Spur gears are the most typical type of gears. They possess straight teeth, and so are installed on parallel shafts. Occasionally, many spur gears are used at once to create very large gear reductions.
Spur gears are used in many products that you can see all over HowStuffWorks, like the electric screwdriver, dance monster, oscillating sprinkler, windup alarm clock, washing machine and Oil less Air Compressors clothes dryer. But you won’t find many in your car.
This is because the spur gear could be really loud. Each time a equipment tooth engages a tooth on the additional gear, the teeth collide, and this impact makes a sound. It also increases the stress on the gear teeth.
To lessen the noise and tension in the gears, most of the gears in your car are helical.