kenf@tekigm.UUCP (Ken Ferschweiler) (11/08/84)
[When bug-killer lines are outlawed, only outlaws will have bug-killer lines] >Ah, but what happens when you come down a long, winding hill, using >considerable braking? Although I don't carry a thermometer around in >my cycling clothes, I've had rims too hot to touch (even when pumping >the brakes) after a hill. The real test of heat blowing tires comes on loaded tandems on hills; which is why most tandems carry a rear hub brake in addition to caliper brakes. (The hub brake is not for stopping the bike, but for slowing it down). There is some question, though, of whether hub brakes are necessary; while there have been cases of tires blowing off rims on braking tandems, these may be attributable to defective or worn tires. Rodriguez (forget his first name), who builds Rodriguez tandems, had some folks test brakes by *pedaling* a heavily loaded tandem down a 20% grade for a couple of miles with the brakes on. The rims got hot, but nowhere near hot enough to blow the tires. I've seen new Rodriguez tandems since then without hub brakes; the owners say they work fine, and they save the cost and weight of the extra brake. Specialized has tested their Turbo-S tires ( a very light, high-performance clincher) to pressures up to about 285 psi; in some cases, the rims have split before the tires have blown! In general, modern high-performance tires are more likely to go flat due to under-inflation than over-inflation. The casings can take extremely high pressures, but not the pinch that may occur when you hit a bump on a soft tire. Ken Ferschweiler ...tektronix!tekigm!kenf