Newsgroups: rec.bicycles.tech
Michael Press said:Quoted message said:As I said, an unglued track tire on a clean rim responds the same
as the clincher. Or even a mylar torus resting on a clincher rim.
All this glue and rim shape between the edges where the tire rests,
is a smoke screen and has no effect on the problem.
Quoted message said:Does the mylar torus constrict as much as the bias ply tubular tire?
It wouldn't constrict at all. Constriction is what holds tires on
rims but has nothing to do with supporting loads. The point is the
tire features that seem to get in the way of understanding how tires
support rims are not present in a featureless mylar tube. The mylar
tube is merely a model for visualizing the effects.
I'm glad you brought that up because constriction an interesting
effect related to tire blow-off, considering that a bias ply casing
constricts onto the rim proportional to its inflation pressure. As I
mentioned, this can be calculated and would suggest that tires won't
blow off.
The light bulb just lit up. Blow-off is a condition caused by lateral
casing pull from the tire bead, a force that is not affected by
constriction. Therefore, a narrow tire no wider than the rim, lets
say close to 20mm or so, could not be blown off no matter how high its
inflation, also because the casing would burst befored than 300psi.
This explains why narrow racing clinchers can be inflated to such high
pressures while fat tires cannot. Typically tandem tires that blow
off are much fatter than racing tires because their lateral casiong
tension readily overloads the clinch.
From test of riding a 25mm tire at 200pis around town convinced me
that it is primarily heat that allows tires to disengage rather than
the pressure because pressure does not increase significantly from rim
(brake) heating. Tire bead material becomes soft and lubricious at
high temperatures and can creep right out of the clinch. This struck
me the other day when I saw an old Mephisto (aluminum) 'clincher' rim
that had no hooked bead. Such rims will not hold fat tires.
Eureka, or is that Yreka? No that's near the California/Oregon border:
http://maps.google.com/maps?oi=map&q=Yreka,+CA
http://www.yrekawesternrr.com/
http://www.craigsrailroadpages.com/yw/index.htm
Jobst Brandt