you should be right 18s are sort of legal as you chassis comes with 16s standard for the sp20 am i not correct? or is it 15s.. eithr way 18 is max, well for me anyway, the ba v6 comes with 15s and the bloke at blowjobTmart said going from 15 stock 18 is largest or some thing.. if you do get 18s, 7.5 is a good width