JASO T903 and T904: What Motorcycle Oil Standards Actually Mean (2023 Update)

Motorcycle Oil Standards: What They Really Mean

JASO T903 and T904: The Real Deal on Motorcycle Oil Standards (2023 Edition)

If your bike runs a wet clutch, your oil isn't just for the engine — it's pulling triple duty:

Lubricating the engine
Cooling and protecting the transmission
Keeping your clutch from slipping under load

That's why you need more than just“synthetic”on the label. You need oil that's been tested and approved to the JASO standards — especially now that they've been updated for today's bikes.

What Is JASO T903?

JASO (Japanese Automotive Standards Organization) created the T903 spec specifically for 4-stroke motorcycles. It’s one of the only oil standards that actually tests how oil performs on:

Wet clutch engagement
Gearbox shear
Friction stability
Emissions compatibility (2023+)

Most automotive oils? They don't care about any of that. They're built for cars — not for your bike's shared sump and screaming RPMs.

Tech Talk: T903 handles overall engine oil performance. T904 is the embedded test for clutch friction (we'll get to that below).

MA, MA1, MA2, MB — What They Mean

Grade	Clutch Type	Friction Level	Use Case
MA	Wet clutch	Moderate	Standard spec, safe for most bikes
MA1	Wet clutch	Lower	Older bikes or smoother feel
MA2	Wet clutch	Higher	Sport, aggressive riding, towing
MB	NO wet clutch	Very Low	For scooters/CVT only – 🚫 NOT safe for wet clutches

JASO oils are classified by how they perform in wet clutch testing

🛠️ Mechanic Talk: If your clutch runs in oil (wet clutch), MB is a no-go. Use MA or MA2. MA2 gives you extra bite — especially under torque or heavy load.

If you're wondering about the difference between MA vs MA2 oil, it comes down to friction performance and clutch feel.

Choosing the right wet clutch oil rating helps avoid slippage under load.

Chart showing JASO MA, MA1, MA2, and MB oil classifications and wet clutch compatibility

JASO Oil Classification Chart – MA and MA2 are wet clutch safe. MB oils offer low friction but are not suitable for motorcycles with wet clutches.

What's New in JASO T903:2023?

As of May 2023, the spec was revised to meet modern motorcycle demands — cleaner emissions, hotter engines, tighter tolerances.

Key Changes:

Phosphorus max lowered to 0.10%
Reduces catalyst poisoning, especially for bikes with emissions systems.
Evaporation (Noack) limit dropped to 15%
Means less oil burn-off and more consistent performance.
Outdated API specs removed
SG and SH are gone. Now requires at least API SJ — with SN Plus or SP preferred.
Updated friction test
Uses new reference oil (JAFRE-B23) and clutch plate material to reflect modern bikes.

These changes took effect for licensing on October 1, 2023.

What is JASO T904 and Why It Matters

T904 is the wet clutch friction test, now officially part of T903 as Annex A.

It uses a friction rig (like the SAE #2) to simulate real clutch behavior, measuring:

DFI (Dynamic Friction Index) – Acceleration grip
SFI (Static Friction Index) – How well the clutch holds at idle
STI (Stop Time Index) – How cleanly it disengages on shifts

These friction numbers are what separate MA1 from MA2. It's not marketing — it's machine-verified data.

Why Car Oil Can Kill Your Clutch

Automotive oils often use friction modifiers to improve MPG. That's great for sedans. But on a motorcycle?

It can glaze your clutch plates
Cause slippage under load
Lead to clutch fade or chattering
And destroy your transmission's synchros over time

Bottom line: If it's not JASO-rated, don't run it.

Picking the Right Oil

Riding Style	JASO Grade	Why It Works
Commuter / All-around	MA or MA1	Balanced grip and smoothness
Sport / Track / Aggressive	MA2	Higher friction, better clutch lockup
Touring / 2-up / Loaded	MA2	Grabs better under weight and heat
Scooter / CVT	MB	No clutch to worry about

✅ Most riders should choose MA2 — it's compatible, high-grip, and futureproof.

How to Read the Label

Check your oil bottle:

✅ “JASO MA” or “JASO MA2” — good to go
✅ “Meets JASO T903:2023” — even better
✅ “API SN Plus” or “SP” — matches emission tech
❌ “MB” or no JASO? Skip it

If you're shopping online, read the spec sheet. If they don't show the JASO rating? Assume it's not safe for your bike.

Final Word

Whether you wrench for a living or just love your bike, knowing the difference between MA, MA1, MA2, and MB can save you a clutch job — and a headache.

👉 Shop JASO MA2-Safe Motorcycle Oils

✅ Wet clutch approved

✅ Meets or exceeds T903:2023

✅ Lab tested — rider trusted