The unit didn't start to bounce until the rear tire was changed. Where does that lead you???? What could they touch replacing the rear tire? Remember, if it was the chain, why didn't it bounce with the old tire on?
Some things to double check?
1. Bad tire -
2. Balance issue with rear tire
3. Chain too tight
4. Bad/binding Cush Drive rubbers - Remember, the wheel is usually balanced without the cush drive and sprocket installed.
