Generally speaking if it wobbles at 60+ and not below its tires, thats on a car, truck, scooter, motorcycle, or mattel hot wheel.
Honestly 250cc is the bare minimum for highway, I have many bikes and I no longer ride anything below 600cc on the highway. With that said though I dont believe you shouldnt be on the highway either. I use to ride my heavily modified ke100s for 45 miles both ways on highway 44 to 270 to 30 here locally on the regular to one of my properties, it was going on 11 years strong. If a 1979 rotary valve 108cc AC enduro can do it safely a new 250cc water cooled scooter sure can. Although, I no longer ride my small bikes due to being blown over a whole lane on my klr250 when a 18 wheeler blew past me doing 80 MPH+ on a 60 MPH road, (idiots cant do the speed limit). After that I vowed to never ride anything under powered. You need that reserve power to pull you out of a head wind.
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