jim Posted August 17, 2011 Share Posted August 17, 2011 I'm not great on physics, but understand the principle that air pressure increases as a result of an increase in temperature. I've got a set of split rims that have been leaking and am testing one that's hopefully been repaired to make sure that it's holding air, so I bought one of those digital pressure gauges to make sure I'm taking consistent readings rather than various different air machines at petrol stations. I expected there to be a little bit of a difference between a cold reading and a hot one, but I checked this morning before heading to work and the reading was 31.7psi...25 miles later when I got in to work I checked again and the reading was 35.9, which is a variation of about 14%. For my purposes it doesn't particularly matter as I will compare the cold readings to the cold or hot to hot to see if the pressure is dropping, but I was wondering if this level of change is normal? Does it matter if you inflate your tyres when hot or cold, eg if I inflate to 35 when they're cold then they'll be 40psi when hot, or is that a stupid question? Quote Link to comment Share on other sites More sharing options...
kill1308 Posted August 17, 2011 Share Posted August 17, 2011 As far as I'm aware you should always check your tyre pressures when cold Seeing higher pressures when they are warm is normal Quote Link to comment Share on other sites More sharing options...
bodilx6 Posted August 17, 2011 Share Posted August 17, 2011 You are on the right track. Temp variances make for quite a difference in pressure. Go to a trackday and see people adjusting tyre pressure constantly as its one of the most important part of getting the optimal grip and tyre wear. Depending on the cold temperature you start with, I would see it as most sensible to inflate to the wanted pressure when you have the tyre at the temperature mostly use it with. Then just make sure you check you the pressure @ roughly the same tyretemperature each time it doesn't have to be at the same temperature as you when you inflated it. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 17, 2011 Share Posted August 17, 2011 Sounds a perfectly normal pressure rise, particularly for damp air from the average garage forecourt compressor. Quote Link to comment Share on other sites More sharing options...
mattysupra Posted August 17, 2011 Share Posted August 17, 2011 nitrogen refill will help loads on keeping tyre pressures constant. MGT Racing in Nuneaton have a nitrogen refill machine that will vacuum the air out also. You also have the kwik Fit etc that are now using them. But im not sure i trust them to remove the oxygen out of the tyre first. Quote Link to comment Share on other sites More sharing options...
jim Posted August 18, 2011 Author Share Posted August 18, 2011 Cheers for the replies Hadn't really thought much about nitrogen but remember reading about it here, might look into that. Quote Link to comment Share on other sites More sharing options...
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