assume they're from mark at bmautosport? got my old lm style wheels from him in 19s
he reports good things about nankangs - similar to what you say
to answer your q - the door sills should give you an idea but...
i was always told as bmws are RWD you should inflate the rear a tad more than the fronts (as the car rocks back when accelerating) so i kept my staggered 19s at 34 front and 36 rear but then i noticed wear on the inner aspect of the tyre (but that maybe the camber on the rears)
i suspect 32 front and 34 rear maybe better. try both and see how it feels?
love both the cars btw
