I have 2, not 4, extra rims available to use as potential track wheels. I am wondering if I put a race-ish tire (i.e. Hankook V12) on those two rims and throw them in the rear, while still using pretty hard tires up front, will have a grip advantage over using all 4 harder tires? Will the hard/soft combo cause handling or predictability problems? Thanks!

 

I would think you'd introduce more understeer with that setup.