A reader asks: Why does AMSOIL Dirt Bike 10W-40 have the JASO MA rating and not the JASO MA2 rating like the AMSOIL Metric Motorcycle 10W-40? How important is this?

Our answer: Before we get into the finer details of JASO MA versus JASO MA2, let’s talk about the real-world difference between AMSOIL Dirt Bike 10W-40 (JASO MA) and AMSOIL Metric 10W-40 (JASO MA2).
AMSOIL Synthetic 10W-40 Dirt Bike OilThe starkest difference between these two products is the frictional properties and how this affects clutch performance. These oils are “tuned” and designed for optimum performance. Metric 10W-40 is designed for the street and Dirt Bike 10W-40 is formulated for severe off-road duty.

The Metric 10W-40 will provide smoother clutch operation, whereas the Dirt Bike Oil will be a little “grabbier”. The Dirt Bike Oil has to provide instant clutch engagement while launching out of a motocross starting gate, climbing up a very steep hill or to propel the bike through deep mud or sand. The Metric Oil is designed to provide smoother engagement in street riding situations.

That is not to say that the Metric Oil is any more prone to clutch slippage. We know of professional road racers that use Metric 10W-40 and have reported exceptional clutch longevity and superb performance. Both motorcycle oils are elite and will provide similar anti-wear protection.

What Is the Difference Between JASO MA And JASO MA2?

“JASO” stands for Japanese Automotive Standards Organization. Back in the 1990’s, JASO created motorcycle engine oil standards. One of the main motivations behind these motor oil standards was to signify which engine oils performed capably in wet-clutch operation.

Motor oils for automotive engines contain friction modifiers which can cause severe motorcycle clutch slippage. JASO created standards to offer consumers defined motor oil options for reliable wet-clutch performance.

AMSOIL Metric Synthetic 10W-40 Motorcycle OilJASO MA

The JASO MA standard was developed for 4-stroke motorcycles that use a common sump. In other words, the engine, transmission and clutch all use the same oil. To qualify for the JASO MA specification, a motorcycle oil must resist clutch slippage to JASO standards. The JASO MA spec also defines standards for engine and transmission wear.


As catalytic converters became prevalent on 4-stroke street motorcycles, JASO came up with an oil standard for these applications. The JASO MA2 spec determines whether a motorcycle oil is compatible with catalytic converters. It also has the wet-clutch slippage resistance standard, as well as engine and transmission wear limits.

To Sum Up

Dirt bikes and motocross bikes are not equipped with catalytic converters. Therefore, there is no need to formulate AMSOIL Synthetic Dirt Bike Oil to meet the JASO MA2 spec.

Questions? Contact us using the form on this page or call us at 1-800-748-5781.