One’s teeth of a helical gear are set at an angle (relative to axis of the gear) and take the form of a helix. This allows the teeth to mesh gradually, starting as point contact and developing into series get in touch with as engagement progresses. Probably the most noticeable benefits of helical gears over spur gears can be much less noise, especially at moderate- to high-speeds. Also, with helical gears, multiple teeth are always in mesh, this means less load on every individual tooth. This outcomes in a smoother transition of forces in one tooth to another, so that vibrations, shock loads, and wear are reduced.

However the inclined angle of one’s teeth also causes sliding contact between the teeth, which creates axial forces and heat, decreasing efficiency. These axial forces enjoy a significant part in bearing selection for helical gears. Because the gear rack bearings have to endure both radial and axial forces, helical gears need thrust or roller bearings, which are typically larger (and more costly) than the simple bearings used in combination with spur gears. The axial forces vary compared to the magnitude of the tangent of the helix angle. Although larger helix angles offer higher speed and smoother movement, the helix angle is typically limited to 45 degrees because of the production of axial forces.