"The driver of a racing car is a component.... I changed gear so hard that I damaged my hand"
Juan Manuel Fangio, Formula One World Champion
Changing gear while driving a car is something we take for granted; but in the early days of motoring it was a much more delicate operation that required a lot of skill and practice. With the old straight-cut gears, the rotational speed of the gears had to be the same before they could be meshed together to power the wheels. However good a driver you were , the result was often a terrible grating noise.
Drivers had to use a complicated procedure known as double declutching. When changing up a gear the driver had to disengage the clutch, switch to neutral, and let the engine run down to a slower speed. It was necessary to re-engage the clutch for a moment, which slowed down the gears, allowing you to shift into the new higher gear. Changing down a gear was even worse. Once you had disengaged the clutch and shifted to neutral, you had to briefly engage the clutch again and give the accelerator pedal a boost, which would spin up the gears to a higher rotational speed, allowing you to then engage the higher, faster gear.
When Cadillac introduced synchromesh gears in 1929, it was a blessed relief for drivers without three feet. The concept was a simple one. The rotation of gear wheels still had to match up if you were going to engage one toothed wheel with another, but synchromesh did it for you. As the rotating wheels approach each other, protruding bronze rings and grooves on the gear wheels come into contact before the teeth. The contact friction quickly makes sure the wheels are spinning at the same rate before the teeth on the gears actually meet. By the 1950s synchromesh gears had become practically universal.
