Planet-9 Porsche Forum banner
  • Hello Everyone! Let us know what you would spend a $50 Amazon gift card on, HERE For a chance to win a $50 Amazon Gift Card!
1 - 18 of 18 Posts

·
Registered
Joined
·
50 Posts
Discussion Starter · #1 ·
Just got a new Cayman S with 20" tires (Pirelli 265/35 zr20 95Y) from a dealer in Chicago and when the car was delivered, the tire pressure was like 40 psi for the rear tires. The door panel said it should be 33 so I let the pressure down. Then a few days later I had to take it to the local dealer for a minor issue. When I got it back, the rear tires were at 45!! lbs. So I've been trying to figure out if the official-unofficial recommendation on tire pressure is to go 40+ on the rear wheels but haven't gotten my emails to the dealer answered yet. I am about to take a bit of trip in the car Friday and so was hoping to get some feedback from the community.
 

·
Registered
Joined
·
268 Posts
I'd be believing what Porsche and Pirelli say and put on the door panel. That's what I use.

Measure the pressure when the tyres are cold (not driven on for at least a couple of hours). Measure them with a good gauge. For 'domestic' use a couple of pounds either way won't make a significant difference--note that the comfort pressure for the 20" wheels (where approved) is 30 psi.

There are various stories about why dealers often set them high but nothing definitive so far. Maybe they can't read.:) It sure makes the car ride hard.
 

·
Registered
Joined
·
736 Posts
A lot of tire shops pump to 40PSI to ensure the tire is correctly mated with the wheel (bead seated).

They should be ~ 30 PSI all round (check with B pillar plaque) at 20 degrees celsius e.g. cold/ not driven
 

·
Registered
Joined
·
271 Posts
My Cayman says 32# all around on the door and in the manual and that works great. I have to drop it to about 28# if I am going on track in the summer so it will get to about 36# hot.

There is a conflict in my Audi. The manual gives very detailed specs for various sized tires and then says to follow what is on the door? The door says something like 40# all around but the book says 35# front and 32# rear. I used the latter and it was about perfect. However, I noticed the tread was wearing slightly more in the center so I lowered it to 34/31. Most of my driving has been on interstates. 35/32 would probably be best for more typical trips.

The interesting thing is why does the manual give all those specs and then say to ignore them? I suspect it may have something to do with Audi engineers vs. US lawmakers. You may need 40# to get the specified mileage, like I care.

Bottom line is I would check the manual and the door. Mine matched; yours may not. In my extremely brief experience the manual would be the one to follow if they differ.
 

·
Registered
Joined
·
2,423 Posts
My experience with dealers and independents is they ALWAYS put too much air in tires, regardless of car brand or tire size. My standard instruction at service time is to NOT check or change pressures as I am very anal about tire pressure and it is already where I want it to be. Sometimes they ignore me and put too much air in anyway. I have no idea why or how but it's been that way for me forever.:crazy:
 

·
Registered
Joined
·
271 Posts
Below is the chart from Porsche. Pressure depends on wheel size, model, summer/winter, and front/rear axle. Pressure measured with cold tires (68 °F / 20 °C).
Okay. This is like my Audi. Is there an additional comment to ignore these and to use what is on the door or does the door match these?

My 2012 had an R addendum that spelled out specific pressures for the car and I don't know how that differed from the main manual.
 

·
Registered
Joined
·
41 Posts
Okay. This is like my Audi. Is there an additional comment to ignore these and to use what is on the door or does the door match these?

My 2012 had an R addendum that spelled out specific pressures for the car and I don't know how that differed from the main manual.

The chart matches the plate on the door of my car. These pressures are what Porsche calls "Standard tire pressure". There is also something called "comfort pressure" which is different from the chart/door.
 

·
Registered
Joined
·
104 Posts
I have a 981S on 20" wheels, running MPSS in the standard 235/35/20 & 265/35/20. My a-pillar and manual say 33 lbs at all 4 corners. If there was a discrepancy, I think you should follow the a-pillar. I have suspensions mods and my p-shop said they recommend 30 lbs at all 4. On hot days (sunny so cal) and running the car hard, this can get the pressure upwards of 39-40 lbs. If needed I will drop pressure until I get to 38 hot, then later add air back as needed to get back to 30 lbs cold.

I do have a good quality tire pressure gauge, and it consistently reads 1 lb lower than the dash board reading from the TPMS. I trust my gauge more.

I have a 2017 M240i with 18" wheels, staggered MPSS 225/40/18 & 245/35/18. the a-pillar recommends 35 lbs front & 39 lbs rear. I think that is too high, so I run 33 & 36 lbs.

Not sure why Porsche wants same pressure front and back on staggered sizes, whereas BMW gives staggered pressures. I assume it have a lot to do with suspension setup.
 

·
Registered
Joined
·
256 Posts
I have mine at 33 all around when cold. However, when I've tried to drop it below 33, when I make full lock turns when slowly making a U turn, the tires seems to be riding on the sidewalls or something, so I brought them back up to 33.
 
1 - 18 of 18 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top