A fair amount depends on the pocket bike, too. One of the Chinese rip-offs (CAG) will go a lot slower than a racing quality PB like a Polini or Blata. I have one of each and the Polini will hit 40 - 45 mph, while the CAG is good for 20 - 25 mph or so.
I agree that you can have more fun with a 50cc, though. A lot more guys 'borrow' them from their kids and take the racing on local go-kart tracks. It's something to do when the snow flies for us Northerners.
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