For my '15 MCS the factory specifies 38/35 psi for the original runflat tires. But, not caring for runflat tires, I promptly switched to some regular Michelin Pilot Sports. I have run the Michelins at the same 38/35, but they seem harder that I expected.

I wonder what the Mini factory would have specified if they weren't installing runflat tires. A little softer maybe?

 

Pilot Sports you say?

Pilot Sport 3
Pilot Sport PS2
Pilot Sport PS2 ZP
Pilot Sport A/S 3 (W- or Y-Speed Rated)
Pilot Sport A/S 3+ (W- or Y-Speed Rated)
Pilot Sport A/S Plus ZP
Pilot Sport A/S 3 (H- or V-Speed Rated)
Pilot Sport A/S Plus N-Spec
Pilot Sport Cup
Pilot Sport Cup 2
Pilot Sport Cup 2 ZP
Pilot Sport Cup ZP
Pilot Sport Cup+ / N-Spec

It is a general recommendation that can be varied by a few pounds +/- without ill effect on tread wear. Some tires want more; some want less. Same with people.

 

If you want to get all kinds of engineery/technical, you have to look at the load rating for the original tire, as well as the max inflation. The max load rating is at max inflation, and there is some sort of non-linear load rating to inflation adjustment. If the load rating is the same and the maximum pressure is the same, you should run the same pressures. If either changes, you should change pressures to achieve the same ratio.

Since you aren't designing an OEM system though with 12 engineers, just keep the same pressures you were running before - it's totally fine.

 

Here you go, simple to figure if you are a well versed tire nerd, http://bndtechsource.ucoz.com/index/...alculator/0-20 , I can't figure it out.

 

What pressure did the tire installer set the tires at?

I keep mine at 35 psi all around. That's what the installers (Discount Tire) and the MINI dealership set them at whenever they do something with the tires.

I have non-run flats.

 

38/35 cold.

 

I'm running my Conti Extreme DW's at 38F/35R. My Conti's still ride better than the Hankooks at those pressures.

The 35psi all around seems to be the default pressures many places use (rather than reading the sticker in the door). Likely no harm doing that, just if you lose a bit of front tire pressure over time, it will trigger the low pressure indicator sooner than running w/ 38 psi.......

 

The answer is in your manual for JCW:
42 39
205/45 R 17 88 Y XL Std
205/45 R 17 88 V M +S XL A/S RSC
205/45 R 17 88 V M +S XL RSC

 

I ran the PSS's-215/45's and set them at 35 cold.

 

I would not recommend going less than 35.

 

I wonder what the tire pressures the JCW team run? I'm interested in maximum traction.

 

I wouldn't take the tire installers pressures as a recommendation. As far as I can tell, they always set every tire to 35psi, regardless of whether the door plate says 32 or 38 or 40.

 

Doesn't matter -- it won't apply unless you are driving on a track, and even then, their settings only apply to you if you are on the same track with the same tires and in similar weather conditions.

Rule of thumb on the track: check your tires after each session. If the difference is small, bleed down the highest tire(s) to match the pressure of the lowest. If the difference is large (say, 38 up front and 32 out back), bring them both to a mid-point (say, 35 in this example). The point of this is to keep the tires' temperatures, and thus traction, all the same in your next session. Check and adjust after each session. Which tires run hottest and coolest will depend upon the track and your driving style.

Generally, when testing to find the right pressures, you'll want to start out (tires cold) about 5psi lower than normal pressure. This allows the tires to flex more to heat up quickly. As they heat up during the lap, their pressures will increase (about 1 psi per 10 degrees Farenheit). You let air out of the highest pressure tires to bring them all into equilibrium.

You'll also want to take notes on how the tire feels in terms of grip. If they feel slippery, your pressure is too high. If they feel spongy and wobbly, it's too low.

I've simplified and condensed a bit here. If you'd like to go a bit deeper on it, here's a great article:

http://www.turnfast.com/tech_handling/handling_pressure