jeffrec

Do you guys rely solely on the TPMS system to monitor your air pressure or do you also use a tire gauge? The reason I ask is that I inflated my tires last night because the pressure was low (based upon my tire gauge) given below freezing temps in Atlanta. Today when I drove the car TPMS showed my pressure +8 for each tire. The car seemed to ride a lot harsher as well so when I got to work I let some of the air out and reduced the pressure to +4. Am I running with too high air pressure? Do you all run at 0 on TPMS? Can anyone help explain the variance between the tire gauge and TPMS? Thank you in advance.

Mork

My TPMS and a tire gauge are in close agreement. If the tires get warm, as you would expect, the pressure will increase. Did you compare the TPMS and gauge readings when the tires were cold? The recommended cold pressure (37/44 psi) does give a little bit of a harsh ride.

BIG smoke

I have a few gauges. Stupid things all read differently. $2-$40
I don't have TPMS on my 997.
Good. Because it would cause more confusion.

jhbrennan

I use TPMS as a guide - TPMS doesn't measure same pressure as my handheld but at least the errors are all the same so I can tell differentially if the pressure has changed. I set F/R at 34/40, TPMS reads 31/37 so as long as I continue with 31/37 I feel comfortable. With the big chill blowing through here the last couple of days I've re-adjusted with the handheld to get back to correct psi.

myw

^^ my 997 also has no tpms, its a PITA i do check once a month on all cars 'just in case'. 39/44

there was a time when i lazy and the rears on my c2s had like 28 psi and i drove like that for 2 weeks, WORST milage ever.

our winters can get pretty cold here, if the temperature drops a few degress, i check the tire pressure right away on all cars (tpms or not) and end up needing 3-4 psi each tire.

slicky rick

We have 37/44, 39/44, 34/40. Are we all driving 997's here? How come there are different tire pressures... Are we all talking about oem tire sizes? 34/40 here on 235 and 295 tires.

myw

LOL!.. i think oem for oem 235/295 is 38/44 in the door jam of my c2s.

USMC_DS1

It's a matter of calibration. The only way to determine that your TPMS and/or tire gauge is accurate would be to have it calibrated or use a source that likely is calibrated. I had my p-dealer mount tires recently and used their shop gauge as a calibrated source to determine that my TPMS was within +/- 1lbs vs. my Porsche branded gauge which is consistently +4 lbs... since a usable gauge provide I factor in the deviation.

slicky rick

So we are saying the tpms on our cars can actully be calibrated by the dealer piwis? I did nit know that...myw door jamb says 34/40 on mine like jh's...is it different for .1 and .2?

USMC_DS1

Don't know about that... but the dealers tend to have calibrated gauges whereas I'm too cheap to pay for calibration off my own gauges. Calibration would cost more than my gauges are worth. In my case, my TPMS is w/i a lbs of their gauges so I'm going with that.

myw

i stand corrected, 34/40/ & 37/44 is what it states on mine.... i just checked.

i normally run 39/44 so i guess i have been running slightly overinflated.

jhbrennan

Not everyone runs the psi's on the door jamb. Some adjust for full load, others for half load, winter tires, summer tires, comfort, performance, etc. But the various psi's are all within an acceptable range.

tomc66

You list two sets of air pressure 34/40 and 37/44. Why two? My door reads 37/44 on my 2011 4S. My TPMS reads the same as my digital air gauge.

jhbrennan

Door jamb just has full load pressures. Owner's manual list full load and partial load.

seahull

I just set my pressures to 35/40 on Saturday, as they had dropped this week due to temperatures. But then I looked at the TPMS and it read 31/34/36/39 on the four tires. I drove a few miles
at speeds under 40 and looked again and TPMS read 36/35/45/42. Checked with two handheld gauges and they read within a pound of where I had just set them.

I've only had a car a few weeks, but I now am convinced that I cannot rely on the TPMS, except for +/- 20% measurements. Not worth fixing, as I can check with a gauge and rely on TPMS to tell me when they're flat.