[dadzer]

Could be a typo but it is coming from the last page of the 2020 BMW pricing guide attached. It is shown as code 1XN for the 40i and 50i and is shown as code ZXN on the M50i. In both cases, the rear is shown as 21X10.0.

There is another 21" Y spoke, code 1XD, available on the 40i and 50i only, which shows as 21X10.5 but it doesn't have the M in front of it.

The M Y spoke code ZXN is the only 21" shown as available on the M50i.

Text copied from the guide:
21" M Y-spoke bi-color wheels, style 741M with performance run-flat
tires
Front: 21x9.5, 275/40 R21
Rear: 21x10.0, 315/35 R21
$950
Code: ZXN
Style: 741M ZXN will add 840 to the order

I thought this was strange as well. Can anyone verify if this is a typo?

If it is a typo, and the rear rim width is 10.5", since the tire spec states rim width for this tire is 9"-11" would I still be okay to go with 275/40 R21 all the way around?