Bicycle Wheel Power Data 50km/h

Posted on 37 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.

37 thoughts on “Bicycle Wheel Power Data 50km/h

  1. I’m a fourth year MEng aerospace engineering student and haven’t heard of Dnitriev number before – can you explain what it is? You have referred to it a few times but I can’t find any information on it. How is it calculated, what factors affect it, what are its advantages? I want to include it in my thesis in aerodynamics as a comparison to other methods and metrics. Thanks!

    1. It is a ratio of local vector to global vector. Dinitriev is a “trade name”. It might be called something else depending on where in the world you are. Additionally, unsteady aerodynamics is rarely taught at undergrad level.

      1. Hi Hambini,

        Thanks for the explanation, and that makes sense why I haven’t seen it at uni. Do you have any good references / textbooks that explore it a bit more?

        1. Aerodynamics by Anderson has a section in it – I think

    2. It’s “Dimitriev” with “m” not “n”.

  2. What is that aliexpress 3 spoke wheel at the top? Can you feature that wheel?

    1. it’s a deerocatcher or something like that. it’s sold under various names

  3. Any chance you could review the ICAN Aero wheels? Road.cc seem to hate them, but forums seem to think they’re a hidden gem. Not sure who to trust!

  4. I would like to see some data on old school wheels, how much power savings for 28, 32 vs 36 spoked wheels? Thanks!

  5. so the tri spoke is more aerodynamic than 88mm rim?. or both tri spoke and disc vs pair of 88mm rim?

    1. Tri spoke and disc is the fastest.

  6. Reynolds wheels seems to perform quite well with more of a V profile rim. Is this because it is closer to an aerofoil shape?

    1. yep it is and they tend to be slightly narrower as well.

  7. Have you ever tested any Boyd wheels?

    1. afraid not.

  8. Have you looked at testing the Fast Forward Falcon two spoke front clincher? It would be interesting to compare the data to the 3 spoke wheels.

    1. They have not been tested I’m afraid.

  9. Why the 454 performs so poorly agaisnt the same class of wheels? It’s full 11W and 13W more power absorbed against Giant SLR 55 and LightBicycle WR56.

    1. Mainly because the sawtooth makes it worse.

      1. Thank you so much for all that you do! Have you seen LB’s new sawtooth rim which they claim has about 25% less drag then their traditional wheelset in the same depth. Bullocks?

  10. Reynolds wheels seem to be very good, what are your 2 cents on its very V sharp profile? Compared to something like the Swiss Side or their new VU shape for 2021? https://cdn.shopify.com/s/files/1/0299/3917/1373/products/2018_Aero_65_DB_4ea184f7-bf0b-4b7c-b358-12622898e4bc_1000x.png?v=1583880428

    Also, what do you think about this new trend of super wide rim profile? Like the new Aeolus RSL, with 23mm inner and 31 outer

    1. I think the super wide thing is a “flavour of the month”, it will go out of fashion a bit like the previous trend towards narrow axle cranksets and pressfit bottom brackets (general trend is to move to threaded). V shaped profiles verge towards aerofoil sections at the top of the wheel where it matters so they are effective. The Swissside wheels are well designed because they use a small hole and measure the width for leakage. Aerocoach which adopt a similar construction got it horribly wrong and consequently have very poor performance.

  11. Hi! Have you ever tested 4 spoke wheel? If not, based on your experience, what will be your guess on this a wheel with 4 vs 3 spoke?

    1. Generally a lower spoke count is better but there is also a structural trade off. For vibration issues, I’d always recommend an Odd number.

  12. Hi, very interesting!
    Quick remark for the budget oriented triathletes, what do you think performs best for the rear wheel on something like a 36-40kph effort?

    – a standard 50mm deep section wheel (bontrager aeolus, yoeleo c50, mavic cosmic pro, …)
    – or one of those home made disc wheels as made famous by GCN (https://youtu.be/qevfMwzGPmc)

    Does it make sense that I start DIY’ing? Or would you say, don’t bother with custom built contraptions?

    1. A disc wheel will always perform better but not necessarily the one from GCN. it might “Boom” too much. A cheap wheel from an online supplier would likely be fine.

  13. Hi Hambini,

    What are your thoughts on valve stems?

    There are some products marketed as reducing drag, such as this:
    https://www.shopforwatts.co.uk/products/anemoi-aero-valve-cover

    I’ve made my own and 3d printed them:
    https://imgur.com/a/8jaUkHt

    Would they likely help? Would they make things worse?

  14. I do enjoy reading your articoes and based on those aero test I’m 99% into buying Hyper wheels .
    One small thing: you mentioned Hunt wheels as one of the worse performers of the aero test, same Hunt who uses the EXACT rim profile and layout as Hyper on their Hunt Ud wheels set, so now the Hunt rim is good?..

    On the other hand there are some realworld tests of the Hyper wheels downhill and it seems that somehow, at 50kmh + they tend to be less fast than Bora for exampe (you can have a look at the thread on weightweenies), maybe due to the large spokes.
    What do you think?

    1. I believe the hunt wheels above were an earlier model year

  15. I’ve bought a Yoeleo ‘disc disc’. If I get an aliexpress trispoke front wheel, will I win my local 10 TT?

    1. probably.

  16. Also appreciate all the work and time you put in to give us another perspective! Like another person asked above, any chance to look at and consider the LB “x-flow” profile? It looks like it’s kinda different from zipp sawtooth that has variable depth, opting for variable width!? I guess I could imagine maybe a crosswind buffeting benefit, but is that even real?

    1. if one comes along, it will be tested.

  17. Thanks for all the work, super helpful and entertaining!
    The U-shaped rim profile is said to be more stable in crosswinds. But after seeing your aerodynamics masterclass video I’m hesitant on them because I’m guessing there’s a major aero penalty because of the steep alpa number.
    What’s your take on U-shaped rim profiles?

    1. It’s not a question of V versus U, it’s more an issue to do with alpha critical angles. I would take a look at the aerodynamics masterclass video to take a look.

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