Simple answer is that there has to be rules. Box stock has to mean box stock. Or you get people, even in friendly competition, looking for loopholes.

You will get a range of opinions about the aero effects on these cars. While I see it watching the Mod class run at big track. I ran my basically box stock car with a partial broken rear spoiler with no effect. Big track or mini96.

I haven’t tried running different sized wheels. I could see them altering the drive ratio. With real world cars, I’ve seen cars change with altering wheel size. In these cases it’s usually going to larger wheels.