This is my reason for the 10.5 tire rule. From the outside the cars should look close to the way the were in the early to mid-60's. I know most run modern wheels, wheelie bars, etc. but the smaller tire lends itself to a more nostalgic apperance in my opinion. The smaller tire also adds another element to the challenge of getting a fast car down the track.

To be honest I'd like to keep it stock style suspension and real 10.5s but I know that would eliminate many current cars. 10.5w's are a plenty big tire.