Ask Josh Anything #005

Q&A Episode 5 –

In this 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), we try to stump Josh with questions like: Do stiff shoes matter? What’s the point of hookless rims? What benefits does steel have over carbon? What’s the weight vs aero tipping point? Are 23mm tires dead? Is graphene tire content anything but marketing hand-waving? Do integrated visors have real benefits over sunglasses? And what’s the right way to wear a cycling cap?

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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18 thoughts on “Ask Josh Anything #005

  1. I have seen while watching diamond league track and field events a racer who sports a half beard. He shaves it longitudinally. I am wondering about the potential aerodynamic benefits on a velodrome 4 rocking such facial hair.
    Is there anyone working at silca on which we could perform this type of experiment? Someone who really enjoys velodrome activities? We could see what gains are possible. Does it change the boundary layer of air through which the cyclist head is passing? Is there negative pressure behind the cyclist head with and without the special facial hair?
    If in fact there are notable gains with this type of beard, perhaps silca could launch a line a personal grooming products. I’ve heard this is a high-margin category. and you would be first to Market in the cycling industry. Any thoughts?

  2. Josh & Hottie

    I found last week’s issue on materials to be super interesting and informative ! I passed it to Jim Merz who used to be chief engineer at Specialized and he liked it too.

    thanks for sharing generously of your knowledge and insites !

  3. I continue to love your podcast. I must have been an engineer in a prior life.

    When running carbon clinchers (rim brake) with latex tubes… what is the inevitable failure with this combo. What is the rim temperature where we need to be concerned with failure? I assume you folks tested this in the zip days. The factors are expanding pressure from hot air within the tube, rim tape getting soft with heat, and the failure of latex itself.

    Are the failures generally in the rim tape? Air pressures that exceed system capacity? or latex just failing structurally from heat?

    What are some roadside signs of impending doom? As a 60kg rider in a more hilly region, my carbon rims have never felt more than warm to the touch. I have yet to check my pressures, but i run at 75psi cold, so i suspect i have plenty of headroom vs someone starting 120psi cold.

  4. Hey, thanks for answering both of my questions! Loved the materials show; as a mechanical engineer it’s always fascinated by industry war stories, especially so passionately and expertly told.

  5. On shoe stiffness…
    Stiffness near where the pedal is contacted can definitely be helpful, to distribute pressure across the foot. Platform pedals have always avoided this by having the platform itself be really wide, but in the case of clipless, the cleat and/or pedal where force is transferred can sometimes be very narrow.
    However, it’s hard for me to visualize how stiff arch support from the heel through the ball is useful. “Hysteresis” doesn’t seem like an adequate explanation, because it’s not obvious to me that a significant amount of power transfer ever goes through the back half of the shoe. Pedaling form is a lot like running form, the drive force tends to be pushed out from the front of the foot. The back half of the shoe mostly seems to be along for the ride.
    Things would be different if the shoe was rigidly locked to the tibia rather than to the foot, or if pedals were forced to stay at a constant tilt through their revolution. In these cases, simply pushing your lower leg downward would transfer useful drive force into the shoe even if the foot was left to flop around, and the shoe’s sole would transfer that force out to the pedal. But this would be quite different from the pedaling form that humans actually use while riding bicycles, at least those of us who have two complete legs and healthy feet.

  6. As a mechanical engineer and avid cyclist I’m loving the podcast. I stream it to my brain whilst doing my day job. My question that I have been thinking about for ages is related to aero dynamic effect in strong winds. For me I’m 178cm, 83kg rider on a Cervelo S5 2019 (lovely bike). Now if I’m riding into a 30kph head wind of course I’ll get down low into the drops to reduce the drag and go a little bit faster. However I turn around to head back and now have a 30kph tailwind. Is it faster for me to still get into the drops or sit up and present more cross-sectional area (my back) to the tailwind for assistance? At what wind speed should I change this positioning?
    Thanks Mike

  7. Hey Marginal Gains podcast team!

    Long time listener (since the first podcast earlier this year anyway)

    First time “caller” , I have a question for the “ask Josh anything series”.

    I just bought some new Zipp 302 wheels love them. Its what my full time student budget could afford, great wheel for the price point. Love the wheels, they work great for my local race scene. I use latex tubes (of course they are from silica! love them too) with GP500 tires.

    My question is kinda two part;

    1) the Zipp 302 wheels states on the wheels and the Zipp website max tire pressure of 125PSI

    (taken from spec)

    Max Tire Pressure 125psi
    Max Tire Pressure 8.62bars
    Okay, those are the limits although they seem kinda low,no?

    2) Because I’m busy with school, studying and riding my bike when I can I don’t really have time or the patients to pull off the Chung Method and test my ideal tire pressure.

    Vittoria tires offer an online tire pressure calculator.

    Example: I enter my tire casing -corespun 320 tip, Version – clincher, total weight- 175, Road condition-Mix.

    Vittoria says “front tire pressure at 120psi/8.27 bar and rear at 125psi/8.62bar.

    Question 1,

    >How reliable is Vittoria’s online tire pressure calculator? For those of us not using the Chung method or have friends mastering in Mechanical engineering at MIT.

    Question 2,

    >What am I to do when Zipp says the max tire pressure is right at my “ideal” tire for top performance?

    Thanks for the podcast and the great learning opportunity!!

    Andrew Lerner

  8. Hello everyone, love this podcast and look forward to every episode. Question – I currently run Zipp 404s with max rim width of 25 mm and internal width of 16.5 mm (I run 25 mm GP 5000’s). I’m looking at a new aluminum wheel set with aero characteristics similar to Zipp 303 (A force AL33) with max width of 26.2mm and internal width of 19.6 mm. As these new rims are wider than the tire I run (yet only 32.5 mm deep), does that make them faster than the 404s? They’d also save 200 g… Thanks for the input!

  9. Hello – Thanks for very interesting podcast! I have two questions about tubular tires which are becoming increasingly rare and difficult to learn about::
    1. Why 28mm Vittoria Corsa G+ tubular tires have higher minimum pressure (85psi as labelled on the sidewall) than 28mm Corsa G+ clinchers (70psi)? Is it related to minimum pressure required to deform tubular tire carcass enough to press against inner surface of the rim?
    2. Looking at the cross-section of tubular rim (Bora 35 in my case) and contours of 25, 28 and 30 mm tubular tires, by superimposing their to-scale images using graphics software, I see that rim is optimized to match the circumference of 25 mm tubulars forming almost perfect contact with inner rim’s curvature. Larger tires, on other hand, form minimal contact on the edges on;y, if not deformed. Does it mean that 28 and 30mm tires are still safe to mount assuming that tires will deform under pressure to form larger contact area with rim’s inner surface?

  10. Thanks for answering my question! I wish to point out that my BMC isnt solely used for commuting and yes I have a secure cage to lock it in with a Kyptonite lock.

  11. Hi,
    What is better for short distance triathletes (sprint distance – 20k bike) – an agressive position on the bike with a smaller frontal area and not really sustainable for longer rides comfortably, or a more relaxed position which will be a bit more comfortable for longer rides but has a larger frontal area?

  12. Hi!
    Here is a nerdy question for the “Ask Josh anything”-podcasts:
    I was thinking about the resistance from the freehub while coasting downhill. It seems the force in the chain from the freehub spinning would be larger when the chain is on the 11 tooth sprocket compared to a larger one. The torque is the same but the lever arm is not the same length with different sprockets, meaning less/more force. Does this mean that we can save a fraction of a watt while coasting by putting the chain on a larger sprocket, or is my brain missing something important? Sorry if the wording is not right, I am neither an engineer nor a person with english as my first language;) Thanks for an awesome podcast!

    1. The force on the chain is bigger in the small cogs, but the freewheeling losses don’t change; no energy is lost in the chain because it isn’t moving. And the losses within the freehub are the same, it’s putting the same torque on an unmoving cassette regardless of where the chain is.

      Some bikes from the first half of the 20th century actually implemented chainrests on the dropout that you could shift the chain onto. This was primarily to facilitate easy wheel removal with chainstay-mounted derailleurs and split wheel axles, but it had the interesting effect that you could shift the chain off the freewheel on descents and coast in silence if you wanted to. This probably reduced frictional losses, although it also meant that the freewheel would spin while coasting, so who knows if it actually saved anything.

  13. Not sure how to phrase this, because I may be mistaking your aims, but… say the goal is compliance + aero, why not start with a very comfy bike and then add non-structural aero bits? The answer is UCI rules, but the rules don’t allow 12lb bikes, either, and that’s not stopping anyone. It seems like requiring everything to be structural makes it harder because aero-shaping often makes tubes stiffer on an axis where we desire compliance. So the directionality of carbon’s strength is of great potential, but also complicating things. Thoughts?

  14. Great podcast. I always look forward to the next episode.

    Question: I currently have a wheel set that is 50mm deep and 27mm wide on a 2018 Specialized Venge. I am riding GP4000s on both front and back but am riding 25mm in the front and 28mm in the back. What, if any, difference in aerodynamic drag is the 28mm tire making due to the fact that the tire is slightly wider than the wheel? My thought was to optimize the front wheel for aerodynamics and the rear wheel for comfort.

    Thank you.

  15. Hey guys, terrific pod. Would love to hear Josh’s thoughts on Ineos using Lightweight hoops at the Tour de France (road stages). You have been excellent in explaining the science behind ‘aero Vs weight’. So I (we) understand the situations where the Lightweight wheels could start to have an advantage over their Shimano wheels, that would be heavier. Only does rim shape and aero still play a role in gradients over 7%? As it does not seem like Lightweight have developed their rim profiles like many other brands have. To that end, where do L/W sit in general terms of aerodynamics relative to their competition. Cheers.

  16. A quick ask josh anything question…for those of us who like to attach a mini pump to our frame (shock horror I know but sometimes it’s easier and comfier than in a bag or pocket) where’s best/least worst to attach the mount – on the bottle cage on the down tube or on the cage for the seat tube. If it helps to get my question chosen the pump in question is a silca tattico mini pump…

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