[kriszty]

How to calculate the difference in % , and is the wheel size important or only the tyre size?

for example , i have a xdrive m240i , with default 7,5x18 and 8,x18 and 225/40 front and 245/35 rear.

if i buy new wheels 8x18 and 9x18 with the same tyre size (225/40 front and 245/35 rear) , is that good ?

thanks