inflation

[21Rouge]

I know GM says 32 psi per tire. But a couple of pounds more per tire is good for gas mileage and still safe. The problem I am having is getting an accurate 34 psi per tire. For example today first thing in the morning, before leaving to work, one tire was 32.5 psi. I went to work and parked. Came out at lunch, very sunny all morning and warm; checked the same tire and the reading was 36 with my digital tire gauge . Can the ambient temp make such a huge difference for a car at rest? Any suggestions to get the proper 34?

[RIT]

Yes, there is a 1 PSI per 10 degrees change in temperature. And parking it the sun can really heat up a tire.

[GMJAP]

If you factor in 1psi change per 10 deg F, a 2 psi change from early AM to afternoon in the sun is reasonable, coupled with a 2 degree accuracy (very likely) on the gauge could give you the 4 psi deviation in your reading. So your two readings aren't implausibly different.Everything you ever wanted to know about tire pressure:http://www.tirerack.com/tires/...h.jspAlso, most gauges are rather inaccurate. The AccuGauge H series has been recommended by the Car Talk guys. I've got one and it's great. (11" straight, 100psi so can check the spare too) Kinda bulky, though.Good price on it here:http://www.getagauge.com/DialTireGauges.cfmEdit From one of the Tire Rack articles, regarding the effect of the heat from sitting in sunlight:"First, we mounted two tires on wheels. We let them sit overnight to equalize and stabilize their temperatures and pressures. The following morning we set them both to 35 psi. One tire and wheel was placed in the shade while the other was placed directly in the sun. We then monitored the ambient temperatures, tire temperatures and tire pressures through the day. As the day''s temperatures went from 67° to 85° Fahrenheit, the tire that was kept in the shade went from our starting pressure of 35 psi to a high of 36.5 psi. The tire that was placed in the sun and subject to the increase in ambient temperature plus the sun''s radiant heat went from our starting pressure of 35 psi to a high of 40 psi."

[Jaycie685]

So in other words, when would be the best time of the day to check tire pressure to make sure it's at the correct 32 psi reading?When it's sunny and after driving around for a while?

[GMJAP]

Quote, originally posted by Jaycie685 »So in other words, when would be the best time of the day to check tire pressure to make sure it's at the correct 32 psi reading?When it's sunny and after driving around for a while?Actually, it would be the opposite. In fact, you should never set your tire pressure just after you've been driving.From the general "Air Pressure" article on the TireRack site above:"It's important to remember that your vehicle''s recommended tire pressure is its "cold" tire inflation pressure. It should be checked in the morning before you drive more than a few miles, or rising ambient temperatures or sun's radiant heat affects it.And by the way, if you live in the North and park in an attached or heated garage you will "lose" pressure when you leave its warmth and venture into the real world outside during winter. Add 1 psi "cold" pressure tire pressure to compensate for each 10° Fahrenheit temperature difference between the temperature in the garage and outside."

[ragingfish]

I still don't see the reason for setting your PSI above manufacturer's recommended pressure?