One’s teeth of a helical gear are set at an angle (relative to axis of the gear) and take the shape of a helix. This enables the teeth to mesh gradually, starting as point contact and developing into range contact as engagement progresses. One of the most noticeable benefits of helical gears over spur gears can be less noise, especially at moderate- to high-speeds. Also, with helical gears, multiple the teeth are usually in mesh, this means less load on every individual tooth. This results in a smoother gear rack changeover of forces from one tooth to the next, so that vibrations, shock loads, and wear are reduced.
But the inclined angle of the teeth also causes sliding get in touch with between the teeth, which creates axial forces and heat, decreasing performance. These axial forces enjoy a significant role in bearing selection for helical 
gears. Because the bearings have to withstand both radial and axial forces, helical gears need thrust or roller bearings, which are usually larger (and more costly) than the simple bearings used with spur gears. The axial forces vary compared to the magnitude of the tangent of the helix angle. Although bigger helix angles provide higher swiftness and smoother motion, the helix position is typically limited by 45 degrees due to the creation of axial forces.