Hi Tom,
Sorry for going OT, but...
My car is a 2010, 135i 6sp manual. My door jam sticker says this:
36/39 psi for 18" summers (under 100 mph speeds!)
38/42 psi for 18 summers (OVER 100 mph speeds!!)
I guess since my US spec car was delivered in Germany I get this added yellow decall!
I also got the 155 mph speed limiter. Although I have not tested that out - yet! My winters are only good for 130 mph!
In my owners manual I found specs for my 17 winter tire pressures:
33/36 psi winter (under 100 mph speeds!)
38/42 psi winter (over 100 mph speeds!)
It also lists the pressures for 18" winters
215/40R18 36 psi (38 psi over 100 mph)
245/35R18 39 psi (42 psi over 100 mph)
I don't really know why anyone would go with 18 inch winters - you want the skinniest and tallest tires for winter performance anyway. Only thing I can think of is for people who don't want to buy a 2nd set of wheels for winter duty.
Like I said in my original post: I run 34 & 39 psi in my 17's winter setup. I find it the best compromise. but run what works best for you.
bye,
David