Bicycle Wheel Power Data 30km/h

Posted on 12 Comments

Over several years, bike wheels have been tested for aerodynamic performance. To date, this is the largest independent dataset available. Popular brands such as DT Swiss, SwissSide, Shimano, Mavic and Bontrager have all been tested. This dataset was originally derived from wind tunnel test data but has latterly moved over to Dinitriev number with a back calculation to give “wattage”. It is not a perfect test.

It should be noted that bicycle wheels are particularly sensitive to tire size and having a wheel and tire combination that bulges will cause a significant increase in drag. Ideally, the tire and the rim should be of the same width. These graphs are now updated on a regular basis and are plotted for interactivity. You can see some of the background for this data here.

Small differences in watts should generally be ignored as these will be affected by arbitrary things such as shoe overlap and the size of bike frame. A bigger differential will produce a bigger drop in drag but it diminishes as the wheel tends towards a disc. In general, a deeper rim will always have less drag. The spoke area which is of high turbulence is much smaller on a deeper wheel – hence the primary drag reduction.

12 thoughts on “Bicycle Wheel Power Data 30km/h

  1. It looks strange to me that a 80 mm deep rim is as bad as a 50 mm rim (Reynolds Aero vs. Bontrager Aeolus). Well, could you please show at least one digit for the wattage?

    Why did the Yoeleo Disc Rear 2018 (88mm) drop from 176 to 174 W? This is a hugh difference! The 176 W are shown here: https://www.hambini.com/wp-content/uploads/2020/09/image.png

    1. This method of testing is by no means accurate to that level and putting the decimal point down to show a difference would be akin to trying to measure the distance been London and New York in millimeters. It would be inappropriate.

      The two charts you are comparing are by two different testing systems. A large number of the back calculation is the same but not always. I hope that helps

  2. Sorry for being thick … a label to state which direction good is might help me :).

    Is bigger it smaller absorption better?

    1. less power absorbed is better.

  3. If you plot power absorbed vs rim depth the relation seems roughly linear. To be honest I would have expected to see a quadratic relation because the spoked area decreases with the square of the rim depth.

  4. Your original video for this recommended 23 or 25mm tires for best aero. Now that 28, 30 and 32 are supposedly faster due to less rolling resistance at lower pressures, is there still benefit if tire to rim width is kept in line? Personally I think the extra comfort and flat resistance of wider is worth it.

    1. This is really up to the end user. Strictly speaking, aerodynamically, inline is better but if you cannot tolerate the ride quality then you have to make that judgement call.

  5. Please add a few typical 25-30mm aluminum rims typical of a stock roubaix or domane so we can see what an upgrade could be like

  6. Hey there, it would be interesting to see a comparison of much wider rims such as the Roval Rapide CLX and the Light Bicycle WR50. The Roval are 35mm at the widest spot and are claimed to be optimized for 26mm Tires. The 105% rule is not given here. do you have any data?

    Cheers Paul

    1. Thanks for your comment, with regards the 105% rule, the general concensus in my aero circles is it should be 100%, if you can’t get 100% then slightly more is better than slightly less.

  7. Ok so you also think that the Roval Rapide CLX design is not as aero as they claim? what about wider rims in general like the LB WT50 (w: 32mm, d: 50mm)? is there a benefit in Crosswinds with a wider front rim + lets say 100 – 103% rim/tire ratio? I don´t need more comfort of a 30mm tire so im really just looking for a better handling in crosswinds. Right now im riding the LB AR56 front and rear. Im think a more U shaped rim could be better cause the AR56 have more like a V shape to them. Actual rim/tire ratio is 101% so nailed it pretty good.

    Cheers

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