[msej449]

I love my M235i Convertible, but as someone said, I regard it as more a great GT car than a sports car (in the sense of handling). And while reducing unsprung weight certainly may make a noticeable difference, I don't see that you can reduce the BMW's weight enough to turn it into something like a Caterham, or even a Lotus Elise.

The standard weight for an M235i (1455Kgs/3208lbs) is almost 2,000 pounds more than for my Lotus Elise 111S (806Kgs/1277lbs). While the BMW has a better power/weight ratio (224 vs 194 BHP/tonne) all that weight takes it toll on handling - which is fine by me: the MLite is a great all-rounder. I would never have taken the Elise on a long European roadtrip like I can the BMW.

So overall, yes, perhaps worth doing something about the wheels, but I'm not sure that bodywork and sprung weight trimming is going to get you a lot. Unless you alter the car so much that you get to a point where you'd be better off buying something designed from scratch to hit that spec' ....