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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23 thoughts on “Ask Josh Anything #004

    1. Good call, somebody should tell them to market it as such!! I don’t use things like this, so no comments on functionality, but looks much better than the brick!
      Thanks Alex

  1. Points of contact. To me the most important points of contact are the shoes and pedals. Like your opinion on where that ranks in terms of marginal gains. I am using aero aero light pedals stack height 8 mm and right on top of crank no float and custom don Landon shoes with proper othodics that are made for those cleats.almost no loss of power.i see a lot of very good cyclists with old Audi shoes and bad pedals. I really believe that they are losing more then 20 watts of power with system versus a very efficient system

    1. Cycling cap. I tend to wear one in the winter to keep warm and in the summer to keep sweat out of my eyes. My question is – peak up or down?

      Kind Regards, Andy

      1. Andy,
        Just answered this in Q&A 5 which will go live next week and it was the most fun question of the show.. thanks a ton for asking!

  2. 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!

    1. Thanks Kar-Soon,
      We answered part of this in the Q&A 5 that we just recorded today and will be live next Tuesday, with more to come on the hour record in a few weeks!
      Thanks so much for such insightful questions!!

  3. 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.

  4. 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?

  5. Big fan of what you guys are doing!

    My question for Josh:
    We know that tire casing losses dominate until the breakpoint pressure, when then the impedance losses dominate. If we were to increase our tire pressure past the breakpoint pressure, can we theoretically reduce the impedance losses by employing a form of suspension – effectively lowering the combined rolling resistance? For example, by fitting a carbon seatpost like the Ergon CF3 and Redshift ShockStop stem.

    Many thanks,

    1. Thanks Alee,
      You are on it… the key is to develop small scale un-damped or minimally damped suspension that can essentially add to the compliance of the system without robbing it of energy. So the Lauf fork is a good example of a design that essentially reduces impedance losses similar to a much larger volume tire. The Ergon and Redshift are close, but both have some inherent damping that starts to complicate things as that begins to rob energy. There is also so much that we don’t understand here yet, but working on it!!

  6. Love the podcast folks – keep up the good work!

    re: the new Zipp 3Zero Moto rims
    Was the restrictive patent not applicable to Mello Boumeester as he had a very similar single wall carbon rim in the marketplace a full 3 years ahead of Zipp? Maybe he was behind the patent, although I figured likely not given he was a one-man show back then.

    1. So the challenge with manufacturing patents is that they are really hard to enforce.. it would take real money to prove that company B is violating your manufacturing patent behind closed doors. So if the violating entity was Zipp in this instance, one of the largest and most successful companies around, pretty much any attorney is going to take this case as the potential upside is quite large.. whereas if the company is a one man show or even a moderate regional player the story is quite different…as they likely don’t have the money to defend themselves and really what damages could the patent holder receive other than putting them out of business, which, might be fine for some people, but risks making the patent holder look like a jerk causing a situation where they win the lawsuit, but lose the PR battle.

      There are really only 2 types of patent disputes in our industry: big companies slugging it out and little guys going after big guys. This follows the flow of money and importance to the companies involved but also takes into account the PR risk that a bigger company faces if they go after a little guy. Remember the Specialized trademark letter to the Roubaix bike shop? This was technically just a cease and desist letter and it caused Specialized heartburn for months and had no possible upside. My guess is that the patent holder in this case faced a similar situation.

  7. Hi Josh (and the rest of you),
    When Specialized introduced specific aero clothing a few years ago, it came in an overwhelming amount of different sizes to to be as close as possible to any riders body and avoid aero losses (ripples?). If I remember correctly, you also mentioned a trial of a very specific fabric in a wind tunnel that was ruined because the shape was not good and fabric flapped and that ended up being less efficient than any correctly fitted kit.
    Now to my question : How hard is it to bend a given fabric, because, if it’s too tight to avoid ripples, the fabric could be under tension and require higher force to be bent and/or stretched when your legs go up and down (aka pedaling). If you take a bib short and pull on it to stretch it you need some force, so you must lose watts when pedaling. Is is so marginal that it’s never been an issue? (I don’t think there’s anything too marginal in your eyes) or is the elastic nature of the fabric give you back the energy you just spent? Is it as always a compromise between tight and flat fabric vs a supple and easy to stretch one?
    This is a topic that mixes aero and energy loss, so I am very curious to hear your comments about that !,
    keep up the good work!

    1. Frederic, awesome question and it will certainly make a future Q&A episode.. the short answer is that you need to eliminate all wrinkles while making the athlete as small as possible (compression) while at the same time not making it such that the fabric is placing undue forces on the pedaling action of the rider.. oh, and all the seams have to be in the right places and the fabric textures and directionality relative to the wind can be super important.. and most of the riders will have different positions.. so in a sense, this is a massively multi-variate question that is super hard to answer, but we’ll tackle it in a future Q&A!

      1. Great!, I can’t help but listen to your comments, looks like it’s a topic that hasn’t (yet) been hijacked by the marketing depts of the industry companies we love so much (at least not as much as lightweight aero and stiffness of the bike itself).
        (Not marginal) Cheers

    1. 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.

  8. Hi, I have a question for the next ask Josh anything pod. Josh mentioned about the obsession that continues with weight over aero. However I assume there reaches a point that weight “outweighs” aero especially when hills are involved. Is it a 20kg aero bike? A 15kg bike? 10kg? How do you determine which way to go? For my commute, I ride a BMC Timemachine TMR01 over 21km with approximately 200m climbing all up. How do you determine aero versus their relevant weight penalty?

  9. reading again the Road to Roubaix and the importance of tyre pressures and leakage rates. Do tyres just leak air or do they leak faster being used on the road compared to being a spare in the team car? I assume leakage rate is proportional to pressure… so does the dynamic pressure fluctuation due to rolling on the road lead to a faster rate?

  10. 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.

  11. Hi guys,

    Random question about chains and gears and reducing friction.
    Is there anything to be gained from polishing the drivetrain? (Perhaps with a tumbler and different media?) One of the ideas behind waxing chain protocols is to remove any metal shavings/etc, seems like polishing could also help (so long as it wasn’t “too smooth”) I believe the Premier (Tactical) optimized chain uses Isotropic Finishing. I hear plenty about waxing and some about coating drivetrain parts, but nothing about polishing.

    Keep up the good work!

  12. The question and discussion regarding the action camera got me thinking about accessories. My question to Josh relates to the best mounting location for the Silca Tattico mini-pump. Does Josh recommend to mount the pump behind the bottle on the down tube or seat tube from an aerodynamic point of view?

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