Autocross/Road Course driving on 15" wheels. What's your experience?

I've done two time attack events in my Duster with 15" Rallyes and fat tires (215/65-15 front and 275/60-15 rear) and it sucks lol. On one lap I tried airing down my fronts from 40 to 35 psi hoping for a bit more grip but all that happened was the sidewalls started rolling under the wheels and my grip got worse.

Over the winter I plan to go to 18" wheels and some legit performance 40 or 45 aspect ratio all- seasons. I'll see how those do at the next track event I can get to and if I need more grip I'll get another set of wheels with track- only tires.