Adding air to tires - how much and do I trust what TPMS says?
02-05-2009, 12:30 AM
#17
Racer
Join Date: Oct 2006
Location: San Diego, CA
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Did you find in using your gauge that the differntial from the recommended pressure for the wheel and what the pressure read at the gauge before adjusting, matched with the differentials reported by the TPMS on its differential screen (the absolute numbers page is never intended to use for adjusting any pressures) ?
I got my acronym wrong before. TPMS, not PSM!
02-05-2009, 05:41 PM
#18
Drifting
Thread Starter
I don't know what was in the manuals prior to 2009, but as I've only got the 2009, I'm somewhat amused at the lamenting and hammering of the TPMS system for giving bad pressure readings. The 09 manual clearly states that one should not use the pressure readings on the display for any refilling of tires, they are for approximate informational purpose only. To have folks then say they don't trust the readings just repeats what the 09 Porsche manual is telling me already - the pressure readings are not to be trusted.
What I was after is not if the pressure reading is to be trusted, but if the differential/offset reading is to be trusted. It may be the same issue.. I'll find out this weekend when I bleed off a few pounds of air to match the sticker values.
What I was after is not if the pressure reading is to be trusted, but if the differential/offset reading is to be trusted. It may be the same issue.. I'll find out this weekend when I bleed off a few pounds of air to match the sticker values.
02-05-2009, 05:41 PM
#19
Drifting
Thread Starter
I don't know what was in the manuals prior to 2009, but as I've only got the 2009, I'm somewhat amused at the lamenting and hammering of the TPMS system for giving bad pressure readings. The 09 manual clearly states that one should not use the pressure readings on the display for any refilling of tires, they are for approximate informational purpose only. To have folks then say they don't trust the readings just repeats what the 09 Porsche manual is telling me already - the pressure readings are not to be trusted.
What I was after is not if the pressure reading is to be trusted, but if the differential/offset reading is to be trusted. It may be the same issue.. I'll find out this weekend when I bleed off a few pounds of air to match the sticker values.
What I was after is not if the pressure reading is to be trusted, but if the differential/offset reading is to be trusted. It may be the same issue.. I'll find out this weekend when I bleed off a few pounds of air to match the sticker values.
02-05-2009, 07:03 PM
#20
Burning Brakes
Minok ...
From what I see the differential is not to be trusted either. I've never had the TPMS show the same/same pressures ANYTIME in my ownership ... which is only a week (400 miles).
For example, I may start out from the garage with 27/33 F and 34/37 R showing on the TPMS. After driving a while at below freezing temps ... the TPMS does show that the pressures increase. But, they seldom are the same/same.
And, as I wrote above, I spec'd the tire pressures out and they were what the door sticker recommends (one tire was 1 elb low). But, the TPMS was indicating lower pressures than my gauge was reading and the TPMS was not showing pressures that were the same from Ft/Ft or Rr/Rr.
Soooooo .... I'm not sure what the function of the TPMS is. I'll prolly know if I have a flat sneaker and if the pressure sensors are not accurate, then they are just expensive doo-dads of little use IMO.
From what I see the differential is not to be trusted either. I've never had the TPMS show the same/same pressures ANYTIME in my ownership ... which is only a week (400 miles).
For example, I may start out from the garage with 27/33 F and 34/37 R showing on the TPMS. After driving a while at below freezing temps ... the TPMS does show that the pressures increase. But, they seldom are the same/same.
And, as I wrote above, I spec'd the tire pressures out and they were what the door sticker recommends (one tire was 1 elb low). But, the TPMS was indicating lower pressures than my gauge was reading and the TPMS was not showing pressures that were the same from Ft/Ft or Rr/Rr.
Soooooo .... I'm not sure what the function of the TPMS is. I'll prolly know if I have a flat sneaker and if the pressure sensors are not accurate, then they are just expensive doo-dads of little use IMO.
