TPMS primary purpose is to let us know if we have a hole in our tire since, with runflats, it is not always apparent if the tire has low or no air pressure. Fortunately, TPMS also lets us know when they are very under-inflated. It does not communicate optimal inflation. It could, but the average car owner would think their car has a problem if it asked for air every few weeks.

As stated by someone else, it is a good idea to check the pressures frequently with a gage if you want your tires to last. By the time the TPMS light comes on you have been running for weeks or even months at a lower than desired air pressure. I check mine every two or three weeks in the morning before the car is driven. I may have to add 0.5 to 1.0 psi instead of the 8-12psi required once the TPMS light comes on.

 

You can definately tell when the runflats are flat, if you are paying attention at all. My wife can see the difference in the tire by the time it gets down to about 20. I can feel the difference in the way the car drives long before then. I'm not saying we are special, just that if you look at your tires carefully and pay attention to the way the car is handling, you should be able to tell.

 

I agree... paying attention is definitely the key to preventing most major car problems. Your friends may be different but a lot of my friends have no clue about cars. The don't call the little lights on the dash "idiot lights" without reason.

If the tire pressure is significantly low, the tire is not wearing as it should with correct pressure. If we go by the door plate (38psi), then wait for the TPMS or until we see the low tire, we will spend a lot of time driving in the <38psi to 26psi range. By checking mine every few weeks, I only vary from 38 down to maybe 36 if the weather turns cold.

 

Does anyone know if a dealer will fill up your tires for free? My light came on and I have a gauge but I lent my bro my portable inflator for his "new"/used car (Mustang running Z-rated tires and had to replace them 2 weeks after buying because they would hold air for barely a few days..) and never got it back My dealer that I purchased from is only a couple of miles from work so I was thinking about blowing in during lunch tomorrow.

It's gone from 50s to 20s pretty much overnight here which caused a bit of a drop in my front tires, backs seem okay, but I tried to reset the light and it stays on, soo

 

TPMS reset itself?

Yesterday morning, TPMS came on at start up (was around freezing). was sure it wasn't flat coz i usually keep the pressure at 36psi for a gentler ride on the run-flats. pulled into a gas station a few blocks away, warning still on. all tires were down to 30psi each so i filled them up to spec 38psi (17's). in my rush, i forgot to reset the TPMS. i was already on the highway when i realized, no more warning on the dash.

 

MINICLUBMAN is on the right path. I researched the specs on the active TPMS on the R56 (2007 in case they changed suppliers ) and here is what it works on.

It stores pressure from each sender when you do the reset routine. The internal trip in the software is supposed to be about 2.2 lbs of pressure. Why that delta was used may have something to do with conversions from european pressure readings to "english" standards.

Heres the process I follow and it seems to keep the sudden cold snap = low pressure warnings away.
1. decide on what pressure you want. either the doors suggested or what you like. The tire manufacturers sidewall has nothing to do with suggested for your car. It's just legalize to save their a$$.
2. set the tires two pounds lower then what you want then do a reset/short drive. You have to cause the tires to rotate to trigger the whole learn cycle.
3. Now readjust the pressure up the two pounds to your desired settings. You have created a four pound buffer this way and a twenty degree shift in outside temp will not create a false low reading.

YMMV - and you still should check your tire pressures once a month at minimum.

oh and BTW - for those with active TPMS the senders battery is only rated for 7-10 years according to the manufacturer. All depends on how much you drive as the senders in the tire go to a low broadcast rate while parked and a higher rate while driving. More parked should mean more battery life.