Manufacturers usually indicate that the max weight on a scooter should 290-315 pounds. I'm about 245lbs and I ride just fine. The weight distribution is different two people so I wouldn't recommend it on anything smaller than a 170cc engine. (200cc)
I rented a 50cc scooter and rode all over town with my daughter on the back. She's 115 lb I'm 230 lb and we were flying everywhere without any issues. Moreover top speed was 30 mph plus with two people
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