I am finally ready to try R compounds after 3 years of autocrossing and a few track days on street tires. I have two sets of 18" wheels; the stock 8 inchers and some BBS forged purty ones, 8.5" front, 9.5" rear. I still plan on running some distant events on street tires, namely track events. (Seeing as another investment is required to carry a set of racing tires out of town)
So which wheels should I use for the R compounds, and what size tires should I get? If I put the race rubber on the stockers, I'm running heavy wheels for racing. Supposedly you can put 285's on them (poor tire jockey!) Or I could run 245's all around and save money/trouble. This would allow me to continue to run wide tires on the street/track, and use the wheels I spent so much on for daily driving.
Conversely, I could mount those R comp 285's on my light BBS wheels. For vanity's sake, my car mostly gets photographed at autocross events, not in my office parking lot, and everybody appreciates good wheels at such events. This would leave me with the stock wheels and maybe 255's all around for street tires. I would be more inclined to drift on the stock wheels, which goes along with my idea of using street tires for distant track events. Plus, the car attracts less negative attention on the street with stock wheels. I'm married, so I don't care what the ladies think.

I guess I need to know if it is worth the money to buy 285's over 245's for R compound tires, and does the weight/narrowness of the stock wheels make much difference?

BTW, I am N/A, and will be buying big brakes this year, both important factors)

 

It depends upon what you want to do -- look good or be competitive.

Once you go away from the stock size of the wheels, you're into the "big" (BSP) or "bigger" (SM2) bucks classes. Locally that may not be a problem...

 

I have 3.91 final drive gears, putting me in SM2. I decided at some point not to let SCCA rules get in the way of building the car the way I want it. My driving in the "street tires" category is making my friend in SM2 nervous
Basically all my friends told me to get some real tires. I am wondering if there is a lot of difference between 245's and 285's on an autocross course.

 

hellll yes there is. you want as much grip as possible... don't limit yourself to 285s if you can go bigger.

 

Yes there is, but is it enough of a difference to be significant at your (or my) skill level? Put Tom Berry, Rita Wilsey, Gary Thomason, Ken Motonishi, Bob Tunnell, etc. in your (or my) car on 245s and then you get to drive it with 285s. Who do you think will be faster on course?

 

What if Chuck Norris was driving my car on 225's?

Since I'm not competing on a national or even regional level, I'm more concerned about how much benefit I will get from the experience. When I start comparing myself with others instead of focusing on self improvement, things go downhill.

 

He would kick everyone's ***, but once he farted in your seat the car would be undriveable.

Putting 285s on 8" wide wheels is a ***** and for your use its not worth the trouble, IMHO. I would keep the 8" wide street tires for street use and autocross the BBS wheels. Unfortunately with the widths you have you'll probably have to go with 245s front and 285s rear which will give you a little push. You can try a set of 245s or 285s all around but one pair will not be optimal.

I tend to have more "fun" when I'm running a car with "skinny" tires. It isn't the fastest but you get to spend more time at the tire's limit working on feeling out slip angles and keeping the car balanced on the top of the tire's traction curve.

 

We're running 285's on the OEM Track wheels (8" F, 8.5" R) w/o any problem. The tire shop we use was able to mount them very easily. You will have to run a small spacer (.25" is SCCA Stock class legal) on the front so the tire will not rub the suspension arm. Put as much tire on the car as possible, they work well!
If you wan to run bigger, 18x11 will work great w/ 315s. Have CCW build you a set of wheels...