Actually, it is not necesary to use spacer at front or rear. I am using factory Y214 staggered rims with 275/45/20 and 315/40/20 tires without any spacers. I runs perfect. I recently put my X to dealer for wheel alignment (KDS), now it is more perfect.

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--2004 E53 X5 4.8is - ECE version; right hand drive; Located in Hong Kong; ext. black sapphire metallic; int. leather black; adaptive dynamic bi-xenon headlights; 16:9 onboard monitor w/o navigation; 20" genuine BMW Y-spoke 214 wheels with Bridgestone Dueler H/P Sport tires; Int. rear view mirror w/ compass.