True or False: Spur gears are generally more efficient than helical gears.

• A. True
• B. False
• C. Not sure
• D. It depends.

Answer: (A)

Spur gears are generally more efficient because their straight, parallel-to-axis teeth mesh with minimal sliding and no axial thrust. The contact between spur gears is predominantly perpendicular to the gear faces, which keeps friction losses in the tooth contact relatively low. Helical gears, with angled teeth, engage gradually and share load across more teeth, which improves smoothness and load capacity but introduces more sliding along the tooth surfaces and a thrust component along the gear axis. Those factors add extra losses and require thrust bearings, slightly reducing efficiency. In practice, both gear types are highly efficient when well lubricated; the difference is small, but spur gears tend to edge out Helical gears on efficiency due to the absence of axial thrust and reduced sliding in the contact.