Ask Josh Anything #004

Q&A Episode 4 -

We didn't set out to turn every other episode of the Marginal Gains Podcast into the "Try to Stump Josh" game show, but at least 2/3 of the hosts of the show are glad it worked out this way. In this episode, we ask Josh what he thinks of Zipp's new MTB rims, puzzle over why the GoPro is so non-aero (and how to mitigate that non-aero-ness), discuss aero cranks and why they aren't any bigger of a deal than they are, talk about why it's faster (sometimes) to ride the white divider line, wonder why ceramic bearings don't (usually) turn back into sand, detail the steps for figuring out CRR in the field, explain why heavier riders descend faster, and — believe it or not — more. Enjoy this new Q&A episode of the show that makes a big deal about the little things, and how those little things can be a big deal.

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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  • Wilson Tran

    Hi Josh,

    As a bike racing mechanical engineer, I’m absolutely loving listening to your insights on this podcast!

    While tire Crr on a set of rollers has been shown to be weight agnostic, in your testing, have you found that the “break point/impedance” in pressure changes (shifts left or right on the pressure axis of the graph) dependent on mass? Ie, would the break point pressure be different for a 75kg mass vs a 100kg mass?

  • Sam Clark

    Frame Aerodynamics VS comfort.

    For a long distance TT on rough chip; could it be more efficient to ride a steel frame vs, an Aero- Carbon frame if it allowed the rider to hold a more aggressive aero position due to increased comfort?

    The road surfaces here in NZ can be pretty bad.

  • Ron

    In the recent episode Josh mentioned how the flat wear on a tire was terrible for aerodynamics. However it seems to me that the rear tire is more prone to this type of wear and because it is shielded is it really an issue? Also typically the front tire wears more rounded and again does this wear have significant impact on aerodynamics.

    The other thing I was thinking about was frame design and high frequency vibrations as noted in regards to rider fatigue factor and also bike aspects of power transfer. We composites being so tuneable and new alloys and tubing manufacturing methods can bike now be tuned to minimize high frequency vibration transmission and maximize power transfer. Added to this what is the situation between say carbon fibre, steel and aluminum for the frame in this respect.

    Keep up the great info Podcast. It is the only one I listen to every episode.

  • Kar-Soon

    Loving the podcast – thank you from Australia!


    1. is the smaller vs heavier rider descending is a non-linear scaling issue? F = mass.acceleration (gravity). Mass is scaled to volume (to the power of 3), whereas aero drag (CdA) is scaled to area (to the power of 2). So larger riders have much more mass than frontal surface area.

    2. hysteresis. Clothing is everyday issue that responds differently depending on whether you are moving up or down the input variable. One often puts on an extra layer (jacket, gilet, arm warmers) when the temp is below a certain value, but then don’t bother taking it off until the temperature is slightly warmer than that value. Similarly for wet weather gear and the “heaviness” of rain. One puts on rain gear as the rain reaches a certain threshold, but don’t take it off again until the rain has eased off more. I guess the degree of hysteresis is our range of tolerance to temperature /wetness, plus laziness to add/remove layers.

    3. Josh – will you dig deeper into the marginal gains in Victor Campanaerts hour record? You said you loved the hour record as a topic.

    Thanks again, and keep up the fantastic work!

  • John

    When i say gear selection i mean aero vs light bike (lets pretend no uci limits to weight). Also heavy tubeless clinchers (corsa speed tubeless) vs lighter tubular with inferior Crr. Also, heavy aero wheels vs light climbers wheels.

    And talcum power for your tubes. Is it just for easier installation and removal, or are there some marginal

    Crr gains.

    Thanks, love the podcast, as it covers many of the topics i frequently think about.

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