[915Max]

Here's my problem:
Due to the fact that this lady in a van got into my lane, cut me off, and didnt speed up, I have to get some new tires.... my tires ended up getting a flat spot because my car just slid.
Anyways, i'm going to start getting into autoX and road courses this coming year but i'm faced with a tough decision. I was thinking of buying some good quality tires for my 18's to do the track racing, but then I thought of getting some 17's with some nice tires for the track, and some cheap tires for my 18's (daily driving). I really dont want to spend too much cash and I really like the look of the 18's on the car.

My question is: How well would my 18x7.5 rims do on a road course using a 235/40/18? Would I benefit more dropping down to a 17x7 or 17x7.5 rim and using a 225/45/17 tire!?
I currently have 235/40/18 Nitto555's tires, and when I first got them, I took a tight, underpass, turnaround that is two lanes wide going about 65, and the car handled perfectly... the car didnt slide or feel like it was gonna lose control.
Can you experts please help me out.