The wet clutch this standard exists for
Most motorcycles run a clutch in the same oil as the engine. That oil has to lubricate bearings and gears while still letting friction plates grip each other — two requirements that pull in opposite directions. Car engines have no such constraint, so car oil formulations are free to reduce friction everywhere, and an oil that does so can make a wet clutch slip.
What the designations distinguish
MA designates oils suited to a wet clutch; MB designates oils for applications without one, such as a dry clutch or an automatic transmission. They are different uses rather than different grades, and they are not interchangeable in either direction. The MA family is further divided, and the divisions are published by JASO.
Why the viscosity grade does not answer the question
A grade such as 10W-40 describes how an oil flows cold and hot. It says nothing about friction modifiers. A car oil and a motorcycle oil can carry the same grade and behave completely differently at the clutch, which is why the grade and the specification are two separate lines on the same label and both have to be read.
Where the answer for a given machine lives
In that machine’s own manual, as a viscosity grade and a specification together. This site reports what a container publishes; which pair an engine requires is settled by the manufacturer of the engine.
Questions riders send in about this
Can I use an MB oil in a wet clutch?
The designations exist to distinguish the two applications, and the machine’s manual states which it requires. That instruction is the answer rather than anything on a comparison page.
Do all motorcycle oils carry a JASO marking?
Not all, and where it is absent the container has not stated anything about this property. An absent marking is information, not a pass.
Last reviewed 18 September 2026