mgfred

One of the things about having all of this technology in the car is that at least during my first month I have checked out the DIC every day and I have found the tire pressure indicator to be pretty consistant when I start off, then depending on how hot it is and how long I have driven the pressure increases.

When I started Saturday morning on the Bodega Bay trip I had the following tire pressures. LR 37 RR 36 LF 35 RF 34 (I had put air in them the 3rd day I had the car based on the Onstar report). Now we drove about 300 miles Sat, with temps as high as 104 (valley) and low as 66 (coastline). Also the road conditions were very poor in some cases, actually the worst for potholes, fractured pavement, etc that I have experienced for many years.

I get my new Onstart report today and the tire pressure is as follows: LR 32 RR 31 LF 31 RF 30. I have never had a tire pressure monitor in a car and usually only put air in my tires once or twice a year. Is losing 5 lbs in the back and 4 lbs in the front on a single day (with temp extremes) normal? Is it the wide tires? The aluminum rims? Our terrible CA roads?

Hopefully as the newness wears off I won't be as obsessed with the DIC as I am now (kid with new toy).

Fred

pitbull76

Was it colder starting out when you got the lower readings? I would bet that it probably was. Since all of your tires lost air at the same rate, it is extremely unlikely that they all have developed a leak. It is probably a change in the environment that you are driving in that caused the pressure drop.

mgfred

The first pressures I posted were Sat morning at around 6AM, car had been garaged for the evening as usual. The second readings were taken yesterday sometime before 3PM, car had been in the garage since the previous day.

Yeah I doubt leaks too, I suspect more that it was the trip Sat. It's just weird that a relatively moderate trip, with temp changes, bumpy roads, mix of city/hwy driving would have both front tires lose 4 lbs and both rear tires lose 5 lbs.....

Fred

masterchief1112

i deffinetly agree that it was the environment. air can fluctuate alot in its volume.

hyperv6

Not just enviroment but also the heat from the front brakes can increase pressure over the rear. I usally see a pound or two incease with my front tires over the rear in city driving.

Snoopy

First, let me say......

Because I have a source to do so, ALL of my gauges, torque wrenches, etc. are certified for accuracy.

The tire pressure report that OnStar transmits each month, is not exactly accurate. I have 2 vehicles with the TPMS system and OnStar. I have discovered that OnStar tire reporting has been inaccurate by about 2psi.........based on my CERTIFIED (to .2 PSI) digital air gauge. Many other forums, dedicated to a specific GM vehicle, have discussed this issue. I have also discussed this with the On Star representatives, who acknowledge the report is only "in the ball park".

According to tire manufacturers, tire pressure will change 1 PSI for every 10 degree change in ambient.........30 psi at 60 degrees will be 33 psi at 90 degrees. Also recognize elevation will have some bearing on tire pressures. Although I don't remember the calculation table.

Be careful with over inflating "low profile" tires. They are more susceptible to blow out if a pothole is struck.

Tire pressures should be established at a cold setting....perhaps after sitting all night then checking first thing in the morning (remember my statement above regarding air temperatures, when your seasonal air temps change).

Good Luck

tireman1554

You must also remember the weather outside plays a HUGE factor on tire pressure consistency, vehicles in very humid climates will tend to lose more pressure than vehicles in lower humid climates. Yea your tires will increse pressure as they heat up, but as they cool you will loose anywhere from 5 to 10 PSI per month that you will never regain. No tire on the planet is impervious to air migration.Tires with a Halobutyl liner loose less air than others with a traditional Butyl liner. Because of todays technology tires do not get near as hot as tires built as little as 5 years ago so the amount of air loss may seem to be more drastic than one you are used to. Another solution is Nitrogen. Yes normal air is made of nitrogen, but the nitrogen that is put in tires is alot dryer and have larger molecules that are not able to migrate as quickly as normal air. Hope this helps.

HHR_ROX_CALI

I'm just going to say that I personally would never trust the tire pressure indicators on these new cars except to possibly detect a very low tire. I've never had them but I hear about a lot of problems-- just seems like they create more "problems" than they solve. I would check them manually with a good dial indicator gauge. If Snoopy says his digital one is good too, I believe him, but I've been taught to use a quality dial indicator.
And Fred, don't get obsessed by your DIC

JoeR

Would you please clarify the issue of molecular diameter of nitrogen vs. "normal air"?

Yes, this is a "setup"!

solman98

On my stock 16's, I would loose about 5 lbs every month for close to a year. Then it stopped.

I have no explanation........

My wifes Mazda, I have never had to add air to the tires except when new tires were installed. It's an 03 model. Go figure.