AJA 30: Debunking the Valve Stem Location Myth


We take our mission of making a big deal about the little things very seriously in this episode, where we talk about whether there's any actual basis for the superstition behind where you rotate the wheel to before inflating a tire. We then move to the admittedly more pragmatic questions of how much of a draft an aero rider provides to the riders behind them, the low-hanging gains for DH racing, and the problems with racing a 1X setup on the road. And that's not even remotely close to all (even though we could have talked about each of these questions for a full hour).


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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  • Sam

    Hi team,

    I ride a kneeling handcycle competing the in h5 class. You can see photos of my bike here https://www.instagram.com/iminabike/, but in a nut shell its a carbon tub that I kneel inside of with a long neck or stem attached to the fork, the bike has quiet a large side profile. I have two rear wheels that are at 6 degrees of camber. Currently I race and train on the same wheels, a set of 700c HED Jet 5s, but I do currently have access to a set of rear Corima disc wheels, these are 650c with 21inch tires, typically in a TT I average anywhere from 30 to 35 km/h.

    I have some important TTs coming up in the new year (which are likely to have cross winds) and I’m at a point where I’m prepared to direct some dollars toward gains and wheels seem to be the next piece of the puzzle (I kit and drive train fairly well sorted). I have always figured using disc rear wheels is the way to go in a TT as this is what the two wheeled bikes do, but recently I saw some photos of the top H5s in the world racing TTs with shallow or med section rear wheels and a more aero front wheel, this has challenged my thinking. So my question is where would my money be best directed? Into a more modern deep (either 65 or 80mm) front wheel that I can properly run rule of 105 on but risk handling issues, or a set of deep rear wheels and keep the jet 5 up front.


  • Bart

    Hey MG crew! Multiple chains to extend drivetrain life even further (than just waxing)? What’s the lowdown?

    For a long time, even before moving to hot melt wax, I used two or sometimes three chains in rotation with the idea that it will reduce drivetrain wear over the long term. My back-of-the-envelope theory was that as a chain ‘stretches’ it puts more pressure on the drivetrain teeth wearing them. If I change my chain every three months, I’m reducing drivetrain wear by ~33% because the next chain in the cycle isn’t hasn’t stretched yet so isn’t wearing the teeth further. Subsequent three-chain cycles will have the same effect: “x” amount drivetrain wear but multiplied by three-chain cycle = 3x longer drivetrain.

    Genius, wishful thinking, or …it depends?

    Bart (from Oztralia 😎)

  • Patrick Dicus

    As a racer on a tighter budget, I’ve found newer carbon wheels can often be quite expensive while carbon tubulars are often dirt cheap. For someone trying to marginal gain their tire setup on tubulars, what tires on the market would you recommend? What kinds of application methods are the best for rolling resistance (tape vs glue, etc). What are some other steps to get the most out of tubulars (thinking of adding sealant, and making tubular specific tire pressure calculations).

  • Alan Milway

    Hey guys
    I am a coach working with professional downhill mountain bike racers- I’ve listened to your podcast for years and thought the section on marginal gains for downhill was fascinating.
    I’ve looked in to a number areas
    To influence this and have taken your advice for road cycling to try and apply to my racers (we race World Cup and world championship events).
    The biggest issue is around CdA I think and ‘getting small’ where possible – especially with a wide handle bar of around 800mm and peaks on helmets.
    I’d love to discuss this further!
    Alan Milway

  • Jared


    My question is 2 parts and related to wheels. I have experienced rim-brake rub on a lot of different carbon wheels. I’m looking to buy a new set since my current wheels are rubbing my brakes even when they are one adjustment away from not functioning at all because of how far they are from the rim. I’ve owned 808s,404s, Easton EC90s, Giant SLR, and Token Ventous. Of all of those wheels, the 404 Tubular and the Giant SLR 30mm are the ones that I don’t recall rubbing. Will I be better off with a deep or shallow rim to eliminate brake rub, and how much of a role does the spoke bed (due to a stiff rim overpowering spokes and flexing away from the spokes) and actual spoke count/type play into the overall performance of the wheel?

    Second question- wide wheels are rough on rim brakes. One of the wheels I am looking at is 28mm wide and 46 deep. My question is regarding aerodynamics- if a 46mm rim is 28mm wide, wouldn’t it be aerodynamically worse than a 24mm wide 50mm deep rim running the same 23c or 25c tire? I see so many marketing claims that this new wider/shallower wheel is faster that a more narrow deeper wheel. I have a hard time believing that the wheel with a much larger surface area and lower length to width ratio.

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