Ask Josh Anything #008

We're back with more proof that we're willing to ask Josh practically anything bike-related…and that he's willing to take practically any question seriously. In Ask Josh Anything #008, we talk about what gas you should fill your tires with, the challenge of planning for endurance ride air pressure loss, marginal gains and Kipchoge's sub-2-hr marathon, which pedals are most aero and whether aero pedals matter (they do!), whether aero adjustments could make a difference in downhill MTB races (they could!) and —as always — much more.

Got a question you’d like to ask? Text or leave a voicemail at the Marginal Gains Hotline: +1-317-343-4506 or just leave a comment in this post!

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  • Danny

    Hi legends,

    We hear a lot from various frame manufacturers about the aero gains to be made when buying their latest bike… But assuming the same position, same wheels/groupset/rider/clothing etc, what is the actual difference (in watts @ say 40kph or time on a 40k TT) between something like the latest Madone and a round tube steel/Ti bike? Given you guys have said the frame is generally not a huge part of the aero equation it’d be interesting to hear your thoughts!



  • Jim adams


    Firstly I need to say that I love the podcast. Having studied engineering then moved into a career in sales I have forgotten much of my maths and physics principles. I do enjoy relearning it and in a cycling context it is a perfect combination.

    As a track cyclist I was excited to see the new team GB bike made by Hope in England. It’s pretty radical in design and the assumption must be that there are marginal gains in that design. I am really interested to hear Josh’s thoughts on that bike. I guess he hasn’t had any opportunity to review data on it so I’m keen to see what his gut feeling is initially, perhaps with a follow up at a later date when he has more information. Why that design? What are the benefits? Are there any potential pitfalls?

    Thanks again for the great podcast. Keep up the good work.

    Jim Adams



  • Tom

    For Ask Josh Anything:

    The Hour Record episodes got me thinking about rim choice for the road and track.

    My first set of CF tubulars were purchased almost 10 years ago and were a “V” shape.

    They felt faster, they were lighter . . . and downright scary on some of the Santa Monica Mountain descents when the wind direction changed.

    A few generations of rims later the wheels are way less scary in cross winds and seem to be just as fast (But who knows for sure. I’m older, fatter and slower. More a tugboat than a cutter.)

    Do these improvements transfer onto the velodrome? Do the newer rim shapes offer similar benefits on the track? Are you doing yourself a disservice in mounting a 21 – 23mm tire on a rim that bulges to 28mm?

    And, while we’re talking about wheels and aerodynamics. How do spokes come into play? CX-Ray vs DT Aerolite vs those mega blades on the Ksyriums? Spoke count + aerodynamics? Are wheel MFGs testing in a wind tunnel with various spoke counts to optimize? I have to imagine that spoke count doesn’t really matter with the 0-degree yaw but what about in cross winds?

    Thanks for the killer show!

  • Phillip Mercer

    I have a follow up Keith Richards’ (not that one) question.

    Prior to Josh’s response that aero pedals and even shoe covers provide a gain, I had been of the opinion that the air was too turbulent with both the pedaling action and the air disturbance off the front wheel.

    Other variables I can think of is that when pedaling actions differ, it would effect the gains, for example some may point their toes towards the road when sprinting or riding out of the saddle. Is the aero gain manifest in making the pedal stroke slightly easier or is it the system as a whole in the Q factor?

    Loving the show.

    Marginally yours,

    Phil from Brisbane

  • David Ward

    Another question….

    I see riders like Julian Alaphilippe and Jens Voigt ride with quite an obvious “fish tail” style with their front wheel. Do riders like this need to use wheels (and tyres) that are optimised for a higher average YAW than other riders? I could see them riding into a higher YAW than other riders on the same course, at the same time.

    Thanks for the great show!

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