Viscosity

Viscosity, in terms of motorcycle oils, refers to the thickness of an oil. A light or thin viscosity oil is commonly used in fork tubes while a heavier or thicker viscosity oil is often found in engines and transmissions. It is not uncommon to see multi-viscosity engine oils that are engineered to function within a range of viscosities. These special oils are designed for varied temperature ranges. A 5 weight oil would be considered light whereas an 80 weight oil would be considered heavy. An oil with a rating of 5W-20 might be suggested for wintertime use where the same motor might use 10w-40 in the summer when temperatures are hotter. The theory being that a lighter oil will remain more viscous in colder temperatures while a heavier oil will resist thermal breakdown in the summer heat.