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raider91e 06-03-2011 12:30 AM

So I almost had a heart attack today...
I was driving home doing about 30-35mph or so. I turned a corner and I felt a really nasty bump and a weird grinding noise. Then I hear hissing. TPMS goes off, and whatdya rear right tire is losing pressure fast. I look to inspect the tire and theres a nice 1in gash in the sidewall, not to mention a healthy gash on the rim (18" ****!!!!) The rest of the story of pretty standard and uninteresting...I just proceeded to change the tire and called up the dealer.

But my question was...The past couple of days I was looking around my car doing spot checks. I went into the menu and looked at the TPMS to check my tire pressures. About two days ago by fronts were at 42 and my rears were at 38. Today my fronts were now at 40 and my rears at 36. I was just wondering if anyone else checked their tire pressures lately and saw a change like I did? I thought it was weird that the tires should lose pressure that quickly. 1 PSI/day? which means I'd have to inflate my tires every month? IMHO, that's a little unreasonable and I'd hate to think that my tires really were deflating at that rate.

White WK Swagga 06-03-2011 12:37 AM

Re: So I almost had a heart attack today...
Just 2 psi difference could be because of the outside temp. We had some days it was almost 90 but it was in the 60's-70's today on Long Island so that could possible be the reason.

raider91e 06-03-2011 12:49 AM

Re: So I almost had a heart attack today...
Yeah, I thought about that too. It was a little over 80deg here in NJ, and I was out driving all day. It was most likely due to these two to the dealer tomorrow morning to resolve the issue. Hopefully no one else has this problem.

2005JGC 06-03-2011 02:38 AM

Re: So I almost had a heart attack today...
putting 1 mile on a car you will see an increase in their pressure... I cannot remember the specific time but your not actually supposed to "fill a tire" or "top a tire off" if has been driven on in the last couple hours because it will (or could) be inaccurate. as mentioned tire pressures go up and down, your just fine!

dobiegillis 06-03-2011 06:10 AM

Re: So I almost had a heart attack today...
This is exactly why I bought the road hazard warranty. Im actually surprised I haven't damaged the wheels/tires yet given how horrible the roads are around here.

Technosavant 06-03-2011 09:30 AM

Re: So I almost had a heart attack today...
Temperature and pressure are intimately related. Higher temp, more pressure. To the tune of about 1psi per ten degrees Fahrenheit. So if you've had a wild temp swing, there you go.

Also, driving creates heat in the tire. Not only heat from the brakes (see the threads re: rotors), but from the deforming of the tire as it rotates. This is why they tell you check when cold- if you drove at all before checking pressures, something will be off.

CherokeeGuy 06-10-2011 03:28 AM

Re: So I almost had a heart attack today...
Ditto on the cold temperature pressure. Driving will significantly raise the temperature of the tire, as will air and road temps, which is directly proportional to pressure increase... PV=nRT.

Watch a NASCAR race and you'll see this in action every time they pit. On a hot day they'll only fill their tires to around 13psi (sometimes lower!), since they want grip, and they know their pressures will come up after a few laps.

The recommended psi on consumer tires is always based on cold temp for an average day. In the winter, be sure to top off you tires as temperatures the summer, you may need to bleed them a bit.

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