One disadvantage of helical gears is the generation of which effect?

• A. Noise
• B. Pitting
• C. Side thrust
• D. Low efficiency

Answer: (C)

Helical gears generate axial thrust because their teeth are angled, so as they mesh the contact force has a component along the gear axis. This axial component, or side thrust, presses the gear and shaft in the direction of the axis and is the main drawback of using helical gears. It increases loading on bearings in the axial direction and can cause misalignment or premature wear unless you use thrust bearings or countermeasures like pairing gears with opposite helix angles to cancel the thrust.

This is why side thrust is the correct point: it’s the unavoidable axial load that accompanies the inclined tooth contact. The other issues listed—noise, pitting, and low efficiency—aren’t fundamental disadvantages specific to the axial thrust in the same way. Helical gears are typically quieter than spur gears and pitting relates to surface wear, while efficiency losses from sliding exist but aren’t the defining drawback in the context of this question.