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There's a discussion remarkably similar to this under "need new tires". There can be different reasons for different rates front/rear. Staggered sizes is one - the MSport x1 has these - bigger tires in the rear (at least ours does). My S2000 is the same & specs different pressures. Also generally speaking a harder tire will usually have better traction and you want that with the driving wheels. Can't really speak to Ow40x1; maybe there's an upper limit, maybe it's the driving style - that car is a rear drive & with that when the car is balanced & has power sometimes it doesn't take much to make it step out (again the S2k is same)
The A4 mentioned by halfmoonclip makes sense - isn't it mainly front drive & a little nose heavy ? I had an Integra GSR that also specd higher in front. The standard Integra was specd even but the GSR was specd differently (it also had more power & was more tightly sprung for those who aren't familiar with the GSR)
The main thing is the cars were designed a certain way & tire pressures dialed in by the engineers. BMW has the rep for handling - I'm sure they're going to pay attention to that. They're saying "this is how it should be" & the cars drive very well; I would trust their specs. There's also liability if they spec wrong (Ford Explorers & Firestone).
A note on varying the pressure more than a little bit - I've noticed that uneven wear-especially due to incorrect inflation- is intensified in lower profile tires.
Just my thoughts . . .
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