The chopper does not really have an exact chopper motor. Since motorcycles are weak, you can easily fall off them, and not even damage the car you hit much. Along with the Ducati 999, a good way to steal one is to crash into someone's bike hard (if they're driving it). They'll fall off. This is a good time to steal it. Some choppers along with the Ducati 999 appear parked, but both of them are quite rare. Once driving this motorcycle, other people driving the Harley Davidson V-Rod and Harley Davidson V-Rods themselves will appear.
It is slower than the Ducati 999 sports bike, but is still fast. Like the sports bike, you can easily fall off the chopper if you crash too hard.