Date: Mon, 28 Apr 2003 21:42:50 GMT From: "charles stoyer" <interpexnopsamhlink.net> Subject: Re: Tyre /Tire pressure at different temperatures
I always assumed that "cold" meant ambient temperature; that is, tires not heated from running (or from sun). PV=nRT, where T is in absolute, where 0 is as cold as it gets. So for a tire, P/T is constant unless you add or remove air or change the size of the tire. Thus, P1/T1=P2/T2 or P2/P1=T2/T1. Absolute zero is roughly -460F or -273C So 68F is about 528R (R is "Rankine", which is an absolute temp scale with degrees the same size as F), so that a change in 10F which is also 10R would change the temperature ratio by about 1/53 or about 2%. So at sea level, a tire with 30 psi in it actually has about 45 psi because the atmospheric pressure is about 15 psi. a 2% increase is about 1 psi. For Celsius/Kelvin temps, 20C is 293 K. Charles. "Derek Wright" <nospam.drwrighnopsamlobal.net> wrote in message news:PzFBjCTkhOvp-pn2-dBSbHh6hZeNInopsamlhost... > Reading the manual for the Saab it states that the tyre pressure for > cold tyres is 32 psi (for my combination of tyres and wheels) > > The temperature of the cold tyre being 20C or 68 F, it also states > that the pressure of the tyre will change by 2psi (or 0.1 bar) for > each increase or decrease of 10F > > The question is - do you take this into account when checking the > pressure of the tyres in excessevily hot or cold temperatures. >
 |
 |
 |
 |
 |
