If you work with motorcycles or perform your own transmission fluid changes, you will have been introduced to gear oil and specifically hypoid oil at some point in your mechanical learning. That said, most people have no idea what hypoid oil is, much less what it is used for.
What is Hypoid?
The term "hypoid" has more to do with the construction of engine gears than it does with oil. Early automotive engineering involved gears that meshed with each other straight on. When you think of gears, this flat face-to-face gear teeth approach is what we learnt as kids in cartoons and marketing images of big machinery. However, automotive design soon figured out this gear approach was inefficient and also very loud when running. Thus, the "hypoid" design was invented which basically has two gears shaped like Christmas trees mesh with each other at 90 degree angles or similar. The hypoid approach reduced gear-meshing noise and it allowed greater torque pressure for stronger drive. The design was so successful every car and vehicle today uses it as a standard transmission design. Due to the higher pressure on gears as a result, the lubrication needed has to include ingredients to provide more protection for the gears. This special gear oil is designed not to deconstruct under higher pressure.
Gear Oil in General
Gearbox oil or fluid is used in all sorts of vehicles. It provides lubrication in transmissions, wheel axle differentials and other parts of machinery. The viscosity level on gear oil is much higher than normal engine oil to make sure gears don't grind against each other. Over time, if not cleaned out and flushed, old gear oil can turn to sludge and will slow down gear spin, thus reducing engine performance. This is why transmission fluid change is recommended regularly along with engine oil changes.
Hypoid Oil Differences
Particularly for manual transmission and similar constructs, hypoid gear oil is the recommended lubricant. It's a gearbox oil, just like others, but the ingredients are different. This type of gear oil is mixed with additives designed to increase its resistance to breakdown under high temperature and mechanical pressure produced by hypoid gearboxes.
Regular Care Saves Dollars and Performance
As with all engine fluids and oil, regular maintenance and changing can extend the life of a vehicle and its performance. The most obvious benefit is lubrication; well-lubricated parts have less probability of chipping, breaking or grinding against each other under pressure. Another feature of oil is that it catches bits of dirt, metallic shavings from engine parts and other sediment. Flushing this oil fluid out regularly gets rid of all this material and exchanges it with fresh, new lubricant. Not changing the fluids will allow this sediment to build up, which then gets caught in the gears and causes breakdowns. Some experts recommend using synthetic gearbox fluid over natural petroleum-based products. Synthetic fluids do last longer and thus get credited with more performance. However, if you think about the flushing aspect, both oils then get changed at the same time, so the benefit is discretionary to the owner.
Hypoid gearboxes are an advancement in engine design and efficiency, but they require special lubrication to function properly. This additive-mixed fluid, hypoid oil, is the standard for transmissions and will continue to be until gearing design is changed to something more advanced. Both motorcycles and cars use hypoid oil, but given that motorcycles use more of a straight-on gearing design, cars are the predominant users.