He's talking about the little 80cc dirt bikes and pocket bikes and scooters that the guys at the drags use to pull their hopped up cars back from the end of the track. Some of them can't drive themselves back because they would overheat (top fuel dragsters funny cars ect.) since they have no cooling passages a lot of times. The engine only has to run for a 1/4 mile then its done. The bikes don't get over 20mph or so and they have little doughnut tires.