Average top speed of the Ruckus is about 37mph - check out this site for further info on getting more out of it: http://www.battlescooter.com/6955/index.html If you know what you´re doing, you can use the parts on the Battlescooterstore (linked from that site) to boost the top speed.
The most you´re likely to get is 50mph - and that´s at a push!