Tire Pressure Sensors

[didi]

I have OE Pirelli 255/40R19 tires on my 2006 A8. For winter driving I replaces them with an 18" set of chrome wheels and 235/50R18 Nokian Hap. The Nokian tires are great for Quebec winter driving. Unfortunately I don't have tire pressure monitoring sensors on the winter wheels...thus the annoying sensor warning. My dealers don't know how to turn it off. Any advice/comment would be much appreciated. Cheers

[fuelsaver]

Well you can get some tire pressure monitoring sensors on the winter wheels.

[Ecmbuster]

Quote:

Originally Posted by didi

I have OE Pirelli 255/40R19 tires on my 2006 A8. For winter driving I replaces them with an 18" set of chrome wheels and 235/50R18 Nokian Hap. The Nokian tires are great for Quebec winter driving. Unfortunately I don't have tire pressure monitoring sensors on the winter wheels...thus the annoying sensor warning. My dealers don't know how to turn it off. Any advice/comment would be much appreciated.
Cheers

That's because you can't turn a safety feature off in the normal fashion. VCDS Can disable it because of what you need to do. Wheels with TPMS can be setup on the existing system and adapted easily using your MMI. Read the book.

What you should be aware of is this. Measure the circumference of your original tires and match the new setup with something very close. If you don't, expect the speedo to read incorrectly and the ABS controller to do the same.

[Red G8R]

If you have direct TPMS then you will need 4 sensors/valves for your winter wheels. I ordered 4 from Tire Rack for my other car.
Wheel diameter only applies to indirect TPMS.

[Ecmbuster]

Measure the circumference of your original tires and match the new setup with something very close. If you don't, expect the speedo to read incorrectly and the ABS controller to do the same.

Here's an English calculation.

The formula relating road speed and engine rpm is

mph = (rpm X cir) / (gear X final X Eighty Eight)

where rpm = engine rpm
cir = tire circumference, in feet
gear = gear ratio of your car
final = final drive ratio of your car
88 = combines several conversion factors

For example, an Audi 90 Quattro. Its tires are 195/60VR-14, so the calculated circumference works out to be 72.92 inches or 6.08 feet. Its final drive is 4.11:1, its 5th gear is 0.79:1, so their product is 3.25 and the rest is a quick calculation away:

mph = (rpm X 6.Zero Eight) / (3.25 X Eighty Eight) = 0.0213 rpm

Ie: the Audi will do 21.3 mph for every 1000 rpm in 5th gear.

To work the equation the other way and to find engine rpm for a given road speed, you want to solve for rpm:

rpm = (mph X gear X final X Eighty Eight) / circumference

At 60 mph, the Audi is revving a calculated 2822 rpm, within a few percent of the computer's calculated 2750 rpm.

[ok2000A8]

I think the 2006 A8 has direct pressure sensors inside the wheels, so no need for calculations. Red G8R is correct in assessing that for direct pressure read sensors, all you may need is additional, newly installed sensors that radio transmit the pressure reading. These sensors will need to be compatible with the TPMS receiver so that will neeed to be examined. Older systems measured pressures by counting tire revolutions/rotations compared with other wheels. Low pressure meant more rotations so an alarm was generated. No exact pressure reading was provided. That was how indirect systems operated. Direct pressure reading systems circumvent all of these problems. I'd order the OEM pressure sensors to ensure compatibility with the MMI/TPMS system in your A8. Ask dealer but check around for aftermarket parts as well.