fritz:

I'm on my second TPMS car now and have never had any problems as a result of working on the assumption that the system is accurate. At least, not since I took the trouble of reading and understanding the manual, and then using the "pressure difference" display to set the tire pressures. Smiley


1. If you try to adjust the car to what you think feels right, then I agree, it does not matter what "true" tire pressure level is.

However, what I was trying to do is hold the tire pressure at "reference" level -- what Porsche and Michelin think it should be -- so that I could adjust the rest of my suspension components.  I want to set it at true 0 and the compulsive me feels a true 0 requires a reference tire gauge. http://www.longacreracing.com/catalog/item.asp?id=982&catid=8

*Assuming* the Longacre Racing is more accurate, then I did find that TPMS in my car is off by 1 psi in 3 tires (TPMS reads 37, my Longacre gauge reads 36), and off by about 1.5-2 psi in 1 tire. I didn't want to confuse the issue for Alex earlier, but actually in my car the differential setting varies between 0 and minus 1. I hope my thinking is correct here!

2. There is a second way to test accuracy of TPMS, without using reference tire gauge. If you have a tire gauge that is reasonably accurate from reading to reading (and most tire gauges are very much so): Set, say, the 2 rear tires so that TPMS read the same, at for example 37. Now using the tire gauge, measure each of the 2 tires. If the tire gauge reads different values between the 2, then you've proven at least one of the TPMS device is wrong.

I think I am a little nutty. Smiley



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Regards,
Can
997 Turbo + Bilstein PSS10 (Review) + Cargraphic Exhaust (Heavenly Race Car Noise Smiley Review)