TPMS Fact I didn't know
 

Took the Q5 in for camera, and while there inquired about why the TPMS did not indicate when wife got flat (that's a different post!). As I knew, the system works by noting the difference in rotation between the tires. A difference being interpreted as different pressure. What I didn't know was that (according to the dealer) it takes about 3 miles of driving in this condition before it will alarm.
Makes sense in a way, as you wouldn't want minor changes due to temp setting off the signal. My Acura drives me crazy every year when the temp drops below freezing.
By about 3 miles, my wife had shredded the tire and was parked, so no alarm. Anyone else heard this story?

I had not heard that but it makes sense.

The trade off is that the old system had sensors that needed to be used and meant another US$100+ per wheel if you used a set of snow tires and wheels. Also these sensors were ruined if you used the tire sealant. They also have a internal battery that requires you to replace the sensor when it dies.

Wow - sorry...
I've not heard of it happening elsewhere either (thank goodness !)

would think there would be other 'indications' if you had a tire go way down quickly - like handling issues, 'squishy' feeling...

Like my Dad used to say
"How did we do it before(fill in the blanks)came along?!?"

we are SO spoiled aren't we :) :)

Yeh, she said it did feel a little "funny" and the sun roof rattled. Makes me think if she hadn't stopped at the grocery store she would have driven it until the rim wore out. We have had subsequent discussions!

lol

Unfortunately my 09 has the in wheel tire pressure sensors so I had to buy 4 for my winter wheels at $60 ea. However my previous BMW X3 had the system based on the abs wheel sensors and measuring the difference in rolling diameter but it told me a tire was low within a few hundred feet. Temp variations would't be an issue because all the tires would vary equally. The system should only measure the difference between tires if one is low.

Not an expert, but think the variation is not between wheels, but between what the MMI is set at when initialized and if it changes later...

my thought was that when you selected the "Tire Pressure is right" option, it recorded the revolutions per mile and then if the revolutions varied by more than some factor it warned you....

and would think it's for each tire....

is that not correct ?

As a note my neighbor just bought a new 3 series wagon and they are back to using sensors in the wheels.

The Audi system currently being used is actually ridiculously fancy and monitors "abnormal vibration" as well as rotational inertia. It's supposed to be able to detect slow leaks from all tires at once, or a sudden deflation of one tire.... Supposedly within the NHTSA's requirements on sensored TPMS.

Also, though not exactly related to the op's original question, the TPMS only says something like 'tire pressure is low, check all four tires'. It does not tell you which tire is low. If I didn't have a tire pressure gauge in my glove box a few weeks back I would not have known which tire was low (aside from eye-balling it which isn't always accurate)... Not sure why it doesn't just tell you which tire.

IMHO this type of TPMS is practically useless. What good is it if it does not tell you the exact pressure in each tire at all times. The system is only in place to meet federal regulations. I understand that an in-tire system is more costly in terms of ongoing maintenance and if wheels are swapped but to instantly know precisely what your individual tire pressures are is much more valuable. The system in my Acura is very accurate and reacts to pressure changes very quickly. I have checked it against a high end digital guage and it is spot on and has been that way for the past 5 years.

Doesnt BMW have run flat tires? It has to use a direct tire pressure sensor since the sidewall is so stiff.

When my wife got a nail in her tires a year ago, the Q5's indirect TPMS told her which tires were low.
In my opinion, Audi's indirect TPMS works very well. Some earlier version of the indirect TPMS from other manufacturer did not work well at all, but Audi's version of the indirect TPMS is pretty advance. My wife's new car has those direct TPMS that tells her exactly what the pressure is on each tire. It’s sort of an information overload in my opinion. If one of the tires is low, I tell her to check all the tires. I prefer the simplicity of the indirect TPMS system over the complex direct version.

My BMW motorcycle has a sensor in each wheel with a digital readout on the console that shows (relative) pressure in each tire. It also triggers an alarm when a tire reaches a certain minimum safety threshold. It compensates for temperature changes and ambient pressure. Very accurate to the degree that I can fill the tires using the pressure sensor readout and the pressure will be correct at any temperature.

Now THAT is the only system I deem worthwhile. Three miles is way too long to trigger the alert, but then as a poster stated, "what did we do in the old days" without all these newfangled things?


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I had recent experience with the TPMS. I somehow got a puncture in the tread but left no nail or anything else to tell what it was. I normally keep the tires at 35 psi, however, due to this puncture, I was losing 12-15 psi over a 12 hour period. My TPMS notified me within the first mile that I needed to check my tire pressure. You can always test the system by lowering the pressure and take a drive to see how far before you get the warning.

Is the TPMS sensitive enough to trigger the alarm during freezing cold temps? I live in New England, and it's been very cold the past couple days. I was driving yesterday and the alarm came on to check all 4 tires. By looking at the tires, they look ok. Going to check them today. I know the the PSI in tires goes down in the winter time because of the cold temperatures.

the TPMS was triggered on our A4 during the heatwave in Philly where the temps reached 110+. I stopped, and checked all the tires, they were above normal PSI, but all were the same, except one that was 1 PSI different. If extreme heat can make it go off, I'd imagine extreme cold could as well.

Mine did that too when It got cold. After checking the actual pressure in the tires I just reset the MMI tire pressure setting to recognize it. (2010 model, no in wheel sensors)

The indirect TPMS used cannot tell you which tire is low AFAIK. In worst case scenario, if you have one low tire, Audi wants you to check all the tires (something no one ever does and was usually a weekly check for any automobile). The system works, but it will need you to drive, for it to read the low tire. If you drive slow through a neighborhood, it may not come up as quickly, but there is fine line between over compensating with false triggers and actual low tires, so keep this in mind. Actually, if you had a really low tire or flat tire, you should notice that immediately, but I have seen people drive until a wheel falls,off from a locked up wheel bearing on another brand vehicle until it broke the spindle end, so not everyone is in-tune to their car as we expect them to be.

It does tell you which tire is low. At least in my '11 Q5.

I had it confused with TT and R8 systems, that why. Plus those have sensors, DUH, LOL! Forgot on the sensorless TPMS, it shows the warning in the instrument cluster, you just can't view actual tire pressures. Way too many systems for me to remember lately.

I had a nail in my tire (2011 car) about two weeks ago and the system did tell me which tire to check. We had a screw in the tread of our Avant last week, I don't believe there was any indication which tire was at fault.

The sensor-less system is not nearly as sensitive as the in-wheel sensor based system. You have to lose quite a bit of air in the newer system before it triggers.

We had a slow leak on one of the tires on our Q5. The warning light indicated a particular tire was low on air. When I check the the pressure it was 28 PSI, the rest of the tires was 34 PSI. Audi's indirect system works very well compare to some of the other indirect system I have had.

Not completely true to the all equal variation!
I had parked once in a space that there was some snow only on one corner; being parked in the snow on just that one tire had caused the sensors to alert to me to the off-pressure.
Now how being in that snow affected the 1 tire I cannot explain! but it did.

If you had one tire in the snow, it would reduce the pressure in that one tire.