| Re: Rim brake heat and clincher blowoff, was Re: Potential goodnews for Mt. Washington access.
Frank Krygowski <frkrygow@mousepotato.com> writes:
>> When the rim heats it will expand in all directions. So the
>> rim will become larger in diameter (taller) and it will get
>> wider. This will cause the tire to stretch to fill the rim
>> and decrease its aspect ratio.
>
> Spoke tension will restrain the diameter increase. The width increase
> will be only a few thousandths of an inch.
Dang, I forgot about the (isothermal) spokes. So the thermal
expansion of the wire bead will tend to make the fit looser. That is,
for a 100degC rise the bead diameter increases about
(100degC)(1.5e-5/degC)(27inch) = 0.04inch.
Not insignificant, but not huge. Note that Kevlar has a negative CTE
(at least at room temperature, I don't know what it does at
100degC)---do Kevlar beaded tires blow-off less easily than wire
beaded tires during braking descents?
Joe
|