ADias

Why is it that PAG used 34/39 for the 997.1 and now says 34/40 for the 997.2 (19" rims) for the 2WD cars?

And... recommends 34/37 PSI for the 4WD 997.2 models...

See your Owners Manual towards the back (depends on manual year pg 289 or 292).

Note also that the cold ref temp is 68F.

mdrums

I asked this same question to a Porsche rep at last yrs 48hr race.....Fuel mileage type of deal....less rolling resistence and handling does not suffer. Run on the street at 33/39 or 34/40 cold not a huge deal.

Did you noe what GT3 tire pressures are?...a lot less....some due to the semi R Comp tire compound and mostly due to handling.

Eric - Plug Guy

More pressing: when using an accurate tire gauge, what's the delta b/w your gauge and the readout when you drive off on the TPMS?

I check cold pressures and find 3-4 lbs lower on TPMS in the front, as much as 5 lower on rears.

Leader

My TPMS readings were consistently lower on all four wheels, compared to my hand-held TP gauge (which I believe to be very accurate).

So, I cold inflated all four tires to the recommended pressures, RESET the TPMS, and now it agrees with my gauge. Maybe, try that?

Fahrer

My TPMS reads one psi higher than my gauge.

mdrums

My 09 TPMS is accurate. I use a $124 Longacre calibarted gauge.

ADias

The GT3 (owners manual) pressures are: 29/31. The car weighs about the same. It comes with Michelin SC and that could be the reason - softer, faster-heating compound.

But I cannot understand the diff for the Carrera S and the 4S:

997.2 S - 34/40

997.2 4S - 34/37 - same tires, heavier car...

What's going on?

ADias

When set with an accurate gauge (AccuTire) the TPMS matches in my car. The 997.2 TPMS works well. The TPMS settings, must be correct in the OBC, of course.

Edgy01

The manuals make no adjustment in their recommendations for a particular tire brand/manufacturer. (Otherwise, every time you change tires you would have to call Porsche for guidance).

kyrocks

My '09 C4S Cab owner's manual and door sill state 37/44. (19" Michelin PS2)
My '11 GT3 states 29/31. (19" Pirelli Corsas)

ADias

That is full load - 4 people and luggage. 2 people and light luggage a 997.2 4S says 34/37.

The point is a 997.2 S says 34/40... why the difference?

Again a different number - perhaps justified on rubber compound, but I am not sure.

ADias

Certainly. Same PSI for Conti/Pirelli/Bridgestone/Michelin, but why the difference between 2WD (34/40) and 4WD (34/37)?

alexb76

Well, aren't they actually different size in the rear? 305 vs. 295?

I know some C2S are ordered with 305 depending on wheels, but I suspect the difference is that ALL C4S come with 305 in the rear, and most C2S come with 295. There's also weight distribution differences...

See below (in Kg - measured by a Japanese test review per each axle), 997.2 C4S is heavier than 997.1 C4S and that, along with different rear tire size might explain why their PSI recommendation is different?!

gpjli2

The different driving dynamics of a 4wd vs a 2wd vehicle apparently are reflected in the tire pressures as you have noticed.

ADias

PAG does not specify any PSI diff between the 295 and 305 rears for the 2WD. The 4WDs are heavier than the 2WDs, therefore one would expect higher pressures, not lower, thus the puzzle.