Ask Josh Anything #005

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?

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!

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!

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.

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 https://www.zipp.com/wheels/302-carbon-clincher-disc-brake/ 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.

https://www.vittoria.com/us/tirepressure

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