The ongoing argument about whether the use of automotive formulated oils will adversely affect the operation of a motorcycle’s systems can be finalized with the following determinations.
1.) The wet clutch in a motorcycle works on the principle of friction.
2.) There is threshold amount of friction required to properly transmit the power produced by the engine to the output sprocket. When the amount of friction goes below that threshold the clutch slips.
3.) The engineers do not characteristically design any more than 15 to 20 percent more load-carrying capacity than needed into a clutch system for economic (it costs more for more plates) and/or ergonomic (the clutch lever is too hard to pull) reasons. These clutch systems are designed with a motorcycle graded lubricant as the specification. To reduce the inertial resistance the diameter and surface area of the clutches has been reduced, especially in the high-output sportbikes.
4.) The new automotive oils claim reductions in friction of up to 15%.
5.) Do the math.
6.) The above principles apply to EVERY wet clutch system.
7.) The above principles also apply to sprag-type starter system used on 95% of all motorcycles today, the only notable exception being Harley-Davidsons.
We sell motorcycle-graded oils for this reason. The relatively low production volume of these products causes the price to be higher, sometimes a hell of a lot higher. However when taken in context of the added expense per mile it isn’t really that much more, especially if a $250 clutch repair is avoided.
© Bill Whisenant 2007