Which type of gear in final drives allows for a larger speed reduction?

Worm gears are particularly effective at achieving significant speed reductions due to their unique design. In a worm gear setup, a cylindrical worm (the gear with a screw-like shape) interacts with a gear that has teeth designed to mesh with the worm. This arrangement allows for a high gear reduction ratio because the worm can turn the gear with fewer rotations, which significantly reduces the output speed.

Additionally, worms offer the advantage of self-locking properties, meaning they can prevent any motion of the driven gear if the input is stopped, a characteristic very valuable in mechanical systems where holding a load in place is necessary. The steep angle of the worm's thread allows for this dramatic speed reduction effectively, making them a crucial component in applications requiring substantial torque and reduced rotational speed.

In comparison, spur gears generally offer low to moderate reductions, bevel gears are used for directional changes and can also provide some reduction but not as effectively as worm gears in high speed reduction scenarios, and planetary gears are more suited for delivering high torque with multiple speeds rather than a single large reduction. Thus, the worm gear stands out in its capability to provide larger speed reductions effectively.