According to
Mobil: Motorcycle and automotive oils differ in two areas. The first concerns common sumps, or the use of motor oil, to lubricate and cool the transmission. ... In a motorcycle, where the transmission may be lubricated by the engine oil, an engine oil that does not have the same level of friction modification (for fuel economy) of a typical passenger car engine oil will provide better transmission performance in terms of transmission lock-up and slippage. So motorcycle engine oil does not contain the friction modifiers of a passenger car engine oil. The second area of concern for motorcycle engine oils is that they tend to shear (breakdown viscosity) more quickly than a typical passenger car. Mobil 1 motorcycle oils are designed to provide exceptional protection against viscosity loss.
Similar claim by
Husqvarna which also says: Motorcycles require very little and/or no friction modifiers to help improve clutch friction and to prevent clutch slippage. But to make up for this lack of friction modifiers, motorcycle oils use higher levels of anti-wear additives such as ZDDP, also known as phosphorous, to limit engine friction and wear. Since motorcycle oil has extra anti-wear additives and is lubricating so much more than automotive oil, you can expect to pay anywhere from $9 to $15 a quart.
However, a Google search indicates that independent testers can find no appreciable difference. Here is an article from
Motorcycle Consumer News posted in Ducatimeccanica.com. Which does not support the use of motorcycle specific oils but does support the use of synthetics....
