A tip I picked up from another forum and checked myself. I have the same size tyres on the C270 and the front of my 968 - namely 205 55 R16. Flaken FK452's on the C270, Pirelli P6000's on the 968. Falkens are only slightly wider than the rim, Pirellis are a good 1/2" wider - thus rim has some protection from accidental kerbing. Goodyear Eagle F1's on the back of the 968 are the same, as apparently are Michelins and Toyo T1R's. OK, we don't aim to kerb the rims, but it happens - and some tyres give your rims more protection than others.