Ask Josh Anything #005

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?

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.

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.

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 !

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?