Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 (Tek) 9/26/83; site mako.UUCP Path: utzoo!linus!decvax!tektronix!orca!mako!jans From: jans@mako.UUCP (Jan Steinman) Newsgroups: net.bicycle Subject: Re: clincher tire pressure question Message-ID: <360@mako.UUCP> Date: Wed, 7-Nov-84 15:26:47 EST Article-I.D.: mako.360 Posted: Wed Nov 7 15:26:47 1984 Date-Received: Thu, 8-Nov-84 08:24:47 EST References: Reply-To: jans@mako.UUCP (Jan Steinman) Organization: Tektronix, Wilsonville OR Lines: 37 Summary: In article pws@faron.UUCP (Phillip W. Servita) writes, quotes: >In article dsn@umcp-cs.UUCP (Dana S. Nau) writes: >>> From: kfl@hoxna.UUCP (Kenton Lee) >>> >>> ...recommends that sport clinchers be pumped up to >>> 100-115 psi. Most clinchers have recommended pressures of 90-95 >>> psi. Is there any danger associated with higher pressures? >> >> ...--you're likely to get flat tires that way. Several times when >> riding in hot weather I've gotten flat tires simply because >> the tires got so hot that the air pressure got too high. > >Not Quite. if anyone out there remembers his high school chemistry, >the pressure difference caused by a change in temperature as extreme >as 30 degrees F to 100 degrees F is pretty trivial once converted >to the Kelvin scale. (it produces about a 12 percent increase in tire >pressure) so if your clinchers are pumped to 100psi at 30 deg F, >100 degrees will only increase the pressure to 112psi. FAR below the >safety factor of any reasonable clincher out on the market. > 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. We're no talking Mt. Evans, either. A steep drop of 400 feet is enough to almost make the rims sizzle, depending on rider's weight and riding (braking) style. Flippant remarks about "high school chemistry" aside, I have seen tires blow during and after hard or long braking descents. Most tires have a large safety margin, but use good sense, especially if you have hills like Upper Bucks County, PA! -- :::::: Jan Steinman Box 1000, MS 61-161 (w)503/685-2843 :::::: :::::: tektronix!tekecs!jans Wilsonville, OR 97070 (h)503/657-7703 ::::::