Tether cars are model cars with gas control-line engines. They have no radio control. They are “controlled” by a wire connected to the car at mid point and to a pole at the center of a circle at the other end. They cars run around the circular track until their control-line engines run out of fuel. In competition, the purpose is to run the car as fast a possible.
Tether cars still exist today in the form of streamlined land speed vehicles and use modern nitro fuel engines. There are several tracks in the USA, one of which is on Long Island, New York.
There is another form of gas powered tether cars that run along a tether-cord laid out on a scale drag strip. The car has a groove underneath the chassis through which the line passes. The Cox Manufacturing Company made and sold these in many toy stores. The current Cox Manufacturing successor, Estes Rockets, manufactures a similar rocket-powered toy car.