Cycling Forums - View Single Post - Potential good news for Mt. Washington access.

01-09-2005, 09:05 PM

jobst.brandt@stanfordalumni.org wrote:

> Benjamin Lewis writes:
>
>
[FK wrote:]
>>>>When you do this, please compare with a static pressure test of the
>>>>same tire and rim at room temperature.
>
>
>>>What do you mean by this. Inflation pressure is inflation pressure
>>>whether the wheel is rotating or not.
>
>
>>Are you saying that tire blow off depends only on pressure and not
>>on temperature? The test Frank proposes could confirm this.
>
>
> As I mentioned, rims reach their peak temperatures quickly on steep
> descents and we don't have problems because these are transients. Rim
> temperatures drop rapidly as soon as the brake is released if the road
> is fairly straight and allows cooling speeds. Treacherous roads are
> steep ones that require nearly continuous braking.
>
> The problem with a static test is that I believe wheel rotation may
> have an influence on how predictably the tire releases, there being
> constant motion between rim and tire. This is evident from the wear
> marks in the rim and the presence of a chafing strip on the tire bead
> at that interface.

This is a continuation of a somewhat spirited discussion that took place
about a month ago on r.b.tech. IIRC, at that time, several people
pointed out that room temperature, stationary tires can withstand very
high (over 160 psi) pressures without blowoff, and that therefore
blowoffs must be caused by something other than _just_ the pressure
increase from the heat of braking. I was certainly one who felt that way.

Others (I'll let Jobst say who) seemed to be claiming that the only
relevant factor was the pressure increase.

Thus, after Jobst determines pressure at blowout during hard braking,
I'd like to see the same rim subjected to a room temperature static test
at the same pressure. We'll then know if _only_ pressure causes those
blowouts. It's an opportunity to learn.

--
--
--------------------+
Frank Krygowski [To reply, remove rodent and vegetable dot com,
replace with cc.ysu dot edu]

01-09-2005, 09:05 PM	#92 (permalink)
Frank Krygowski Guest Posts: n/a	Re: Rim brake heat and clincher blowoff, was Re: Potential good newsfor Mt. Washington access. jobst.brandt@stanfordalumni.org wrote: > Benjamin Lewis writes: > > [FK wrote:] >>>>When you do this, please compare with a static pressure test of the >>>>same tire and rim at room temperature. > > >>>What do you mean by this. Inflation pressure is inflation pressure >>>whether the wheel is rotating or not. > > >>Are you saying that tire blow off depends only on pressure and not >>on temperature? The test Frank proposes could confirm this. > > > As I mentioned, rims reach their peak temperatures quickly on steep > descents and we don't have problems because these are transients. Rim > temperatures drop rapidly as soon as the brake is released if the road > is fairly straight and allows cooling speeds. Treacherous roads are > steep ones that require nearly continuous braking. > > The problem with a static test is that I believe wheel rotation may > have an influence on how predictably the tire releases, there being > constant motion between rim and tire. This is evident from the wear > marks in the rim and the presence of a chafing strip on the tire bead > at that interface. This is a continuation of a somewhat spirited discussion that took place about a month ago on r.b.tech. IIRC, at that time, several people pointed out that room temperature, stationary tires can withstand very high (over 160 psi) pressures without blowoff, and that therefore blowoffs must be caused by something other than _just_ the pressure increase from the heat of braking. I was certainly one who felt that way. Others (I'll let Jobst say who) seemed to be claiming that the only relevant factor was the pressure increase. Thus, after Jobst determines pressure at blowout during hard braking, I'd like to see the same rim subjected to a room temperature static test at the same pressure. We'll then know if _only_ pressure causes those blowouts. It's an opportunity to learn. -- -- --------------------+ Frank Krygowski [To reply, remove rodent and vegetable dot com, replace with cc.ysu dot edu]