i think its all about surface area, as a larger wheel has a higher surface area = more power.
Also a smaller wheel has to turn faster putting more strain on the engine.
But that is all a guess
larger surface area = more power???
so i can stick a 12J wheel with something stupid like 265 tyre on, and i have "more power"
more like i'd have less at that redicilous size, as you need to overcome more friction
and smaller wheel doesn't put more strain, a bigger one does, did you watch top gear where they went to south america, did you see what happened when they put massive wheels on? they act as gearing, so they had to rev higher just to pull off, then it messed up their engines!
Zero, what tyres you running on the RM's? and what width are they?