Originally Posted by dongold
My old GT did not have the TPC feature. The new one does, and when reading about it in the owner's manual, I was surprised to see how accurate this is supposed to be.
It seems the readout is temperature compensated, and if I understand correctly, the implication is that this is accurate enough to use as an adjustment standard. They even give an example showing that if adjusting pressure, you should merely add the difference between what the display shows and what the value should be, disregarding the actual readings on the external pressure guage!?
If this is true, then here is my question. When I rode the bike home from the dealer, in very cold outside temperatures, the display showed 46/48. If this is a "temperature compensated," accurate readout, does that mean I should have pulled over, and bled out enough air (even though the tires were now "hot"), so that the display would show close to 36/42???
Normally, I would not bleed air from a "hot" tire, but if the info in the owner's manual is to be taken literally . . . ?
I can't answer your question directly, but here are things that I do know, based on actual experience:
1. Each morning, as my tires warm up, the TPC (TPM) readout increases by 1 (rarely 2) psi in each tire. My guess is that the metal wheels and rims are still cold near the TPM, so the TPM isn't getting an accurate reading of the true air temperature inside the tire.
2. According to the dealer, the TPC readout is 3 psi too low in each tire, compared with their calibrated gauge. Apparently a 10% difference is "within acceptable margins" for the TPC readout. I have seen many posts from others on these forums confirming that assertion.
I note that the TPC matches the several cheap digital gauges that I have. This implies that my cheap gauges are also 3 psi low for GT tire pressures. Nevertheless, the dealer insists that their pressure gauge is right, and they see a lot of GTs that have TPCs that read lower than actual.
If true, that implies that the TPC low pressure warning may appear on a cold morning when the actual tire pressure shouldn't otherwise trigger the warning. Others have reported this issue on the forums as well.
3. The TPC has been VERY consistent for me. That consistency allows me to depend on the TPC to check tire pressures instead of the manual approach, which loses air each time I check. A TPC is a "must have" feature for me, especially because I ride nearly every day.
4. Different riders deal with the TPC accuracy issue in different ways. Some make sure that their TPC reads correctly (36/42) even though they know the actual pressures are a little high. Others learn the TPC readout that yields the correct pressures in the tires.
For me, I still wonder why the OBC can't be tweaked by the dealer to give correct TPC readouts.