Well it really depends on what size of dirt bike you get. For example: if you get a 50cc bike it will mabe go 20mph, but if you get a 450 it could go from 50 to 60 mph. so to get a definite answer go to your dirt bike companies website, and look at the bikes facts.
Dirt bike speed varies according to its engine capacity like 400cc has an average speed of 87 mph while 450cc go up to 90mph.
60-65 tops with stock gearing, a motocross bike is not about top speed but how quick and how well it handles.
size of the engine
yes, dirt bikes are motorized
I could see the top 5 or 10 (excellent article on the 10 used bikes still capable of wining with in the Jan 09 Dirt Bike mag) but who cares about the top 100 bikes!
dirt bikes
Everybody that races dirt bikes "started" racing dirt bikes at some point.
dirt bikes in the past had less gears and power then dirt bikes have today
The two main types of dirt bikes are motocross and trail bikes. Yamaha, Kawasaki, and Honda all make these types of dirt bikes.
no dirt bikes arn't illegal
no there not dirt bike is better
25-27-mph standard top speed for a mini dirt bike
dirt-biking is for dirt-bikes it can be either stunt or mud riding