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Bicycle Wheel Power Data 30km/h

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.

Warning

A number of cyclists get infatuated by very small differences between the wheels. Guidance in this regard is to adopt a 2.5SF rule. That is to say that for an appreciable difference, there should be a difference of 2.5 significant figures.

eg a rider is unlikely to notice a difference between a 190W wheel and a 180W wheel (2SF). There is some error in there as well as geometrical differences based on the rider and their bike. When the difference becomes 190W vs 175W, that is effectively 2.5SF and would be noticeable.

This is a rule of thumb and requires considered application as it converges at slower speeds. There is a larger spread at higher speeds.

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45 Comments

    1. Hello, if I send you my Mavic iO, would you add it to your test? Also, I’ve had people comment that my iO is on backwards. There is a sticker on my iO indicating direction of travel, so unless Mavic put the sticker on backwards. The model is 2015 year so before the Rio model.

    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

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

    Is bigger it smaller absorption better?

  2. 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.

    1. Yes but the outer part of the spoked area is travelling faster than the inner part, and aerodynamic drag is quadratic with velocity.

  3. 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.

  4. 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

  5. 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.

      1. By “slightly more” do you mean the rim should be slightly wider than the tire (ala 105% rule) or that the tire should be slightly wider than the rim?

          1. How much is slightly? + or – .5mm? E.G. 25mm Michelin Power TT measure 27mm on Yoeleo 88mm (26.6mm wide at rim) a difference of .4mm so would that be equal(same width)?
            My alternative is a Michelin 23 which is 25.5mm which would be 1.1mm smaller. So which tire would be a better match for the rim?

          2. I think you’ll find both are in the same ball park. It’s not an EXACT measurement, so pumping the tyres up a bit more is going to skew that.

  6. 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

  7. 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.

  8. 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 ?

  9. 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 ?

  10. 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 ?

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

  12. 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?

  13. Any chance you would test the Winspace Hyper X Wheel (65mm). I was wondering about the absorbed wattage difference between the 50 mm and the 65mm of the same brand. Thanks!

  14. On the bar graph/chart above, you do not mention the yaw angle. Is it zero? If so, would there be an even bigger difference between the faster wheels and the slower ones?

  15. ….I meant: would there be an even bigger difference between the faster wheels and the slower ones at a greater yaw angle?

    1. It’s not quite a straight forward yaw vs drag analysis number. It’s based on transient analysis so it’s the speed of angular movement (amongst other things). To kind of explain this in a sentence or two using yaw angle:

      If you went from 6 to 15 degrees of yaw the flow would probably remain attached to 12 and then detach. If you went the other way (15 to 6), you would find the flow would remain unattached until about 9 degrees.

      It’s to do with an established attachment vs establishing attachment.

  16. It would be very beneficial if you tested a box section/alloy rim, just to help the community visualize the jump to carbon aero rims

  17. Will using a 23mm tyre instead of a 25mm tyre on the Winspace 50mm rim – improve or degrade the benefit of the discontinuity that is present with the 25mm tyre ?