first off welcome and hope you enjoy the forum. the search function is phenomenal on this site and please read as much as you can, chances are your question might be active in another thread or answered over the course of the last 8 years or so that this site has been live.

If you are looking at 20" wheels, in staggered the OE sizes are 20x9.5 in the front, ET45 and 20x10.5 in the rear, ET30.

Some members have went with a square setup all around, however most of us desire the factory staggered look and setup that BMW equips the vehicles with from the factory.

There is a great wheel/tire thread in one of the other sections of the forum that showcases many pages of members rides and the different wheel/tire setups they have.

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards