18" rims are a very nice upgrade! (steer clear of the 19" ones, from what I see, the rims are cheap, but the tires cost $$$$$$$ 20" would be the ultimate upgrade, but , that's a pricey option at best! I dream of a set of 20's! I run the larger iS brakes from a 4.6/4.8is X5, and the 18 inch wheels JUST clear the calipers!

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2003 X5 3.0i (02/2003) sport package, Sapphire black metallic / Black Dakota Sport seats. compass mirror retrofit, trailer hitch retrofit, Prodigy P2 trailer brake controller installed, PDC retrofit, Lumbar support retrofit. heated rear seats retrofitted. Running boards retrofitted and subwoofer install in progress. 4.8is Brakes installed front and back. Bluetooth TCU installed, Rear Fog lights installed. Retrofitted reclining rear seat backs.