[BMWOO7]

I was going to say the same thing, try Tire Rack.

What I like to do is find the tire your looking for, then go to the 'specs' tab or section and see what the diameter is or the 'revs per mile'.

I think factory standard, at least from what I've seen is a difference of like 7-10 revs per mile and about .3"-.5" difference in outer diameter (OD).

So you'll usually see like a 35 series up front and then a 30 series in the rear.

I'm not that familiar with tires that large (22") so I don't know that I could help ya more than that.

The only other thing I'd do is contact several of these tire and wheel places that sell these 22" or 24" wheels and see what they recommend for something like this.

I'm guessing that your main concern is ensuring that the XDrive doesn't get messed up and still operates properly. With that said, you could try BMW to see if they could tell you what the max difference in tire size can/should be, but I don't know if they'd know past the factory OEM wheels and tires.

In either case, please post back with pictures and what you end up finding out!