Heh, every moped I've ever tried to pedal was like pedalling a regular bike uphill with flat tires towing someone on a sled... I think 15-20HP is a bit optimistic for the motor output too, I was thinking 150-250 cc bikes had about that.
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice