Bicycle Wheel Power Data 30km/h

Posted on 28 Comments
winspacehyper

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.

28 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

  8. Will you run a test on the FFWD F4R FCC wheels ? very interested to see if the DARC profile actually directs flow away from spokes. Seems like a good hypothesis.

    1. Only if a set is sent to me

  9. Is the power absorbed figure on a “per hour” basis ? I doubt that, but how can I apply this data to an hour of riding ? Perhaps how much drag is added from a theoretical constant of zero drag ? or some such thing. Flo Cycling stated that on of their wheels reduces the amount if time ridden over 40km by 1 min 12 seconds ( I don’t know at what speed). That did not seem that impressive to me, and made me think of all the training I need to do to reduce my time ridden by 5 minutes over 40 km.

    Still, it would be fun to get a pair of Winspace wheels. I just want to know how to translate “power absorbed” into some kind of time benefit over distance or an hour period at a theoretical constant speed.

    1. Power absorbed is by definition the amount of energy in one second. 1Watt = 1 Joule per second. You are right the drag saving is small compared to training hard but it’s pay once and reap the benefits purchase. I hope that helps.

      1. So if the x-axis is watts ? Then the Winspace Hyper wheels absorbed 182 watts per second ?

        1. at 30kph.

        2. Nope. It’s 182 Joules of Energy per second which is equal to 182 Watts.

  10. so the difference between say – Mavic Kysrium 2027 is about 13 joules ? Multiplied by 60:seconds is 780 joules? Multiplied by 60 minutes is 46800 joules ?

  11. sorry to be blogger from hell, after al long day at your real job. try to think of beatrice. Rolling resistance is measured in watts per hour by Jarno at bicyclerollingresistance.com. This figure is generally between 10W and 20W. Let’s say 10W/hr for now. That is .0028:watts per second. (joules, yes thank you) Very trivial compared to aero resistance.

    Now I am asking you to be a math checker ! Is that better or worse than having to teach luddites fluid dynamics ?

    1. I’d rather teach luddites

  12. All very good but how many watts does it take to spin the wheels???

    1. that depends on how fast you are going.

  13. Hi, i am currently riding yoeleo 38mm carbon profile with alloy brake surface (1600+ gram) within areas of mix flats/climbs.

    Hyper rim 65mm is 1500+ gram
    Hyper rim 50mm is 1350+ gram

    Which is considered a significant upgrade, 50mm or 65mm? Both hyper are still lighter than my Yoeleo C38, thus climbing wont be an issue for both i think.

    Is 50mm considered too small of an upgrade from 38mm for aero/all rounder purposes but HUGE gain in weight saving?

    Does upgrading to 65mm is a waste since not much of a weight saving from current Yoeleo C38 carbon alloy but better aero profile?

    1. You need to go for the deepest rim that you can ride. 65mm would be an improvement on 50

      1. You mean 65mm a better (significant) upgrade instead of 50mm with all the weight consideration from current yoeleo carbon alloy 38mm?

  14. Borg 50C looks like the best all around wheel, especially for its price. Sure there are Yoleo, Winspace and the rest, but I don’t trust the long shipping from China to EU.

    That said, what is the best option for alloy rim brake wheels?

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