Originally Posted by HIRISC

You're right on!

• Y Spoke, style 335 - from the optional 'Sport Activity Package' are 4 x 255/50/19 run flat all season on 19 x 9" wheels.
• However, V Spoke - 223M - from the optional 'M Sport Package are (f) 255/50/19 (run flat performance tires) and (rear) 285/45/19" on 19 x 9 and 19 x 10" wheels

Not a giant difference, but 285mm rears are still > 11" wide.

Both 20" wheel options provide 275/40/20 and 315/35/20 run flat performance tires on 20 x 10" and 20 x 11" wheels, respectively.

Standard and optional equipment list from BMWUSA:



Here are the 19" style 223M on the 50i M sport pack X5 I drove last Saturday. I'm going with these as comfort > style at this point in time.






I tweaked the contrast on this pic so you could see 'the width' of the silver X5 with 19"s. Not ///M (my white car), but the way that BMW spaces them 'out', they look fine.