Ahh.

The X5 is rear drive bias, which means the rear is doing the majority of the work. More rubber in the back gives better traction and better handling in a curve. That is why some models come staggered (i.e. the performance variants for sure).

A definitive list? Not sure. I'm sure some of the regs on here can come up with something.

BTW: a 255/50 vs 255/55 is simply a change in overall diameter and sidewall height via the aspect ratio. The tire is no wider tread wise If you ran 255/55/19's on your X5 it would sit a little higher in the front.

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