Hi all –
I'm just revisiting the subject of tyre pressures again on my JCW F54, as I've just had a new set of Pirelli PZ5's fitted.

My car was supplied from factory with non-runflat (thankfully!) Bridgestones in 235/35r19 – this was in late '21/22....Am I right in understanding that all non JCW models had run-flats, plus 18" wheels, or did it vary..?

What I've never been 100% sure about – is the tyre pressure placard (pic attached of mine) in the door jamb specific to your car as supplied or is it a bit more generic..? The sticker here advises 41 & 33psi front and rear, a fair difference. I have had the fronts at 41 in the past, but did find them a touch 'hard'....To confuse matters yet further, the last time I had the car serviced at the dealers, the summary paperwork advised tyre pressures to be at 38psi all-round..! 🤷‍♂️

Interested to know what you folks run your F54 pressures at...?!

Cheers

 

The 2022 owner's manual has 38psi for speeds up to 100mph, and 41psi for max speeds over 100mph:
https://www.miniusa.com/content/dam/...qhVzMrnwsWaQgA

Personally, I would hesitate to run different pressure front to rear. If you are only planning on running on the street and not track driving, I would inflate to 38-40 psi all around, and be done with it.

 

So here's a few thoughts.

1. tire pressure changes depending on conditions - for example my tires on a winter morning may start out at 28 psi with the temperature of 40 degrees.
2. the progress of the day, and the warming of the sun can affect tire pressures significantly - for example those same tires will be 31 degrees by noon even if I do not drive, and 32 degrees if that tire is in direct sunlight
3. driving also adds heat to the tires, and raises their pressures - my 29 psi tire will rise to 33 psi at 40 degrees if I am driving at 80 miles per hour

Consequently, when I think of tire pressure, I consider a RANGE of pressures, ad on any given day my tires will rise and fall 3-4 degrees depending on weather, sun, and driving usage.

For the Continental DWS 06+ tires I run, which are 225/45-17 on a 8" rim, I use the range of 30-35 pounds front, and 31-36 pounds rear. That's a cold starting pressure of 29f/32r @ 45 degrees.

I consider the following factors:
> is my tire adequately supported by the rim? 8" and 225mm are a match, so yes - the sidewalls are vertical which is their strongest orientation, therefore I do not need extra pressure to avoid distortion of the carcass during cornering.
> am I driving at very high speeds? If so, the heat in the tire will tend to adjust by adding pressure, which is good as too much flexion in the carcass due to underinflation can kill a tire
> am I driving on loose surfaces? if so, I may tend to the lower end of the pressure range, as more contact patch and less lateral load will suit the conditions.

Note that I have never, nor will I, use a run-flat tire, so all this guidance is applicable to high performance conventional rubber only.

My tire wear is exeptionally good in this range, providing even distribution across the contact patch, good handling, and good mileage.

Forty one pounds might be acceptable briefly if the day was 80+ degrees and the pace was 70+ miles per hour, but that is the absolute top of any range I would consider acceptable.

So run 33-35, and measure in the morning, and don't overthink it.

My two bits...

Cheers,

Charlie

 

Yes, tire pressure changes with temperature. You are overcomplicating it. The manual says to check pressure with tires at ambient temperature.

 

+1 @cmt52663 comments. On my All4 S, I have the 17" rims, running 225/45r17 and use 35/32psi front/rear. I find the car to be very balanced and not at the expense of a rough ride. Although I am running the NM RSB and that certainly helps too. Those are the numbers suggested on my placard, BTW.

 

me too.