In any gear pair, the member with fewer teeth. Because it turns faster, each pinion tooth meets the mating gear far more often, so the pinion usually sees more load cycles, more wear and higher bending stress than the gear and is often made harder or from better steel. The term also names the small gear in a rack and pinion and the driving gear in an automotive axle.
Pinion took all the pitting, it sees three times the cycles of the bull gear, so we're going a few points harder on the replacement.
Gear designers run the pinion a few points harder than the gear on purpose, so the two wear in together instead of the pinion eating itself.
Also heard as
- drive pinion
Related terms
Gear ratio
The number of teeth on the driven gear divided by those on the driver, setting speed reduction and torque gain.
Rack
A straight bar with gear teeth along it, which turns a pinion's rotation into straight-line travel.
Ring and pinion
Shop name for the hypoid final drive in a vehicle axle, named by its ratio, such as 3.73 or 4.10.
Bull gear
Shop name for the biggest gear in a drive train, usually the slow, heavy output gear.