JASO MA, MA2 and MB, What the Classes Actually Mean

JASO T903 is the standard that sorts motorcycle four-stroke engine oils by how they behave against a clutch that runs in oil. The current revision is JASO T903:2023. It defines four performance classes, MA, MA1, MA2 and MB, and MB is the lowest friction class of the four. The class is printed on the bottle beside an oil code, and that code can be looked up, free, in a public register anybody can open.

Everything here comes from what the JASO Engine Oil Standards Implementation Panel publishes free. The standard's own text is sold by JSAE, so where a detail sits behind that paywall we say so rather than guess.

Before you touch anything

• Your manual is the only source for the class your machine wants. JALOS publishes the friction bands and nothing that maps a class to a vehicle type, so no page including this one can tell you. Settle that before you spend money.

• A printed class is a claim, not a certificate. The Panel does not test the oil. The classification is the submitting company’s own declaration, which is why the register check further down this page is worth doing.

• Getting it wrong has a named consequence. JALOS ties low friction oils to clutch slippage and transmission gear pitting wear on machines where one body of oil serves the engine, the clutch and the gearbox. That is the failure the standard exists to help you avoid.

• Two classes on one bottle is a labelling problem. The manual allows one performance classification on a container and no more, so a label showing two is telling you about the label rather than the oil.

• If you are doing the change today as well as choosing the oil, the hot oil, hot exhaust, fire and used oil hazards belong to that job. They are set out, with the EPA guidance on handling used oil, on our motorcycle oil change guide.

What JASO T903 is, and who publishes it

Two organisations are involved. The standard is written and issued by the Society of Automotive Engineers of Japan, JSAE. The filing and register system that puts a class on a bottle is run by the JASO Engine Oil Standards Implementation Panel, hosted by the Japan Lubricating Oil Society, JALOS. The Panel's Implementation Manual is free and is the source for this page. JSAE sells the standard itself.

The manual's cover is dated May 2023 and the standard carries an issue date of March 2023. Classification under the 2023 edition became allowed on 1 October 2023, and a filing made under the previous 2016 edition is maintained until 30 April 2028, so both markings can sit on a shelf at once.

The manual is blunt about why the standard exists. JALOS writes: "There are concerns that such low friction and low viscosity oils, when used in motorcycles, may cause clutch slippage and transmission gear pitting wear." That is the reason a motorcycle oil standard exists separately from a car oil standard.

The four classes, and what each one is

Each class is set by three friction indices measured in the standard's own clutch test: the Dynamic Friction Characteristic Index, the Static Friction Characteristic Index and the Stop Time Index, shortened to DFI, SFI and STI. The bands sit in Table 2.1 of the free manual, which we link to rather than reprint.

Class	What the manual establishes about it
MA	The whole higher friction band. An oil filed as MA sits in the range the standard was created to identify.
MA1	A subdivision inside MA, at the lower friction end of the MA range.
MA2	A subdivision inside MA, at the higher friction end of the MA range.
MB	The lowest friction class of the four. JALOS writes: "MB grade oils are classified as the lowest friction oils among motorcycle four-cycle oils."

MA1 and MA2 are not separate standards from MA. The note under that table says: "Submitter may on-file an oil which satisfies the MA specifications as a MA1 or MA2 oil depending on the indices specified in Table 2.1."

What the manual does not do is assign a class to a vehicle type. The mapping repeated elsewhere, that MB is for scooters or MA2 for sports bikes, is confirmed by neither JALOS nor JSAE, so we do not print it. Your owner's manual is the authority.

A bottle carries one class and only one. The manual states: "No permission of labeling of plural performance classifications." An oil advertised as MA and MB at once is not describing a JASO filing.

The friction test behind the classes

The test is Annex A of JASO T903:2023, titled "Motorcycles - Four-stroke cycle gasoline engine oils - Test procedure for friction property of clutch system". It was once a separate standard, JASO T904, merged into T903 as Annex A at the 2011 revision, which is why older bottles and older forum threads still mention T904.

The 2023 revision changed the reference oil, to JAFRE-B23, changed the friction plate, and moved the thresholds to match, so a class boundary under the current edition is not the same physical boundary as the identically named one before it. What the indices correspond to in physical units is not published in the free manual.

How the mark on a bottle is built

A filed oil is identified by an Oil Code Reference Number, built in four parts, set out in section 4.6 of the manual.

1. A single capital letter identifying the product type. The letter M is assigned to motorcycle four-cycle oils.

2. A three digit country code, taken from the international telephone dialling code of the submitter or the manufacturer.

3. Three capital letters, the lube oil supplier's code, chosen by the submitter.

4. A three digit control number, chosen freely by the submitter, and not reusable across that submitter's products.

A complete code reads as a letter, then digits, then letters, then digits, in one unbroken string, and the manual prints a worked example in Appendix 5. The printed mark also carries the performance class, the text JASO T903:2023, and a guarantee line naming the company that stands behind the oil.

What the mark does not mean

This is the part most buying guides skip. The Panel does not test the oil and does not certify it. JALOS writes: "the JASO Engine Oil Standards Implementation Panel does not guarantee the quality or performance of the oil, and takes no responsibility with regard to such matters." The classification is the submitting company's own declaration, on its own liability, and the manual even forbids a submitter from advertising in a way that implies the Panel approved anything. Read a JASO mark as a filing on the public record, not a seal of approval.

The register, and how to check a bottle yourself

The Panel publishes the whole list. The Filed Motorcycle Four Cycle Gasoline Engine Oil List is a free PDF at jalos.or.jp, giving brand name, submitter, oil code, performance classification and viscosity grade for every oil holding a current filing. The edition we parsed carries a face date of 1 September 2026 and 2,627 filings on it. Sorted by class, that is 1,771 filed as MA2, 470 as MB and 386 as MA.

Open the PDF, search for the code printed on the bottle or for the brand name, and an oil either appears with a class and a grade or it does not. The full procedure is on our page about how to check an oil actually meets your bike's spec.

Absence from the register means one thing only, that an oil has no current JASO filing, and reading a low count as a verdict on quality is a misreading of the document. We set that out in full, including what it does and does not say about the brands people ask about, on how to check an oil actually meets your bike’s spec.

What the split between the classes tells you

Those three numbers are the closest published answer to the question this page cannot answer directly. MA2 accounts for roughly two thirds of every current filing. MB is a clear minority of it. MA on its own, filed as the whole band rather than either subdivision, is smaller again. So a motorcycle oil carrying a JASO mark is, on the evidence of the register, most likely carrying MA2.

That is a fact about what oil companies chose to file, not a recommendation, and it still does not tell you what your machine wants. What it tells you is what to expect on a shelf. If your manual asks for MA2, you are asking for the ordinary case and should have little trouble finding it. If it asks for MB, you are in the minority of filings, and it is worth checking stock before you drive anywhere rather than after.

The register has one edge worth holding on to. It counts filings, not bottles, and it cannot see an oil whose maker never filed. A shelf holds plenty of the second kind.

Specifications you need to look up for your bike

Value	Why you need it	Where to find it
The JASO performance class your machine asks for	JALOS publishes no class-to-vehicle mapping	Owner’s manual
Whether the clutch and gearbox share the engine oil	Decides whether the friction class matters to your machine at all	Owner’s manual and factory service manual
The SAE viscosity grade for your machine and climate	A JASO class implies nothing about grade	Owner’s manual
The oil code reference number printed on the bottle in your hand	It is the part of the mark you can actually look up, and the only thing that makes a printed class checkable	The container label
Which edition of the standard the mark cites	The 2023 and the earlier edition use a different reference oil and different thresholds	The container label
The class recorded against that code in the register	The class on the label is the submitter’s declaration, the register row is the filing behind it	The Filed Motorcycle Four Cycle Gasoline Engine Oil List

When the bottle carries no JASO mark at all

Plenty of what you can buy carries no JASO mark, and that is not a defect in the oil. Filing is voluntary and it costs the submitter money. What it does mean is that you have no class in front of you to set against the class your manual asked for, so the requirement is unanswered on the available evidence rather than failed on a test.

What to do next depends on what your manual asked for. If it names a JASO class, an unmarked bottle does not answer it, and the next move is a different product or the dealer parts counter, not a substitution you reason your way into. If it names a manufacturer’s own oil or approval instead, JASO was never the requirement here, and no register stands behind that kind of specification, a gap we set out on how to check an oil actually meets your bike’s spec. And if your machine keeps its clutch and gearbox out of the engine oil, the friction class has no bearing on the clutch at all, although your maker may still name a grade and a product.

One thing here does genuinely belong in a shop. If the clutch is already slipping, that is a mechanical finding, and it wants diagnosis before anybody changes oil and hopes.

Related checks

• Can you use car oil in a motorcycle?

• What 20W-50 actually tells you, and what it does not

• How to check an oil actually meets your bike's spec

• How to change motorcycle oil, and why there is no single procedure

Frequently asked questions

Is MA2 better than MA?

Better is not what the classes mean. MA is the whole band, MA1 its lower friction half and MA2 its higher friction half. Higher friction is not higher quality, it is a different target. What your machine wants is in its owner's manual. We have not tested any oil and we do not rank them.

Can I use a JASO MB oil in a bike whose manual asks for MA2?

If your manual asks for MA2 then MB is not what it asks for. JALOS states a concern that low friction oils may cause clutch slippage and transmission gear pitting wear, and MB is the lowest friction of the four. JALOS does not publish a guarantee that a given MB oil will slip a given clutch, so treat this as a mismatch against the specification rather than a prediction of failure.

My bottle says JASO T903:2016. Is it expired?

Not automatically. Filings under the previous edition are maintained until 30 April 2028, so that marking can still be current. Settle it with the oil code rather than the edition year, and look the code up in the free register.

Where can I read JASO T903 itself?

The Implementation Manual is free from JALOS and is where every rule on this page comes from. The standard's own text is sold by JSAE, and the requirement tables inside it sit behind that paywall. We have not reproduced them, and a page that prints those limits without saying where it got them is worth a second look.

Does a JASO class tell me which viscosity to use?

No. They are separate systems answering different questions. The JASO class describes friction behaviour against a clutch. The viscosity grade comes from SAE J300 and describes flow. A bottle carries both because neither covers the other, which we go into on what 20W-50 actually tells you.

About this guide

Published by MotoGearRater. Universal procedure only, with no model-specific specifications. This guide has not been reviewed by a qualified motorcycle technician, and we say so rather than implying a review that has not happened. Read our editorial standards.