Contact Points and Marginal Gains

While we have just 5 contact points with the bike, each of those contact points are made of whole systems of contact points. And your tires are the ONLY contact points between the bicycle and the earth. Think about it: all the forces, traction, braking, cornering, all have to be transferred through tiny patches of rubber, dynamically moving on the surface of the earth. Clearly, contact points aren’t as obvious as they seem, which makes them a perfect topic for...Marginal Gains!

Got a question you’d like to ask Josh? 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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  • Romney Phillips

    Regarding the 23s I thought aero was best when your tyre width matches the rim width? On my TT bike I have HED S2 wheels and a 23mm GP4000 seems to be the right match for the rim. Would a bulging 25 be worse?

  • Nick

    Interested to hear what Josh thinks about why aero cranksets have not taken off yet, some 11 years after Zipp did the vumachrono?

    Also are you going to make aerobar pads out of the high efficiency foam?

  • Romney Phillips


    Only recently discovered your podcast and am really enjoying it.

    A question for you that is not really a marginal gain but I haven’t been able to resolve:

    Is there an advantage to being heavier when going downhill?

    Everyone says heavier is better and faster but with gravity’s acceleration being constant doesn’t it all come down to aero?

    In a vacuum objects accelerate at the same rate ith only wind resistance affecting the speed.


  • Robert Chung

    Nice, as always.

    Speaking of converting from Crr to mass, I did a little translation of Crr difference to mass difference (for two relatively low Crr tires: the Conti 4000S and Conti 5000) at different slopes:

    Re: the Velonews 1x vs. 2x drivetrain efficiency piece, the losses are in the chain, not the rings or cogs per se — the problem is that the chain has to 1) wrap around the cog and ring, and 2) chain speed is determined entirely by the ring size and the rider’s cadence — the gear ratio and cog don’t affect chain speed. Since power transmitted along the chain is the product of chain speed and chain tension, smaller rings (at the same cadence) mean slower chain speed so at the same power the chain tension must be higher. So when you have high tension and the chain has to wrap around a small cog, you’re doubly screwed (I believe that’s the technical term). You can see this in the super small rings used by MTBs: even at the same gear ratio, their losses are higher since chain tension is so much higher and the chain articulates around tiny cogs.

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