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Discussion Starter #1
Okay, I've been negligent. I have had my Mustang for just over two months now and have kept an eye on the oil level, coolant level, etc. so I don't get any nasty surprises from a car that is still fairly new to me. What I have not checked, however, was the tire pressure. The place where I work was closed for a couple of weeks for the holidays and my Mustang did not move from it's covered parking spot at home very much during that time. Having returned to work this past Monday, I have noticed that my car was riding/driving a bit odd. Not badly, just a little differently than what I have gotten used to. I figured that since it was parked for a couple of weeks and the weather has been going from warm to cold and back again, one of the front tires might be a little low, so I checked them when I stopped to get gas, using the built-in gauge on the air compressor at the gas station. I have Dayton Daytona 245/45ZR17 tires all the way around (they were on the car when I bought it) and the sidewall says that the maximum pressure is 40psi, but to check the specs for the individual vehicle blah, blah, blah. The sticker inside my fuel door says to fill the tires to 30psi. As I suspected, the passenger side front tire was at about 25psi - about 5 pounds low. No problem, I aired it up to 30. The driver's side front tire was dead on 30 while the driver's side rear was at about 29, so I aired it to 30. The big surprise was the passenger side rear tire. It was aired to almost 50psi! After saying a few surprised expletives, I let the pressure out to 30psi. My question is, does anyone know of any valid reason why this one tire would be inflated so high, or is it just that the last person to air up the tires screwed up? I have heard of inflating rear tires on a rear wheel drive to five pounds or so more than the front, but never that big a difference and never just one tire.

I guess it is a good thing I have been trying to conserve tire rubber and not doing many burnouts. I can imagine that overinflated tire popping! I just hope that running it over pressure hasn't weakened the tire already and that it doesn't end up causing problems down the road.
 

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If air was added to it in extremely cold weather and it was aired to 40, I think it could make it providing your temp was warmer today than when it was inflated. BTW, I keep mine at 40 so I get a touch better gas milage.
 

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Tire pressures can vary +/- 2 psi for every 10* ambient air temp. Obviously, cooler means lower pressure, warmer means higher pressure.
 

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Discussion Starter #4
I appreciate the responses. I knew that the temp could change tire pressure, which is why I thought a tire might be a little low to start with now that cool weather has set in. I never thought about it having possibly been colder when that one tire was filled, causing it to be overinflated when I checked it, but now that I think about it, I guess it is possible - especially if it were slightly overinflated to start with. What I do know is, my Mustang rides/drives like a different car since I aired up the one tire and let pressure off the other. Of course, that might also have a little bit to do with the fact that when I checked the tires and filled up with gas, I put a can of Sea Foam in the tank. It's hard to believe that I've had it long enough that it's just about time for the first oil change since I got it. Time flies when you're driving a 'Stang!
 

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one day i did a experiment to see, after running the car had had all tires set to 30psi. after the car cooled down about 2 hours lateri came out and checked it and the rears were at like 25, and the fronts at like 27.

remember the old highschool science class, gases expand during heat, and compress during cold. so hot makes psi up cold brings it back down
 

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Two mistakes many people make. Always check tire pressure when the tires are cold and NEVER trust those tire pressure gauges at the gas station! :tongue

Get yourself a good tire pressure guage and keep it in the glove box. Most will say the dial type are best but I still use the old 'pencil' style. Get a name brand. :smoke:
 

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Discussion Starter #7
Tominator said:
Two mistakes many people make. Always check tire pressure when the tires are cold and NEVER trust those tire pressure gauges at the gas station! :tongue

Get yourself a good tire pressure guage and keep it in the glove box. Most will say the dial type are best but I still use the old 'pencil' style. Get a name brand. :smoke:
I had kind of wondered about the accuracy of the gas station gauges, myself. I was pretty sure about this one since it read all the other tires pretty close to thirty. In fact, I double checked all of them before I let any air out of the one. Still, good advice. I have always carried a 'pencil' style gauge in any vehicle I have driven. I had one in my Ranger (no way I was trusting a 'built-in' gauge with big, offroad rated tires), but have somehow misplaced it when I traded. Have actually been trying to decide between a dial type, another pencil type or a digital. I have my doubts about the digital ones (accuracy), but if they work well, it would be nice to see a digital readout of exact tire pressure. My problem is, any time I get into the auto parts store, I get distracted by other stuff and forget my gauge!
 
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