I have Sorex 24s for the front and 20's for the rear with HPI Red inserts. Our track is medium grip carpet and this is a combo I've tried and really like.
Why different front from rear? When running rubber, use the same for both front and rear. The marking on the tires are based on temperature, so I do believe 32's would do you good. In Europe, we can tractionroll with those tires, so I really do wonder why all americans always choose 20 and 24 for high grip carpets.
Many people say tires are the most important aspect of a good setup. Nowadays, that's basically wrong. All tires(CS, Sorex, Powers, RP and so on) are very good nowadays, and you can't really go too wrong, too far off pace. The biggest difference between the tires is wear and cornerspeed, but most of them feel comfortable on the track.
So, the most important aspect of running fast, is inserts. Having the right inserts for the right tires is extremely important, and molded inserts are no good for modified carpet racing. As mentioned before in this thread, the JB foams is the only choice! It is so much faster on carpet than molded inserts, you guys won't believe it until you try. Ok, so molded inserts might feel great, but I assure you, your laptimes will improve with JB.
Period.
I bought a set of Proline Speed 10/24mm rims (I'm not a dish wheel fan, sorry), but it seems that there's a little play between the tires and the rims. I put them on the stock Xray rims and they're snug. I'm assuming that the Xrays are Inch-Up rims. I don't want to use them because I hear from a few veteran rubber runners, that they crack more easily than others.
What?? The Xray rims are some of the most solid wheels around, If you crack one, I can buy a new one for you, 'cause that deserves a prize!
I heard from some other forum that guys in the UK flip the tires inside/out and put a strip of glass tape (think it's that fiber tape) and then flip them back. This keep the tires from expanding during high RPMs. They also say to use Inch-Up wheels which does seem to let the tires mount more evenly and will reduce sidewall flex, I think.
Considering that all racing tires these days are belted, that is nothing you need to think of.
Does it make a difference if you use 26mm vs 24mm rims?
If you run 26mm tires, run 26mm rims. If you run 24mm tires, run 24mm rims...