Transmission Lubrication
Motorcycle transmissions, just like all gear-based automotive transmissions can quickly degrade a multi-viscosity, or multi-grade engine oil. Conventional car and truck transmission oils have specific EP, and other specialised anti-wear additives, but these EP additives are not suitable for the combined application of lubricating the engine and transmission with the same oil, as is the norm in motorcycles.
Multi-viscosity oils contain viscosity improver chemicals known as VIs that keep the oil from becoming too thin at high temperatures. The VIs are large chemicals that tend to shear between the cogs of a motorcycle transmission. That can have the effect of reducing a 10W-40 oil to a 10W-30 in a relatively short number of miles.
One solution to shearing is to use single weight oils, which do not have VIs and are not susceptible to degradation in the transmission. However, single weight oils do not flow well in cold conditions, reducing overall lubrication until the oil has warmed up. An alternative is to use a synthetic oil. Synthetic oil are designed to have good cold-flow properties yet maintain high viscosity with fewer VIs.
Read more about this topic: Motorcycle Oil