george_k

Been flipping through posts on tire pressure, I've put 18" Carrera III
wheels on my C2S with PS2's

after reading through posts decided to try 33/39 which seems to be a popular
setting. One thing that I am puzzled by is that many posters do not state whether they are running 18"s or 19's when listing their favorite pressure.

to my point - What is the recomended partial load setting for 18"s ?
and, does it make any difference that the 18"s are installed on a C2S
(probably a dumb noob question)
my door plate shows settings for the original 19's - 37-44 and the only reference i can find for 18's in the manual is for 18" winter tire @ 36f-44r
- considerably off from what everyone seems to be running.

BTW TPMS is a pita, have it set for 18" winter tires and its giving a constant
low pressure warning with 33/39 cold pressures.

GSIRM3

I think you have answered your question regarding why you are getting an alarm if running 33/39. You stated that you have the TPMS set for 18" winter tires, and the manual lists pressure for those tires as 36/44. Those pressures are also probalby in the computer for 18" winter tires. So, if you are running 33/39 and the TPMS is expecting 36/44, you are going to get an alarm if it is doing its job.

george_k

Your right about my answering my own question.
What TPMS setting is everyone using to run 33/39? is that something only available on a C2?

Hopefully I can find a happy medium in tire pressure that won't constantly set off my TPMS alarm.
37 in front is not too bad but 44 in the rears is harsh. Have to RTFM again to find the TPMS loading/size/season setting with the lowest pressure's and try that.

GSIRM3

On my C2S with the 19's, I have my TPMS set to 19", summer tires, and partial load. I run around 34/39 and get no alarms. I am pretty sure the 18's require more air, but not as familair with those pressures since I have 19's. But if you have your TPMS set for winter 18's and the recommended pressure is what you stated in prevoius post, then I think you will get alarms running 33/39.

If Porsche recommends higher pressures for 18's, I would not run the 19" pressures if I were you.

george_k

Can anyone with a 997 C2 let me know what the manual states for normal and light load tire pressures for 18" tires. My C2S manual only shows the info for 19" tires.
Thanks.

helispud

From page 334 of my manual: Tire Pressures for cold tires
Summer and snow tires 911 Carrera & 911 Carrera S
18 inch wheels
front 36 psi (2.3 bar)
rear 44 psi (3.0 bar)

There is no difference for light or full load, as there is for the 19 inch wheels.
This info is at the back end of the manual in the "Technical Data" section.

george_k

Thank you very much

elh0102

George_k, I believe you might be over-thinking this a bit. The "right" pressure depends on what you're doing with the car, and how you want it to ride and/or handle in the process. Handling, ride quality and tire wear will all be generally acceptable within a range of pressures. And other things equal, you will find no significant difference in desired pressure between 18" and 19" wheels. The shorter sidewall of the 19" will result in a bit harsher ride with the same pressure (assuming the same brand/model tire). Some folks prefer less pressure in the 19's on track, because it makes the tire a little more forgiving as it breaks traction. I find my car (997S) with PS2's handles best for me at around 36 front and 38 rear, at operating temperature. Knock 3 or 4 off for cold temp pressure for street driving, and 6 to 8 for track. You will probably end up in the range of 34-38 front, and 38-42 rear, at operating temperature.