from the thread thejeremyman9 linked, my post here,
https://f30.bimmerpost.com/forums/sh...23&postcount=2, suggests you increase the front tire size from 225/40/19 to 245/35/19, rear stays the same. 245/35/19 front, 255/35/19 rear, approaches square and will reduce understeer significantly. i suggest you get the MPS4S in XL(extra load). the higher load indexed stiffer sidewall will provide sharper turn in and less deformation during high load cornering during track use. the daily ride will be a little firmer, though.