I have 18" rims with standard 235/60R18 tires (tyres in my part of the world!!) on my XC60 T6

The rolling circumference of a 255/55R18 tire differs less than 1% to that of the standard tire so it is potentially a good replacement - however, it is much wider and may cause problems with scuffing on the suspension on bodywork. Also, these tires are quite noticeably heavier so the unsprung mass increases.

So my question - does anybody have experience with this alternative tire size? Results?