I bought a collapsable spare off a 2002 SLK 320 from a yard in Calif. about 4 yrs. ago & it works the way it should on our Xfires. I've had it on both front & rear axels & there is complete clearance of the calipers & all other objects. My spare was never used & it came from a totaled 320. Got it off e-bay for $100. plus $20. shpg. It's quite a view to see this tire expand with air & retract back to donut size when it's job is done. I measured the size from the ctr of the wheel tread straight across to the ctr of the tread on the opposite side when collapsed & ordered a black spare tire cover off e-bay for a little travel trailer tire & it blends nicely in my gray colored trunk area. To me it's worth knowing it's there. Hope I don't get into too serious of a front end smash-up!!!!!!