Spur gears are the most typical kind of gears. They have straight teeth, and are installed on parallel shafts. Sometimes, many spur gears are utilized simultaneously to create very large gear reductions.
Spur gears are found in many gadgets that you can see around HowStuffWorks, like the electric greenhouse reducer powered screwdriver, dancing monster, oscillating sprinkler, windup alarm clock, washer and clothes dryer. But you won’t discover many in your vehicle.
This is because the spur gear can be really loud. Whenever a gear tooth engages a tooth on the additional gear, the teeth collide, which impact makes 
a sound. It also increases the pressure on the gear teeth.
To reduce the noise and tension in the gears, most of the gears in your vehicle are helical.