Wet clutches are widely used in motorcycles and dirt bikes. This term simply implies that a
clutch is lubricated with oil, as opposed to a dry clutch. A wet clutch typically lasts
longer and is more forgiving to operate than a dry clutch.
Frictional Performance Vital
As shown in the images, a clutch connects the engine and transmission via a series of
alternating friction and steel plates. Friction plays a big role in proper clutch operation.
To illustrate, imagine sitting aboard a motorcycle or dirt bike with the clutch lever
activated, idling at a red light or in a starting gate. The friction and steel plates
are separated, allowing the bike to run without moving. The light turns green or the
gate drops. As you let out the clutch lever, the plates squeeze together. The transition
from the friction and steel plates spinning independently to becoming locked 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.
Oil Chemistry Important
Motor oil plays a vital role in both areas. The formulation influences the dynamic
friction you experience, 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 pull away from a red light without the bike cutting
out, or start quickly and grab the holeshot in a race.
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, and you're riding. Oils with
incorrect frictional properties can allow the plates to slip in some circumstances,
which you'll feel as lost power to the ground. 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 V-Twin Motorcycle Oil (MCV,MCS,MVI), Synthetic Metric Motorcycle Oil
(MCF, MCT), 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