HYPOID SPIRAL BEVEL GEARS
THE hypoid gearing arrangement is similar to a spiral bevel gear set-up with the exception of the pinion, which doesn’t share the same axis as the ring gear – in a rear differential application it’s usually mounted lower.
The benefits of meshing the pinion gear on a lower axis is that more gear teeth are in mesh with the ring gear at any one time, meaning power from the engine is distributed on a greater area than bevel gearing. So, for the same size gearing, it’s able to transmit more power and torque. However, the gears slide over each other as they mesh, which creates friction. This friction costs power, so, while stronger, hypoid gearing isn’t as efficient.
There’s one other consideration with hypoid spiral bevel gearing: there are two sides to the gear, a drive side and a coast side, and the coast side is 30-40 per cent weaker than the drive. This is just one of the reasons not to perform a reverse snatch strap recovery.