Okay, maybe old and maybe new, but here are my questions regarding my Cayman's tire pressure and the TPMS.
1. If my garage temperature is 90 degrees, to what extent (how much) do I adjust the psi in my tires up from the recommended 30/31?
2. If correctly adjusted, say up to 32/33, will the TPMS still show 30/31, having taken into account the higher ambient temperature?
3. Related to number 2, above, if my tires are correctly inflated (e.g., 30/31 at 68 degrees or adjusted per number 1, above), will the TPMS always show 30/31 despite the ambient temperature rising or having driven the car at higher speeds for a period of time?
4. If the ambient temperature goes down to well below 68 degrees (thus lowering the psi from 30/31) should I reinflate my tires?
5. Is the TPMS calibrated to 30/31 at 68 degrees or do I need to do this myself?
Please note that all my questions assume no air leaks.
Thanks for all input.
My TPMS always seems to read pressures 1-2lbs higher than my tire gauge, but the TPMS pressure readings do drop consistently with drops in ambient temp. Since I don't like to over-inflate, I always seem to be on the verge of tripping the low pressure warning. As ambient temps cool in the fall, I have to add air to keep the warning light off. Not sure if that addresses your questions but that's my experience.
My TPMS is consistently 2 lbs lower than my gauge readings so I compensate for that whenever I look at the numbers in the dash.
Don't go nuts with adjusting the pressure for normal street driving. During the summer (80F degrees avg. temps) I make sure my cold pressures in the AM match the door jam sticker. The tires will heat up during normal driving but I don't care as long as my cold pressures are correct. As long as I don't start seeing 45+ PSI on the tires during summer driving, I don't worry it.
Once the avg. morning temps drop below 60 degrees F, I add a pound or two to compensate. Once they drop below 40 (I don't have winter tires), I pump them up again a bit.
To make a long story short, my experience has shown that 40, 60 and 80 degrees ambient temps are good cutoff points to adjust your cold pressures to match the recommend numbers on your door sticker.
Well, to be precise, 20 degrees F is another cutoff point but I was afraid the plastic clamp on the air pump was going to snap off trying to refill at those pressures. And the summers tires become hockey pucks as well at those temps.
Now this is all for normal street driving. Adjusting pressures or optimal grip between track sessions is a whole other can of worms...
My TPMS is a good 7-10 lbs low. The dealer insists there's no way to correct this. Remember, this isn't a Porsche feature, it's a government requirement so it has to work within their stupid parameters. Don't rely on it for any kind of accurate reading, mine tells me I have a flat tire at 35psi.
7-10 lbs low is nuts IMHO.
I wonder if there is an issue with the receiver unit in the car or the transmitters in the wheels.
Thinking about it more, maybe the receiver is the culprit, how could 4 different sensors read low? There must be a way to recalibrate this via the dealer service tools. Very disappointing.
Tires should always be checked with a quality guage and inflated to the door frame inflation sticker number (unless you've swapped out your wheels for a different size than those that came from the factory). There is no manual calculation or ajustment necessary when you inflate them. As Pete said, they should be checked regularly as colder temperatures affect the readings but even then, just reinflate to the door sticker values. In other words, as the temperature drops, so will your tire pressure readings. Reinflate to the normal settings. Do yourself a favor and don't over complicate it. No math required.:banana:
