Dirt Bike Clutch Performance:

Ensure Your Dirt Bike Responds When Asked to Deliver

Confident clutch feel is the number-one benefit we list on AMSOIL Synthetic Dirt Bike Oil labels. But what does it mean?

Riding effectively demands confidence. It’s true whether you’re GEICO/AMSOIL/Honda professional Christian Craig or a weekend warrior haunting the trails near home. Confidence stems from experience with the bike and familiarity with the terrain. But it also derives from knowing your bike is going to respond the way you want for the entire ride. Riders want progressive, repeatable clutch-lever feel from the time they let out the clutch until they cross the finish line.

Dirt Bike Clutch Basics

Take, for example, the start of a typical motocross race. Riders want firm, positive clutch-lever feel as they rev the engine in anticipation of the gate dropping. When the gate drops, they want the bike to hook-up smoothly and with consistent power so they can grab the hole-shot. Again, as they work up through the gears, clutch-lever feel should be crisp and consistent, not sloppy and loose. It’s no different on the trails around home. Each time riders maneuver around an obstacle on the trail or accelerate down a straightaway, they want consistent, crisp shifts.


Motor oil plays a vital role in clutch feel. To see why, you need to know how a dirt bike clutch works.

The clutch connects the engine and transmission via a series of alternating friction and steel plates (see images at left). When the rider squeezes the clutch lever, the pressure plate separates the steel and friction plates, allowing them to rotate independently. This allows the bike to idle without moving.

As the rider lets out the clutch lever, the pressure plate squeezes together the friction and steel plates. This binds the engine to the transmission and moves the bike.

The transition from the friction and steel plates spinning independently to becoming bound together is an example of dynamic friction. Once the plates are locked together and spinning in unison. they’re subject to the principles of static friction.

Motor oil plays a vital role in both areas. The formulation influences dynamic friction, which is best thought of as clutch feel. Oils with incorrect frictional properties can result in inconsistent or loose clutch feel. This negatively affects your ability to confidently start quickly and grab the hole-shot in a race or maneuver around obstacles on the trail. The oil also contributes to the holding power, or static friction, between the plates once the clutch lever has been let all the way out. Oils with incorrect frictional properties can allow the plates to slip in some
circumstances, which you’ll feel as lost power to the ground. This is more common in motorcycles. A powerful V-twin riding up a hill, for example, can generate sufficient load to cause the clutch plates to slip and the bike to surge.

The oil’s additive chemistry has the greatest effect on performance. Friction modifiers, added to some passenger car / light truck motor oils to maximize fuel economy, can decrease the coefficient of friction within the clutch pack and result in excessive slippage. Extreme-pressure additives, commonly used in gear lubes to protect against shock loads and intense pressures, can cause excessive clutch slippage and related damage.

The key is to use a lubricant specifically formulated for wet clutches. AMSOIL Synthetic Dirt Bike Oil (DB40, DB50, DB60) and Synthetic Dirt Bike Transmission Fluid (DBTF) contain no friction modifiers or extreme-pressure additives. They’re dialed-in with the correct frictional properties to promote smooth shifts and consistent clutch feel while guarding against wear for long clutch life.

Comparison of Clutch Plates in extreme simulated start test after 32 simulated race starts. One set used the OEM oil and the other set used AMSOIL Synthetic Dirt Bike Oil.
How Does AMSOIL Synthetic Dirt Bike Oil Stand Up?
What Is The Difference Between AMSOIL Synthetic Dirt Bike Oil And AMSOIL Synthetic Dirt Bike Transmission Fluid?

This Article taken from the AMSOIL PC Magazine Spring 2019 edition

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