
  • Vittoria Corsa G+ 2.0 25-622
  • Schwalbe Pro One V-Guard 25-622
  • Continental Grand Prix Urban 35-622

Test Conditions


  • Total wheel load of 42.5 kg / 94 lbs
  • 700 x 17.8 mm wheel
  • Temperature between 21.5-22.5 °C / 71-72 °F
  • Diamond plate drum surface
  • 77 cm drum diameter
  • Excludes aerodynamic and bearing drag
  • Air pressure of 90 psi for 25-622 tires
  • Air pressure of 60 psi for 35-622 tires

Test Results - Average Results of 6 Tires


Speed Average CRR % Increase
(over previous)
4 m/s - 14.4 km/h - 9 mph 0.00346
6 m/s - 21.6 km/h - 13.5 mph 0.00362 4.6% (4.6%)
8 m/s - 28.8 km/h - 18 mph 0.00378 9.2% (4.4%)
10 m/s - 36.0 km/h - 22.5 mph 0.00386 11.6% (2.1%)
Average CRR of 6 tires at different speeds

The averaged test results clearly show that CRR increases at higher speeds. It does look like this increase is quite small, as increasing speed by 150% results in an increase in CRR of 11.6%.


It also looks like the increase in CRR is quite linear and, at least up to 10 m/s, doesn't suddenly start rising at a much higher pace. We're pretty sure extrapolating to 12 m/s can be done accurately, and we estimate the average CRR at 12 m/s to come in somewhere around 0.00393, which would be a rise of 4% over our standard test speed.


The individual test results also show close to the same results. However, the accuracy of single tire test results will be lower as the margin of error can be significant when testing only a single tire.


Test Results - Individual Rolling Resistance Data (Pro Members)


The next section is only accessible by our highly valued Pro Members. This section includes all test data of the individual tires used for the speed tests.


Conclusion


We conclude that CRR increases at higher speeds with a 150% increase in speed resulting in an 11.6% increase in CRR based on the averaged results of the six tires we tested.


We tested these six tires at average air pressures, and all tires showed nearly the same pattern. As there is always a margin of error with these kinds of tests, and the differences are small, we can't draw any conclusions about the exact CRR increase of these specific tires.


There probably are some differences between tires, and some might perform better than others. Considering the limited (average) speed range in which bicycle tires are operated, it seems these slight differences won't change the outcome of the rolling resistance tests as long as the operating speed is within 50 - 150 % of our standard test speed.


Comments