Since you don't have a signature that includes any model/model year/build date info...I don't know if the info is in your owners manual or not...but this info is in the 2004-up owners manual...as well as on the tire pressure chart on the driver's door on all my BMWs.

As far as alternative tire sizes that aren't recommended by BMW...you can google a tire size calculator that can help you find an alternate size that keeps you within the correct specs for your wheel size & correct tire diameter/circumference. For instance, I chose an alternate winter tire size for my 06 X5...I went with 235/60/18 snow tires instead of the 255/55/18 tires listed on the BMW chart.

See example below from 06 owners manual...BMW lists the recommended tire sizes for the e53:

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• 2015 f06 650ix GC (Moonstone exterior/Cohiba brown Merino Leather interior)
• 2014 f15 X5 50i (Space Gray exterior/Mocha Nappa Leather interior)