255 on rears

[showtime1]

need a set of rears soon thinking of running 255/45 or 40 as the avon zz3 are quite narrow compared to other tyres the same size. would this be ok still running the 225 at the fronts.

[Ekona]

I can assure you a ZZ3 in 245 will be the same width as a T1R in 245 Stick with the stock width and profile unless you have cause to change them, and then you change them in relation to each other (i.e. you go wider at the front, you go wider at the back).