Sticker on driver's side door jam lists the tire inflation pressures, at least this is the case for my 2018 JCW.

The door jam pressures are for speeds less than 100mph. If you intend to run over 100mph the tires need to be inflated to a different pressures but I don't recall the pressures.

I've experimented a bit with tire inflation pressures ending up 36psi front and 37psi at the rear and I can tell you I think these pressures are a bit too low. I believe they should be 40psi front and 38psi rear and I intend to bring them to the correct pressure Friday AM before I drive to work.

 

I typically just run max cold psi posted in door jam.

 

I know mine were delivered at about 40 psi and that's really up there compared to my old Countryman but I didn't know they were supposed to stay inflated that high -- thanks for clearing that up RockC! Looking at the door sill plate, I swear it says 33 psi but last night after a lot of rain and drop in average recent temps I got a LOW TIRE PRESSURE warning and it still said it this morning. TPMS was reading 36 all around so I thought "What the hell?!" and went to air them up -- thank the Wawa for free air!

 

Did you do an active reset procedure after filling them?

 

I agree RockC. I really think the CM is best with a little more air than the suggested pressures for the car. I think 39 PSI cold rear and 35 fronts works very well. After some driving they heat up to 40 rear and 36 front. I have 7200 miles on there Goodyears and they are wearing very well. I have rotated once. Wear is minimal and very even. I like that, but I think the tires are a little noisy. They are not quiet Michelins .
The air pressure is very stable in these tires. little variance and I think I have only adjusted air pressure maybe once this year.
But I certainly do agree a little more air than the posted is good,
Have a good one !