Tire Pressure sensor accuracy
Le Mans Master
Joined: Mar 2005
Posts: 6,262
Likes: 2
From: 39.0N 105.1W
There've been a couple of reports of this. The TPMS sensors are single-ported; they are absolute pressure sensors. Most gauges are relative pressure sensors - that is, they measure pressure relative to the ambient. As atmospheric pressure decreases with altitude (around 1 PSI per 1800 feet, as I recall) it makes sense that you'd read around 2 PSI lower if you moved from, say, 1000 feet in VA to, 4000 feet in C0.
Its been claimed that the BCM is supposed to compensate for this, by reading local atmospheric pressure via the MAP (Manifold Absolute Pressure) sensor before startup, but that feature doesn't seem to work.
Its been claimed that the BCM is supposed to compensate for this, by reading local atmospheric pressure via the MAP (Manifold Absolute Pressure) sensor before startup, but that feature doesn't seem to work.
Le Mans Master
Joined: Dec 2004
Posts: 5,492
Likes: 808
From: West coast CA
The 44 PSI maximum is cold pressure, there's plenty of room there for normal increases due to warming. My tires stabilize at about 25-30 degrees F above ambient temp with normal driving, usually a 2 PSI pressure increase.
I normally run 36 PSI in front, adjusted to 10 degrees F above the normal seasonal low (75 for summer around here) and have only had the 42 PSI high pressure alert come on once - that being in 100 degree heat.
Still, the high pressure warning is sort of annoying, as (1) its only valid for the stock GY tires (my PS2s are rated 51 PSI max) and (2) it doesn't take heat into account. Anyone know how to change that?
I normally run 36 PSI in front, adjusted to 10 degrees F above the normal seasonal low (75 for summer around here) and have only had the 42 PSI high pressure alert come on once - that being in 100 degree heat.
Still, the high pressure warning is sort of annoying, as (1) its only valid for the stock GY tires (my PS2s are rated 51 PSI max) and (2) it doesn't take heat into account. Anyone know how to change that?
I haven't tried the PS2s. You like what they're doing at 42psi?
Drifting
Joined: Jun 2005
Posts: 1,837
Likes: 4
This produces fairly even temps across the tread, and so far wear is pretty even - a few percent more on the inside. I do like the tires - not the most economical choice, but a lot of fun.
I'm somewhat compulsive about tire pressure, these are my normal settings but I'll drop a couple of PSI if I'm planning some spirited driving on a warm day or will add some if I ever find an autocross on a day I have free.
I had the about same experience with the GY Supercars, and after some testing I ended up back at 30 PSI. I guess that it makes sense that they'd want less air, as the sidewalls alone are able to support the car.
Race Director
Joined: Sep 2000
Posts: 11,142
Likes: 1,913
From: Missouri City, TX
It has also been my experience that the TPMS sensors read 2 psi low (which of course is the safe approach to avoid under inflated tires). That experience is consistant across the two vettes and the one CTS I currently own.
Team Owner
Joined: Sep 2000
Posts: 25,015
Likes: 2,709
From: Far NW 'burbs of Chicago
St. Jude Donor '13
...
I continue to be amazed at the low pressures (30 psi cold) that Chevrolet recommends for the Corvette tires. Porsche recommends 39 psi in rear of my 911 for partial load and 44 for full load. Front is 33 for partial and 36 for full load. I have owned three previous e46 M3s, and the recommended pressures were 33 front and 38 rear for partial load, and 44 rear and 38 front for full load. The Corvette pressures are as low as I have ever seen for a performance car for street use.
I know you are going to say you will wear the tires out in the center with those pressures, but not so. My tires wear evenly across the tread with those pressures. In fact, too little air will cause ultra wide, low profile tires to wear in the middle because of the tire expanding out in the middle on acceleration. A tire with higher pressure will tend to maintain its shape better under acceleration and minimize that effect. Don't believe me? Check the tires on your cars. Most of you run 30 psi front and rear. I bet your rears tend to wear in the middle but not the fronts. Wonder why? It is because the rears tend to expand out in the middle under acceleration and the fronts of course do not. If it was not for that, don't you think your fronts would wear out in the middle also?
I continue to be amazed at the low pressures (30 psi cold) that Chevrolet recommends for the Corvette tires. Porsche recommends 39 psi in rear of my 911 for partial load and 44 for full load. Front is 33 for partial and 36 for full load. I have owned three previous e46 M3s, and the recommended pressures were 33 front and 38 rear for partial load, and 44 rear and 38 front for full load. The Corvette pressures are as low as I have ever seen for a performance car for street use.
I know you are going to say you will wear the tires out in the center with those pressures, but not so. My tires wear evenly across the tread with those pressures. In fact, too little air will cause ultra wide, low profile tires to wear in the middle because of the tire expanding out in the middle on acceleration. A tire with higher pressure will tend to maintain its shape better under acceleration and minimize that effect. Don't believe me? Check the tires on your cars. Most of you run 30 psi front and rear. I bet your rears tend to wear in the middle but not the fronts. Wonder why? It is because the rears tend to expand out in the middle under acceleration and the fronts of course do not. If it was not for that, don't you think your fronts would wear out in the middle also?
