Squalo

Please excuse the ignorance, but what happens to the TPMS when you install aftermarket winter wheels and tires?

uberwgn

Squalo, not a big deal. Most of the cars no longer have the in-wheel sensors.

baron37

in my opinion the TPMS indicator in the A3 is antiquated compared with other new designs since many new cars show the TPMS level of each individual tire in the instrument panel which in my opinion is much more assuring having this info available instantly.
red baron

Fixeroh

Squalo; this has been discussed here a bit already but essentially, the sensor is in the hub assembly on the car and not within the wheel itself. You can mount any wheel/tire combo you want. Just manually adjust the pressure in each tire as appropriate then access the TPMS via the MMI and 'tell' the car the pressures are set. The car then remembers these values and will error if the pressure changes by more than 20%.

I agree with baron 37 that being able to see the actual pressure of each tire on a display is cool BUT the wheel based sensors are expensive and fail. They often get damaged when changing tires on the wheel as well. I was happy being able to buy a winter wheel/tire combo and NOT have to screw around with sensors.

uberwgn

^^^ a huge advantage and benefit

Boulders

I had 18" winters (andros R9 / Goodyear ultragrip) installed at the dealership before I picked up the car new in Dec.
I didn't think much about the tire pressure and was glad that I didn't have to see a warning light every two seconds like I did with old A3 3.2 that S3 replaced.
Couple days ago, I blasted a giant chuckhole and could hear/feel that I had blown out my left front tire.
NO WARNING LIGHT CAME ON.
So I guess the MMI never was set? I dunno. maybe someday I will have time to read the F Manual.
PS: the spindly jack handle snapped like a twig during jacking. I want to replace with a beefier jack. any ideas?

uberwgn

Yeah, that's the downside of the newer TPM system. It's slow-response compared to the system that utilizes the in-wheel sensors. Your tire was probably on the ground before the system could determine there was a problem...

joxer

I did not realize they had upgraded the TPMS to 2002 Mini levels - that was exactly the way it worked on our old Cooper S. I'm a recent visitor to this part of the boards considering an A3 to complement my 10 year old A4 Avant so I didn't know this had been discussed on here. I may now consider getting it. If you have a complete blowout and don't realize it I don't know if a warning light in the dash will grab your attention either ;-).

Fixeroh

As I understand it, the A3/S3 hub oriented TPMS works off a vibration or frequency through the ABS somehow. I'm an engineer and still don't get it. Once you inflate your tires to the same pressures and tell the car they are set and equalized, I guess the car learns what the frequency of the rotating wheel/tire is at that point. I assume as a tire deflates, the resonate frequency then changes and after a certain point, declares a warning to the driver. A massive, instantaneous blowout doesn't give the system that option. Not sure any TPMS would be of much value for that scenario.

To me, TPMS is a system big government forced on the auto industry as a mandatory feature to keep tire pressures close to correct in order to increase overall fuel economy. I really don't think the thought was for overall safety or for our convenience. I'm old school and used to frequently checking pressures with an accurate gage. And after spending some time doing amateur racing years ago, I can feel when tire changes by a few PSI. At least I think I can feel the difference. Don't remember the last time I had a flat either.

Also, using a system as we currently have, we are not forced to use the pressures stamped on the door jam plate. Wheel mounted sensors are often factory set to a certain level and if it varies by a few PSI, you get the buzzer. Our current system allows you over or under inflate a bit without penalty. And you won't get a bunch of false alarms either. My daughter has a fairly new Mazda and the her TPMS is constantly acting up in the cold despite the pressures being spot on.

uberwgn

FMVSS 138 is a regulation created by the National Highway Traffic Safety Administration (NHTSA). The objective of this regulation is to alert drivers if the pressure in a tire is down by 25%. All vehicles built since September 2007 are required to have a tire pressure monitoring system (TPMS). As Dr. Thomas Roscher, development engineer, Tire Pressure Monitoring Systems, Product Quality Assurance, Audi of America, points out, in Europe, where there isn't an FMVSS 138 on the books, drivers tend to check their tire pressure every two or three months. In the U.S ... well, let's just say that the frequency is not that high.

Early on, when the regulation was being developed, it was thought that there would be two ways to accomplish the necessary TPMS functionality: direct and indirect. The standard is really technology neutral. The issue is accomplishing the task, not stipulating how it is to be accomplished.

According to Urban Forssell, president and CEO of NIRA Dynamics AB (Linkoeping, Sweden; www.niradynamics.se), the first generation of indirect systems, of which there were a handful in production, "had in common a comparison of wheel speed pairwise. You make an assumption that only one tire at a time loses air, and you make the comparison." He points out, "If all four tires lost air at the same time, you'd never know it."

Consequently, indirect TPMS generation one didn't cut it since FMVSS 138 also requires pressure loss detection on all four tires. So all vehicle manufacturers have opted for what is a more straightforward approach, which is the direct TPMS. What this means is that there are pressure sensors mounted inside each tire; there is transmission of that information to a processor that then activates the alert if necessary. While this approach certainly meets the requirements, Roscher acknowledges that drivers pretty much don't care whether their TPMS system is indirect or direct--until there are some changes. For example, the driver may decide that he wants to swap summer tires for winter tires. Or the driver wants to buy some new tricked-out wheels. Or the batteries in the sensors run out. All of this results in additional charges to the customer. Not only would there be the cost for new sensors for the new tires or wheels, but also the additional cost related to the service at the tire dealer, as the regulation stipulates that the tire dealer and the customer are certain that the TPMS system works as required after any changes (e.g., this may necessitate a calibration phase during which time the vehicle would need to be driven, and undoubtedly hourly rates would apply).

Audi is opting for the indirect route. That's right: indirect TPMS. Although the generation 1 approach didn't work, NIRA Dynamics, which didn't participate in that technology, has developed a software-based system that, explains Forssell, has sufficiently robust algorithms such that it can handle the NHTSA requirement of detecting 25% of tire pressure loss within 20 minutes while driving at a speed of 31 to 62 mph; the detection time is generally much faster than NHTSA's 20-minute requirement. There are no wheel-mounted battery-powered sensors. No radio frequency transmitters or receivers. Rather, the NIRA Dynamics system, designated TPI (for "Tire Pressure Indicator"), makes use of the wheel speed sensors that are part of the antilock braking system (ABS) and electronic stability control system (ESC). A processor is needed as well.

"Wheel speed sensors have been around since the introduction of ABS, and have proven to be mature, stable and reliable," Forssell says. They are used as input to the NIRA Dynamics software. At first, the processor that will make the calculations is a stand-alone system. For example for the '09 Audi A6, there will be what Roscher describes as a "little gray box." That's the processor. "Eventually," he says, "it will be integrated into the ESC processor." It is simply a matter, going forward, of making accommodations for the indirect TPMS system in the controller.

Essentially, the NIRA Dynamics TPI system "learns" the radii and frequency characteristics of properly inflated tires. Then, it is able to detect whether there are deviations from normal, which would be a result of the loss of tire pressure (e.g., when a tire loses pressure, there is a change in the radius as the tire rotates, which has a consequent effect on the measured parameters). The system can detect a change in any or all of the tires (remember that the previous indirect systems measured pairs of tires unlike this one, which has inputs from each of the tires).

Because there aren't additional sensors, there is less cost and complexity with this system, Roscher explains. He goes on to point out that there is a customer benefit because as this is a software-based system, when wheels or tires are changed, all the driver and/or tire dealer needs to do is recalibrate the system (this essentially consists of selecting a reset function, then driving the car with properly inflated tires-period). Forssell adds, "You can change and even supersize your tires and the system will learn about them."

According to Forssell, Audi is the first vehicle manufacturer that is standardizing on this indirect TPMS system. It is anticipated that the full lineup of Audi vehicles will be equipped with the system by the 2011 model year.


Mfr link: http://www.niradynamics.se/scripts/resource.php?id=11