HamOnRye

What tire pressure is TPMS set for? Has anyone ever gotten a low tire warning from TPMS?

I'm getting ready for a trip so I checked my tire pressures and found them to be 8 to 10 psi lower than they should be (Mea culpa, I should check more often). Those pressures represent a 20 to 25% reduction to the pressure I entered in TPMS via MMI. I'm wondering why TPMS never spoke up, and just how low the tires need to be before it does.

I couldn't find anything in the owners manual about the trip point for the alarm.

uberwgn

It may be that the "stored" value wasn't set correctly. I agree, I think you should have a warning when things are off by 10psi.


Make sure you are getting your inflation pressures from the Owner's Manual.

HamOnRye

When I entered the values in MMI, it accepted them. I think a warning would have been nice, but it's also good to be reminded that you shouldn't fully depend on the electronics for safety. I bought an engine oil dipstick for that reason.

2015 S5 with 255/35 ZR19's
Full load (4 passengers) = 41 front, 38 rear
Normal load (≤ 2 passengers) = 38 front, 32 rear

I'm trying 40 front, 35 rear for a long freeway drive with just me + luggage.

mikejaeggi

my inflation warning went off last week for the driver's side rear. does the MMI not show the actual tire pressure? I can't seem to find how to view what the pressure is, just a warning that it's low and an then resetting it once I filled the tire back to 42 PSI.

uberwgn

Mike, that's correct. The sensor-less system can't display pressure. I'm quite certain it does tell you which corner of the car is having a problem.


I gather the A8 and R8, with their in-wheel sensors, display location and pressure.

superswiss

The indirect TPMS in the current Audis cannot tell the actual tire pressure. The system learns the wheel speeds and frequencies associated with properly inflated tires and is designed to meet the NHTSA rule about low tire pressure warning. That rule stipulates that the TPMS has to warn about a 20% loss or more in tire pressure on an individual tire within 20 minutes while driving between 35mph and 65mph, or it could be 25mph and 65mph, I don't recall exactly. The Audi system is quicker than that, but you do have to drive at a certain speed.

Also, when you set the tire pressure in the MMI, they don't get set right away. It simply starts a new learning phase and it takes about 20 minutes for the system to learn your new tire pressures, so make sure you keep driving around after setting the tire pressure.

The system mainly helps in detecting a slow leak. It doesn't do much about a sudden loss of tire pressure and it is no substitute for checking your tire pressure at least once a month or better every two weeks.

superswiss

Yes, it does tell you which tire is low. The initial indirect TPMS systems only compared wheel speeds between all four wheels and if it detected a large enough difference it would warn. Which meant that if all tires lost pressure at about the same rate it never detected the low pressure. Today's systems are much more sophisticated and do a spectrum analysis of the wheel speeds and the inherit frequencies picked up through the ABS sensors and can tell if any or all tires are low.

HamOnRye

My TPMS was set at 39 psi for the front wheels when I last filled them over 2 months ago. I measured them at 29 psi yesterday, a loss of more than 25%. They had been driven at speeds between 35 and 65 mph many times for more than 20 minutes. So why no low pressure alert?

TPMS seems pretty worthless to me; I don't think I'll bother resetting the MMI when I refill my tires. Monthly pressure checks and visual inspections all round when pulling into a rest stop are far more worthwhile, safety-wise.

AUDIQSS

Inflate your tires to your desired pressure, set the pressures into MMI, drive around for a few miles, let about 8-15 psi out of any one tire, and then drive around again to see if the system detects the low tire. If the system doesn't detect it, then it's time to talk to your service advisor about checking the system.

superswiss

Did you set and check the tire pressure when the tires were cold? Cooled down at least 3 hours after driving and not driven more than a mile to the rest stop after they cooled down.