The front axle is 12mm in diameter on the Grand Vista 250.
When I took the scooter in for new tires, the mechanic could not balance the front wheel
because his wheel balancer had a shaft diameter larger than 1/2".
So I finally found a tire shop that had a balancer with a 12mm shaft and got the job done.
Might want to check with your garage before getting new tires to see if they can balance them.
Avon tires.
scoot safely,