I was thinking/wondering if a slower rotating, taller tire might have more traction. I have never seen nascar run different sizes, I have seen sprints though. I just figure why be normal plus I like to steer it, I have rode 4wd atv's for a long time with large mud tires, plus none of my farm trucks have power steering so forcing a machine to turn is almost second nature now. We are in the process of building a Mod-X with 13's up front so I will be riding it soon to feel what it is like.