Zenith The of variable drives

The early years of motorcycles, or motor bicycles as they were known back then, always seems to amaze me. A recent brush with a Zenith Gradua had me fascinated and led me to research more about this marvel. This is a snapshot of what I found.

Let’s begin at a period from the year 1900. The internal (also referred to back then as the ‘infernal’) combustion engine was very basic with a very narrow rev range. It was a matter of tweaking the ignition advance, air and throttle control to find the sweet spot and keeping it there. These days we have a wide range of usable RPM and we use the throttle liberally to control speed. Given that engines were best left at their optimum RPM, the transmission system was developed to adjust the ground speed of the motor bicycle to suit various engine loads. Initially these transmissions were simply direct drive but as years went on the virtues of variable gearing evolved. A summary of this evolution leads us to a period when the Zenith Gradua was the industry benchmark.

Direct Drive Direct drive transmission used a belt, chain or shaft to directly connect the engine to the drive wheel. The decompression lever allowed the engine to turn over with minimal friction, allowing the machine to be pushed around with the engine stopped. A special start technique was also necessary. The rider would activate the decompression lever to push the motorcycle to an appropriate speed, jump onto the seat and then release the lever to allow the engine to start and off they went. Early machines retained the pedal drive of the bicycle so that the rider could alternatively pedal instead of running to start. These pedals