mercedes rims are made soft to prevent damage to suspension parts and vehicle from what dealer said, our 450 with 18" AT tires even being air born has never had a rim issue, we did switch to black rims when we bought it instead of silver ones but still are mercedes 18" rims, our 550 with 21" tires has had 3 rim straightenings and its never been off road, the ride is smoother and softer in the 450, the 550 is more responsive, can drive it like a race car but is not as soft and smooth, you can feel the bumps more which freaks us out hitting manholes sometimes knowing that probably just cost us another trip back to get the rims straighted again, the bigger the tires/rims the worse it seems to handle in rain from we notice living in florida, both have ads suspension. it will cost you more to own larger rims as we have learned. we drive the 450 more cause we worry to much about damaging the rims on the 550 but the 550 sure looks good having the 21' amg package compared to the 450. well thats our input, sacrifices are make either way. hope this helps