I am trying to choose between two tire sizes for Autocrossing use only. One , my current size is 245/45-17 which give me a wider track so more rubber to the ground for adhesion and braking. My other choice is to go 245/40-17 which lowers my sidewall thus less flex in corners , plus less overall diameter for quicker acceleration. I am thinking that sidewall size is the more important factor , am I right?