Basically, OEM transmissions have Helical cut gears since they are quieter. The quietness is the main advantage but a major disadvantage is under high loads they produce large axial forces. These large axial forces also introduce the bearings and cases to forces that lead to failures.

Spur Straight cut gears allow us to improve the tooth profiles and eliminate the unwelcome forces that are related to helical gears. In turn results in a stronger overall gear. A disadvantage is that spur gears produce a whining sound similar to reverse gear. Having said that our current manufacturing technology allows us to produce quieter spur gears. Some users actually love the whine and complain our straight cut spur gears are not load enough.

The Picture below shows the TOP row with Straight Cut Spur Gears and the BOTTOM Row as Helical Cut Gears.