Gears often play the important role of transferring rotational movement from one component to another, and doing so while allowing those parts to spin at different rates.
Teeth
When looking at a basic gear from its side, you'll notice a jagged, zig-zag, or otherwise repetitively uneven surface on the outside. The points that stick out are called "teeth", and the number of them on a single gear is important to note when comparing one gear to another.
If gear "A" has 20 teeth and gear "B" has 10, and these two gears are connected, gear A will spin half as fast as gear B. This is because the teeth interlock, and since it only takes 10 (half) of gear A's teeth to move all 10 of gear B's teeth, gear B spins twice every time gear A spins once.
Transmission Gears
The gears in a transmission are necessary for a vehicle which travels at a wide range of speeds (pretty much anything that isn't a basic lawn mower of go-kart) because the engine's range of safe operating speeds can't match the entire range of desired vehicle speeds.
Types of Gears
Not all gears are the standard flat, round, square-tooth design commonly seen in illustrations.
Spur Gears
Spur gears are typically what people think of when they think of a gear, and are usually the most easy type of gear to make due to a lack of complex shapes involved.
- Transmission Reverse Gear
- Flywheels & Flex Plates
- Starter Drive Gear
- Classic Manual Transmission Gears
Common Spur Gear Locations
Helical Gears
A gear with a helical cut design has teeth that aren't parallel to the shaft the gear is attached to. Helical gears are stronger than spur gears. They constanly have contact with each other which also makes them more quiet than a pair of spur gears.
- Manual Transmission Gears
- Gears Within Planetary Gear Sets
- Transfer Case Gears
Common Helical Gear Locations
Hypoid Gears
A set of hypoid gears is typically found in a differential. They are a derivative of the spiral and bevel gear designs. Hypoid gears need to be adjusted in two directions for proper contact.
Worm Gears
These gears are unique in the way they interact with other gears; they turn them, but standard gears can't turn worm gears. They don't have traditional "teeth", but instead have one long spiraling tooth.