28 Feb Motorcycle Wet-Clutch Performance

Posted at 14:47h in Amsoil Informational Study by
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Riding effectively demands confidence whether you’re a professional or a weekend warrior riding the trails near home. Confidence stems from experience with the bike and familiarity with the terrain and also derives from a 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 crossed the finish line.

For a typical motocross race, riders want firm, positive clutch lever feel as they revved the engine and 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. When the riders work up the through the gears, clutch lever should be crisp and consistence, not sloppy a loose. Each time riders maneuver around an obstacle, they want consistent, crisp shifts.

OIL IS KEY

The transmission lubricant plays a vital role in clutch feel.

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

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

The transition from the friction and steel plates spinning independently to become bound together is an example of dynamic friction. Once the plates are locked together and spinning in unison, this subjected to the principles of static friction.

Motor oil plays a vital role in both areas. 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 holeshot in a race or maneuver around obstacles. 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, can generate sufficient load to cause clutch plates to slip and the bike to surge.

Dirt Bikes

Confident Clutch feel is the number-one benefit we list on Amsoil Synthetic Dirt Bike Oil labels. It’s also the primary value proposition featured in our dirt bike ads.

The key is to use a lubricant specifically formulated for wet-clutches. Amsoil Synthetic Dirt Bike Oils (DB40, DB50, DB60 & 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.

COMMON CAUSES FOR WET-CLUTCH PERFORMANCE ISSUES:

  • Worn frictional plates
  • Glazed frictional plates
  • Stretched clutch cable
  • Worn or improperly adjusted engagement components
  • Distortion of clutch plates
  • Loss of clutch spring tension
  • Improper clutch pack height
  • Worn clutch basket
  • Engine modifications
  • Improper driver operation
  • Use of incorrect fluid

KEYS TO SELECTING THE CORRECT OIL FOR USE IN WET-CLUTCH APPLICATIONS:

  • Ensuring the oil meets the JASO and ISO frictional requirements set forth by the OEM.
  • Ensure the oil can provide high-temperature and oxidation stability.
  • Ensure that the oil offers shear stability and controls foaming.
  • Use the oil with the correct viscosity recommended by the OEM.

It is commonly thought that the use of synthetic oils results in excessive clutch slippage; extensive field and laboratory testing have disproven that theory. Synthetic based oils perform very well and do not alter the frictional characteristics of a wet-clutch and can actually improve their performance and longevity.

Use of the correct oil will ensure maximum clutch life and improved operation and performance. Amsoil power sports are designed for wet-clutch operation and provide all the qualities required for superior wet clutch operation.