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How quickly dies your tires lose pressure? Mine usually doesn't (at least that's what I thought). The low pressure light came on yesterday mid afternoon, and someone filled all 4 tires for me. I told the shop it's 44/46, but an hour later, all 4 tires were between 38 and 41. Several hours later, someone checked it and it lost pressure but I don't know how much. Since all the gas stations nearby either didn't have a air pump or was out of order, I went to another shop and the guy added to all 4 tires, but he didn't have a guage in him so it was just a guess. Got home an hour later and they were 42/44. This morning (7 hours later), they're 39/42.

Is this normal? I don't think there's a chance all 4 tires got a nail them.
 

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Tire pressure changes with heat. Tires get hotter or cooler depending an a few things such as where they sit and how much they are driven - cuz driving on them heats them up. Exactly how you drive on them also contributes to which ones get hotter faster than the others too. The best time to check your pressures is when they are the coolest and still for more than several hours and unmolested by driving on them. Only then can you get an accurate reading to compare against anything.

The recommended pressures should be take at that point and re-checked under the same conditions to compare on any losses. Sitting in garage or shade compared to the sun can change the pressures by a few psi, so can just a short drive (2-3 miles) in 80+ temperatures. Sometimes just the left side of the car in the sun and the right in the shade can result in pressures being a few psi different. So you see that your observations can vary quite a bit.

When you ask how quickly does your tire lose pressure, that question is rather vague. I suppose you mean when it's just sitting around, but IF there's a leak from something - THAT something whether it's a nail or a knife, is in the sidewall or the tread, is straight in or at an angle, has a BIG difference on the resulting loss in pressure. So I (nor anyone) can really answer your question. Combined with NOT knowing when or where or how you are checking your pressures also has enough of a difference to account for what you've said too.
 
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