UNC1334

Hey guys,

First off, I am aware that cold weather will decrease your tire pressure, but what is throwing me off is how quickly my rear tires seems to be losing pressure?

I park outside overnight, and it gets down to about 25 degrees F here at night. My front tires I run at about 38-40 PSI, and I JUST filled the rears up on Saturday to the same. I start my car this morning and both my rear tires are sitting at 30 PSI. This has happened ever since the dealer took my my wheels to refinish the rims about a month ago. Is there something they could have done that would be causing this? The can't think of a reason as to why the front tires are fine and the rear keep loosing pressure.

AndreaL

My front passenger and rear driver's tires do the same thing after being parked overnight. After driving for a few miles the tire pressure always goes up to normal again and the light goes off. It's always the same two tires, so I'm thinking it's the sensor. It's weird that the other two tires wouldn't be affected. I'm sending it in for servicing next week and will definitely ask them to check on it. I'll post any updates if I get some useful info.

Swacer

Couple questions first. WHEN are you measuring the air? Are you measuring it when your tires are cold and the car hasn't moved? Or after you have driven for some time, and got air at a local gas station?

If you drove and the tires are hot, and then inflated to 40psi, then parked the car, your tires will begin to cool. The tires will cool from 40psi down to approximately 34-35psi (assuming temperature losses here) at 75degrees, and then going down to 30psi in 25 degrees. That makes sense.

Now, if you are putting air into your cold tire from an air compressor (air compressor air will be warm) up to 38-40psi, when you go to bed, you can go from 38psi at 75 degrees (compressor air assuming equal mixing), down to approximately 35psi in 25 degrees and still be normal.

So it depends on when you're measuring. if you are cold measuring and you're down to 30psi (Lost 10psi over night), I would start assume you have one of the following:

1. A leak - perhaps you ran over something.
2. Perhaps the service guy did not properly apply seal between the wheel and tire (why did they refinish your wheel? Did they dismount it?)
3. Or he sealed it correctly and broke the TPM and its seeping air.

Keep in mind, the tire pressure it recommends is at 75 degrees ambient temperature.

UNC1334

Ah, I don't know why I didn't catch this. I have been inflating them while they are hot.

So should I inflate them while they are hot to say 45 PSI, and then they will cool to 40 and maintain (given they will drop to 35 overnight) but warm back up when I start driving again.

Swacer

Not quite. If you are filling them to 40psi when hot I would just keep doing what you're doing. Just don't be worried if you're at 32psi in the morning when it's freezing. Your best comparison to determine if there is an issue is to watch each morning. Is your tire pressure consistent at the same temps? If so, you're ok. If it's still dropping from one day to the next, then you might have an issue.

However, I keep reading over and over that your fronts maintain pressure. Are they dropping similar amounts of air overnight? If not. I really think you have a sealing issue

toyotatom

Rule of thumb is approx. 1 psi drop for every 10 degree drop in temperature. To see an 8 to 10 psi drop would take a temp swing of 80 to 100 degrees, are you seeing that kind of temp swing during a typical day. If not then you may have a small leak or something.