Re: 125cc engine!!!!!!!!
I have various stages of power. Motorized bike, 50cc scooter, 100cc motorcycle, and 800cc motorcycle. All have there proper places on the road. I HAVE ridden the 50cc scooter and the motor bike on some long trips.
Having said that I would never put anything bigger on a bicycle. But, some only have one bike and then the sky is the limit.
Or the frame and wheels. Or the cops.