Wheels generally fit onto the hub with lugbolts, BUT the part that hold the wheel perfectly centered is the 'centerbore' of the wheel that perfectly matches the locating part on the hub.

If the hub on the X6 is smaller than that on the X5, you would need to have the centerbore on the X6 wheel increased to match the centerbore size of the X5 hub.

You can buy some really crappy aftermarket wheels for your X...tirerack, etc, all have cheap, marginally made and heavy wheels for under $200 per wheel. The vendor will order the correct sizes... if you want your $65000 vehicle rolling on garbage.

BMW wheels are expensive, but they are high quality- do not assume it is just 'dealer' prices that make them high.

There is a reason why a set of HRE C20s cost $5k!

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