SMac770

Audi uses a TPMS system that has no clue what your tire pressures are. You tell it "my pressures are correct" by resetting the system, and it takes the relative rotation rates of the tires as "correct". Audi assumes one of the tires must be low if there's a difference in rotation between two wheels on the same axle. It's a **** poor, but legally sufficient, system.

I'm looking to pick this up at some time to put on the car and see how it goes:

superswiss

This incorrect fact gets unfortunately repeated over and over again. That's absolutely not how it works anymore. As I explained above and as you can read in the linked Wikipedia article, the current indirect TPMS systems do not measure difference in relative rotation. The current systems perform a sophisticated spectrum analysis and can tell if any or all tires are low. The very first indirect systems worked as you describe. They indeed simply measured relative differences in rotation, however, the problem with that was that if all four tires lose air, then these old systems never detected it because there was no relative difference in rotation. These old systems have long been replaced with the more sophisticated systems.

Indirect TPMS is more than sufficient for the average driver. For the average driver, the measured tire pressure is only meaningful while the tire is cold, so the readings from direct TPMS is only useful for a brief moment before the tires start to heat up. Once the tires are warm, the numbers are useless. Unless, you track the car. On a track you may wanna monitor the hot tire pressure and adjust it and also monitor the temperature of each tire. That's why Audi is now starting to offer optional direct TPMS on their RS models and the R8. Total overkill for an A4, though.

SMac770

It's still guesswork instead of directly measuring reality. Even the wiki page makes clear that it's guessing there's an issue when inputs differ from the recorded first bit of driving after a reset (for second gen). I prefer factual data when it comes to safety topics.

When my blipped and I checked my tires, the left rear was down from 34 to 25. Then another time I checked and it was 28 but no light. 28 is too low. 25 is way too low. The tolerance on the system is too slack. But it's a 2009. Seems that was a time of change in the system Audi was using.

And the numbers are useful if you're filling up your tire. My nephew has a slow leak in one tire on his Camaro. He just turns on the dash and hooks up a pump. Stops when the dash says the tire is at the desired pressure. If GM can do it, Audi can do it. This is not an economy brand.

superswiss

All TPMS is supposed to be is a safety net. It's not a replacement for checking your tire pressure with a proper gauge at least once a month and visually inspecting your tires for damage. Better yet every two weeks. A typical tire loses about 1 psi per month if the temperature stays the same. If there are large temperature fluctuations than pressure should be adjusted every time the temps drop a lot or increase. If you were down to 25 from 34, then you either have a leak or you neglected to regularly check your tire pressure.

Aviator6

On a positive note, with Audi's TPMS system, you don't have individual sensors in each tire, so much less hassle swapping tires/wheels.

VM

And that's the only excuse/advantage for this system.

Does anyone remember the Nissan commercials from a few years back where the car would honk once you reached the right pressure? If they could do that in an Altima or Rogue or whatever that was, there's no reason a car that costs twice as much can't do it too.

Not to mention, having had it go off on me once, it would have been nice to have gotten some indication as to what was going on instead of just a generic tire pressure low warning that didn't even identify the problematic tire.

lowjdml

That's interesting. When mine went off, it clearly stated 'driver's rear' tire.

Turbo Freak

Audi tpms is the best for places where you have to put Winter tires. I have a friend who has an Honda CRV and he needs to go to the dealership every six months go have the tpms reprogrammed for his second set of tires. Most people do not bother with this and drive all Winter with the tpms warning light on.

IMYM

Second this. Had a car with direct tpms and i decided never to get another one with them. The hassle with winter tires far outweigh any other "benefits".

SMac770

Was getting a tire leak fixed today. Asked the guy about TMPS since I notice I paid $32 for TPMS service kit when I get new tires. He said the newer cars don't have the sensors on the wheels so there is no TPMS kit or cost. So another cost reduction victory for the new method.