Short answer
JASO T903 is a standard from the Japanese Automotive Standards Organization for four-stroke motorcycle engine oils. Its main job is to sort oils by how they behave with a wet clutch that shares the engine oil, using the categories MA, MA1, MA2 and MB. Your owner’s manual tells you which category and viscosity grade your bike needs.
Why motorcycles needed their own oil standard
Many motorcycles run the engine, the gearbox and a wet multi-plate clutch on one oil supply. Passenger-car oil categories are written for cars, which have no clutch in the crankcase, so they say nothing about whether an oil lets a clutch grip cleanly. Some car oils are formulated with friction modifiers for fuel economy, and those additives can work against a clutch that needs to hold under load.
JASO T903 fills that gap. It starts from an existing engine oil quality level and then adds motorcycle-specific requirements, the most important being a clutch friction test. The result is a label that tells a rider whether the oil was intended for a wet-clutch bike or for a scooter with a separate drive system.
How the categories are assigned
Oils are classified using the JASO T904 clutch friction test, which measures three indices: dynamic friction, static friction and stop time. Oils that land in the higher-friction band are MA, and MA is divided into MA1 and MA2. An oil earns MA1 or MA2 only if all three indices fall inside that sub-range; an oil that straddles the two is simply labeled MA. Oils that land in the lower-friction band are MB.
Beyond friction, the standard sets requirements for physical and chemical properties and requires the oil to meet one of a list of recognized API, ILSAC or ACEA engine oil categories as its baseline quality level.
The current edition and what changed
JASO T903 has been revised several times since MA1 and MA2 were introduced in 2006. The current edition is JASO T903:2023. According to additive and test-laboratory summaries of that revision, it dropped API SG and SH from the list of acceptable baseline categories, so new registrations must start at API SJ or higher, and it added API SN Plus and API SP at the top of the list.
The 2023 edition also tightened limits on phosphorus content and Noack evaporation loss and updated the friction test with a new friction plate material and a new low-friction reference fluid. Oils registered under earlier editions may still be on the shelf, which is why labels can show different edition years.
Registration and reading the label
JASO T903 works through registration: the oil marketer submits test data and the product is added to JASO’s published list of registered oils. Registered products typically show the JASO mark with the category and a registration number. Some bottles simply say an oil “meets” a JASO category without the mark, which is a claim made by the marketer rather than a registration you can look up.
When you compare oils, check three things on the label and in the product data: the JASO category your manual asks for, the SAE viscosity grade, and any motorcycle-maker approval the manual lists.
Frequently asked questions
Is JASO T903 the same as JASO MA?
No. JASO T903 is the standard itself. MA, MA1, MA2 and MB are the categories an oil can be assigned under that standard.
Does JASO T903 apply to two-stroke oil?
No. JASO T903 covers four-stroke motorcycle engine oils. Two-stroke gasoline engine oils are covered by a separate standard, JASO M345, with grades FB, FC and FD.
Can I use a car oil if it has the right viscosity?
Only if your owner’s manual allows it. A car oil carries no wet-clutch friction rating, so a motorcycle that calls for JASO MA, MA1 or MA2 should get an oil that lists that category.
General maintenance information. Always follow your vehicle or equipment manufacturer’s requirements and the current product data. Questions? Email [email protected].
