Ask Josh Anything #17

No matter what topic — modeling, bifurcation, the smell of lubrication, chain innovation or even power loss due to new tire nubbies, tube width decisions, or even PFAS chemicals — the Marginal Gains crew can count on insightful questions from our listeners. We put all of these subjects to Josh in this latest "Ask Josh Anything" episode of Marginal Gains.

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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  • Vant Lammers

    Hey guys, love the podcast. I have a couple questions about tires.

    1. When selecting a tire for the fastest setup, I’m considering rolling resistance and aerodynamics. Rolling resistance is relatively easy to look up, but the aerodynamics of a tire is a little tougher to determine. I’m going by the rule of 105 and selecting a tire that will measure about about 95% the width of the rim when pumped up to my ideal pressure (which I of course know thanks to the Silca pro tire pressure calculator). Other than the rule of 105, I’m wondering if Josh has any other insights into how to pick a sufficiently aero tire.

    2. Secondly, when abiding by the rule of 105, I find that mounting a smaller tire on a wider rim can be extremely difficult to do. For me it’s generally a 700×23 tire on a 26mm external width rim. Do you have any tips or tricks on how to make that tire mounting (and unmounting) process a little bit easier.

    Thanks so much for taking my question.

  • nate abbott

    Hey guys-

    A waxing question: I live in the desert, Joshua Tree, CA, and wonder if you have tips for chain lube in my extremely hot, dry, and dusty neck of the woods. Often from May-September it will be 95-105 degrees when I finish my ride. I will usually ride early in the morning and try to get up higher in elevation, but coming back down to the house you can feel the heat. And if I ride in the evening my bike has been in a garage that probably hovers around 100 degrees all day. With all the sand and dust, a wet lube seems a bad choice, but is the wax just melting off my chain leaving it unprotected?

    Thanks! -Nate.

  • Gregor C

    Hello Marginal Gainers,

    on a longer trainer ride a watched a little documentary on the Pikes Peak International Hill Climb and the open and exhibition class competitors. The cars that get built for that race push the boundaries of technology by using every trick in the book. They use skirts, fairings and wings to manage airflow and downforce, short wheelbases to navigate the turns, oxygen for the driver, electric motors for better performance at altitude, etc.

    The days after when riding I thought about the concept of an open class hour record and what crazy ideas you could implement with no to minimum rules. We are talking mayor gains like pulling a near vacuum or at least a significant negativ pressure on the velodrome and riding with an oxygen tank, positions even faster than the superman (recumbent?), fairings on bike or rider …

    I would love to hear your of the cuff ideas for such an endeavour and how much further you could go over the UCI Hour Record.

    Love the show and all the best from Austria

  • Robert J Pickels

    Hello Marginal Gainers!

    A partner and I will be tackling the Kokopelli Trail in the late spring. We’ll have 142 miles and 15,000 feet climbing of singletrack, double-track, paved, and unpaved roads to tackle as fast as we can. Unless we stumble across a not-so-marginal gain, we will not be challenging for the FKT.

    Of the approximately 14 hours we’re planning on, we think that we could (safely) use aero-bars for approximately 10% of the time.

    My question:

    Does the CdA gain that occurs while moving from a standard mountain bike position to a moderately aero position outweigh both the additional drag and weight of the aero-bars when they’re not being used?

    My hunch is that the “juice isn’t worth the squeeze”; I think that something like TOGS may help narrower our grip, drop our elbows, and realize more modest savings but without the drawbacks of the full aero set up.

    It’d be great to hear your take.



  • Marco Parigi


    Thanks for your great podcast. I do have a quick question: I’m thinking about purchasing the new Zipp 303 Firecrest, which has a 25mm internal rim width and a 30mm external one. Now, they recommend using at least a 28mm tyre with this set of wheels. Once you take into account the massive internal width, I really doubt the rule of 105 can ever be satisfied with an inflated 28mm tyre, even if inflated at 50psi. What’s the catch? Can it be that, with a hookless rim, things are now different, ie. the tyre-wheel system has changed vs a hooked rim, particularly the transition between the tyre and the rim? I’m asking particularly knowing your past at Zipp.


    Marco from Italy

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