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Question came to mind because of some colder than usual weather we've had here these past couple of weeks, (-12°F at one point), and my wife's new fangled car with all it's sensors in its infinite wisdom told me the psi was low in all the tires.

Now, 1 or 2 psi is of course ignorable, but in this case we're talking over 5+ psi. Of course, as time went on the tires warmed up, Boyle's Law kicked in and the psi warnings cut off. But that's the dangerous part: Had someone inflated their tires at that temperature, taking them for a spin around the block, as the air heated to operating temperature, the tire pressure would increase and they risk a blowout, is that a correct assumption?

So, I'm posting this in case anyone has a similar question: Perhaps a person should take a spin around the block before inflating their tires, to warm them up first? And maybe refrain from tire inflation in the middle of July, until it cools down some? That would probably someone money at the air pump I'd imagine, if nothing else.

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up vote 2 down vote accepted

The general guideline used to be to check the tire pressure every 30 days. The theory I assume is that normally you wouldn't see drastic ambient temperature swings in a thirty day period. A couple of ballpark calculations show a theoretical drop of almost 5psi with a 35 degree temperature drop. I say theoretical because this doesn't take into account any small leaks. Manufacturers usually specify checking the tire pressures cold, meaning ambient temperature whether that is -5 degrees F or 95 degrees F. I your TPS is faulting on a cold start-up the tires are underinflated. If the fault clears after driving several miles they are still underinflated as the specified psi is for cold tires. As to your last point, yes you would want to let the tires cool down if you were checking pressure on tires that were hot from a long drive. After a 30 minute drive at highway speeds tire temperature can increase by as much as 50 degrees with a corresponding pressure increase.

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It should also be noted that under-inflated tires create a lot of frictional heat. This has the effect of destroying the tire over time. A few years ago, Ford Explorers were rolling over due to under-inflated tires. All this ads up to, like mikes said, you should be checking your tire pressure every 30 days at ambient temperature. The key is to ensure the tire is at ambient temp. –  Paulster2 Jan 18 at 23:52
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Also, keep in mind that tires can grab a lot of heat from the Sun. Best to check them on a cold day before the Sun is beating down on them. The owner's manual specified tire pressures are almost always well under the maximum that the tires can handle (snow tires are an exception, they tend to have pretty low max pressures), so when they go over by a few pounds when warm you're typically just fine. –  Brian Knoblauch Jan 19 at 18:48
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as suggested check at ambient temp. Do not rely on gauges at your local servo.A decent gauge showing both metric and imperial pressures is under $30 and a good investment

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