Esmerelda's Home Page~ Z3ers.com From: Devon.Davis Spare Tire For the M roadster. I discovered that Kumho makes an ecsta tire that is 205/40/17. This tire on a 17" rim and inflated will fit in the trunk. I have driven with this spare on the front and back to test it out. Works great, drives a little odd since the tire is shorter than the standard tire, but it is a real tire so not limited to 50 miles at 55mph or anything like that.all material on these pages is copyrighted