Whats wrong with oversteer?
doesnt have to be 20mm it is OEM, but on my LMGt4 i had 225 on the front 255 on the rear no issue at all, ive also ran 245 front and 275 rear with no issue (only issue caused was when moving to a lower profile on the 245), Traction control more works on rolling radius than tyre width as it works but working the travel speed of each wheel out then it notices one wheel spinning out of sequence with the other it will apply brakes etc to bring them all in line again.
I could have a 215 up front and a 315 in the rear as long as the rolling radius is in line with each other via the profiles Traction control wont have an issue