The Hour Record, Part 4: A Conversation With Robert Chung

Hi all @ Marginal Gains!

Firstly, thank you for reassuring me that it’s ok to speak in Douglas Adams Quotes!!!

As for my question: with the rule of 105% for tires/rims, and the benefits of wider tires, why do not more companies adapt for wider aero rims? Is the cost in the re-engineering to high or are there other reasons?

Thanks for sharing your knowledge and for the awesome audio quality, which makes it so much more enjoyable to listen compared to other podcasts!

Cheers, Max (Austria)

Awesome episode as always ! Loved Robert attitude, being so smart and humble at the same time, kudos !

Couple of questions regarding the 105% rule and CRR.

1) 105% rule :

– does it matter where the widest section of the rim is relative to the tire widest section ? Firecrest for example has its widest section close to spoke bed but pretty far from tire and is actually narrower than most tire at brake track… creating kind of peanut shape more than an airfoil shape… so should the 105% rule be at brake track or external part of the rim in case of a disc brake rim since brake track does not apply (even if it means a toroidal shape that is actually 120% widh of tire width somewhere in the middle and 105% at brake track) or should it be 105% somewhere on the rim but it does not matter where?

– Zipp 858 NSW is a different beast with the 18h rim (front rim brakes) being 24.4mm max width and the 24h rim (rear rim brakes & front and rear disc brakes) being 23.7mm max width… meaning all tires even 700×23 are going to be wider than the rim with the 17mm internal width. So what do the Zipp engineers know which allow them something that does not respect the 105% rule at all ?

2) CRR

– when doing aero testing I’m trying to be as precise as possible regarding all parameters but it’s almost impossible to know what’s the correct CRR is on the road I use for testing. Do you have any advice to calculate CRR properly ?

Thanks again, looking forward to the next episode(s).

Here’s a question I don’t know the answer to: do patches on a tube affect Crr? Do different patches have a differential effect?

Fortunately, I haven’t gotten enough flats to do a systematic comparison. I was thinking about testing a brand new tube and then putting unneeded patches on it but, before I do that, I was hoping you’d already done the test.

Well, thanks. That was much less traumatic than I feared — at least for me; apologies to those of your listeners who aren’t on the spectrum, but maybe they can use it as a sleep aid.