This was a toy with a zip cord you pulled that went into a gear-mesh behind the wheel. When you pulled it, you placed it on the ground and it zipped off down the road! Toy cars which when a zipper cord was pulled, would race accross the ground at high speeds. Little cars that contained a flywheel in the center. You fed in what looks like today's zip cord, then you yanked it out hard and turned the car loose. They were pretty fast; mine usually zoomed under the sofa or some other inconvenient spot. Stange-looking cars with a single central gyroscopic wheel that you would rev up using a plastic "rip cord". There was also a Demolition Derby variety that was a lot of fun. Cars with a large wheel in the center that you fed a plastic "rip cord" through and pulled to get the large wheel going. Also had SST smash up derby that came with two ramps and two SST cars with pieces that flew off when they hit something. Little cars with a large rubber wheel in the center. You inserted a long toothed plastic strip into the gears by the wheel, and pulling it out spun the wheel so the car would go. Came in a bunch of different types, including "Demolition Derby" where two of them were designed to shed parts when they crashed together.