Date: Thu, 01 May 2003 17:26:34 GMT From: "charles stoyer" <interpexnopsamhlink.net> Subject: Re: Tyre /Tire pressure at different temperatures
Also depends upon the ambient pressure of the air, which changes with elevation. This is quite noticable in Colorado and very noticeable for low pressure tires like ATV's. The pressure you measure is the difference between the tire pressure and ambient. The measured tire pressure is, of course, the "right" pressure, as far as following manufacturers recommendations. At sea level, ambient pressure is about 14.7 psi. So if your guage measures 30 psi your tire really has 44.7 psi in it, which is balanced out by the pressure of ambient air. At 11,000 feet, ambient is about 9.7 psi. So driving from sea level to 11,000 feet (the elevation of the Eisenhower Tunnel on I-70), your measured tire pressure would increase to 35 psi. An ATV tire, on the other hand, inflated to 3.6 psi at 6,300 feet where the ambient pressure is about 11.8 psi and then taken to 11,000 feet would now have a measured pressure of 5.7 psi which is well beyond where it sould be. I have experience with this and can verify that observation does indeed match the theory here. No one in Colorado changes tire pressure as they cross mountain ranges and change elevation by 5,000 feet or more, but ATV riders should pay close attention to this. Charles "MH" <nomailnopsamhere.no> wrote in message news:b8mmqs$u29$1nopsam1.tilbu1.nb.home.nl... No, the outside temp at the moment you inflate the tyre is not relevant, the only thing that counts is the pressure inside the tyre, indicated by the pressure gauge. However, if you are in a Swedish arctic winter and pressurise the tyres and then take that same car to Furness Creek, Death Valley in July, the pressure in the tyre will be higher there. ....