The major difference between the larger scoots, and the 50cc's is the frame. the material is stronger, there are more gussets, and it is overall stronger. The 50's are made to be a run to the store type scoot, and the 150's+ are made to be road worthy. Just a basic idea! Tire size is the most important aspect in handling. While not wanting to get all engineering type here... A 10" tire going 50mph is turning x=rpm's A 10' tire going 50mph is turning less than x. So stability of the tire is = to the rpm's it is turning. I understand the risk of passing the safe handling limits of any given tire size, and attempt to compensate for the negative handling w/ all the years of experience I have riding. A perfect example is 4 of the exact same scoots w/ 4 different riders. One rider will always come out on top no matter which scoot he rides. The handling of the tire size is 1 factor, and the other is the strength of the frame. That is the limiting factor on tuning my 50cc. I could easily add another 5-6hp, and 10mph top end speed, but even if I brace the frame there is not enough margin for safety. Sooooo For now I enjoy just knowing my scoot is as fast as it can safely be, and I ride it in that fashion. Now just so I don't sound like a callous jacka$$ tearing about... I live in a very sparsely populated area. Our roads are primarily flat, and straight. If I lived anywhere else my riding style would be GREATLY modified. I might even give up the 50cc for a 400cc enduro type motorcycle. Then it starts all over again. 125mph 400cc.