I admittedly don't pay enough attention to the air pressure in my tires but noticed something today...

As I was exiting my car today I took a minute to read the placard on the driver's door. It says that the front tires should be at 37psi, however, my front tires have been at 32psi for quite some time. Is 5psi significant enough to impact handling or gas mileage?

Anyone know how low the air pressure must fall before the TPMS alerts to low pressure? My air pressure dropped to 29psi on an extremely cold evening in the foothills of California and the TPMS alerted that one of my tires was low. The next day, tire pressure fluctuated between 31-32psi and the low pressure warning remained on. I checked the tire pressure of all four tires to verify the TPMS reading and it was spot on. I stopped by a dealer to have them check it out and they said it was a faulty sensor and replaced it. They also set my tire pressure to 32psi all around and that's where it has been since.

 

Yes, 5 psi is enought to affect ahndling and mileage.

Not sure what the alert limit for TPMS on these cars is. On the 3G TL ('07 & '08), it's 28 psi, IIRC. BUT those cars are recommended closer to 32 - 35 psi.

 

If you keep the tire psi in the right range from now on you should be ok.

 

depending how warm it is outside mine will start off at about 32-34 and end up around 37-39 after a few minutes on the highway

 

Check the placard closely. I dont remember the exact specs off the top of my head, but I do know that the SH-AWD models call for a different tire pressure than the standard models. I believe the AWDs call for 32 and the standards call for 37. Double check that tho.
I was told by a service tech that the low pressure indicators go off at 29 psi. Havent verified that tho.

 

I think its 37 psi in the front for HPT and 32 in the back. Regular tires are 32 psi all around.

 

yep

 

This is normal - tire pressure changes with temperature.

The correct time to guage tire pressure is when they are cold; before you've driven the car. The recommended tire pressures are COLD pressure measurements.

 

^^ Interesting point. I always thought 32psi was the warm temp. My tires have started at 27 to 28psi from day one and run at 32psi warm. Guess I need to put in some air.

 

That should also give you better mileage. When running low, the contact patch is larger thus more friction.

 

As stated above... HPT or 19's are 37lbs COLD front and 32lbs rear. The TPMS system is setup to give you a warning when you lose 20% of the recommended pressure. In the HPT's case it is set to come on at 29lbs. When you upgrade from the factory 17's or 18's to the HPT's (19") or bigger you need to have the system programmed to recognize the new pressure. Otherwise your TPMS will be waiting for the fronts to be down to 25lbs or so before warning you which would be bad as you would then be down 12lbs or more.

I always check mine in the morning before driving. My tires are the Pilot Sport Plus A/S which have a max COLD of 50lbs.

I run 80% of that in the fronts, so 40lbs front for a 3lb difference and since the rears are a lower pressure I bump them by the 3lb to 35lbs. This has worked for me on all of my high performance vehicles, and I have never worn out the center patch etc. I have always experienced even tread wear doing it this way. I personally feel a little more connection with the road and the car responds in my opinion much better.

Technically if your pressures are low you should see a "slight" decrease in mpg's.

 

Thanks, makes sense. I was wondering why 29psi set off the warning and even after making it off the mountain it remained on as the pressure "normalized". It was odd that the warning came back on the next morning for the same tire at 32psi even though all 4 were set to the same psi. Any-who, the dealer promptly replaced the TPMS sensor and I reset the pressure up front Monday night after I read the placard.

 

I drove this morning for the first time with my tires inflated to a level where they are actually supposed to be. What a difference. Less rolling resistance but I also feel more of the bumps. I have been driving this car with 32psi warm. In cold temps, the pressure was as low as 27 lbs. What a nuckle head

 

^^^^^ Nice huh
I myself do not really feel all that much of a difference in bumps etc from the recommended 37lbs to the 40lbs that I keep in them. But then again I am used to running low profiles with 80% max Cold all the time.

 

So wait, i've got 35 profile tires, should they be at 44psi cold then? 80% of the 55 max on the tire?

 

Pete, it is a personal thing for me. I was given this advice by a Michelin rep when I was auto crossing. This was 10 years ago with one of my Vette's, and have been doing it ever since with all of my vehicles no matter what brand of tire I am running.. I personally like the ride compared to the lower psi's that car manufacturers recommend as I find them to "spongy" for my taste. I was told by him that the manufacturers do this on purpose because of the consumers mentality of a "smooth" ride instead of one that gives you more "feel" of the road.
I asked him what damage is done to the tire when the psi goes above the max cold rating when the tires are warmed up. He explained that the the tires are "designed" to handle the additional pressure that is caused when they are warmed up hence the "MAX COLD" designation.
He said that is why they recommend 80% of cold in order to take full advantage of the tires designed capabilities.

I am religious about maintaining proper "cold" pressures (checked once a week in the morning) and balancing at every rotation which I do at 5k miles because of the 2200-2500 miles I do each month.

Some might call that overkill, however I always seem to get max life out of my tires without any abnormal wear patterns.

Just like everything else here, it is up to the individual to find what he/she likes best in the handling characteristics of their vehicle. Personally I would never run anything less than recommended of course... ie HPT's are 37lbs front, even though there are those that will run them with 32lbs because of the "softer" ride.