I was a huge Evel Knievel fan when I was a kid, which was right in the middle of his heyday as a daredevil. I used to tune in on ABC's Wide World of Sports and watch all of his jumps. I had the toys, too (seen at right)! My brother and I would use the ramps from his SSP Smash-Up Derby set (below) and Evel would jump over the cars, which we lay side-to-side between the ramps. It was fun sitting on your knees, revving up the motorcycle.
Basically, the rear wheel of the motorcycle rested along a toothed gear that you rotated using the handle on the plastic base. The rear wheel had a medium-resistance gyro in it, so the faster you got it going, the more stability the motorcycle had when you released it. This is also what allowed the bendy action figure to ride the bike through flips and loops and still land upright and keep riding.
After Evel's Snake River Canyon fiasco, my dad bought me the Skycycle toy for Christmas. It was a cool-looking toy, but the skycycle was the worst-performing Evel Knievel vehicle, ever...which come to think about it, was historically accurate.