In a car the engine is always separate from the gearbox so they have separate \ tranny oil for each. In car oil, there is more "friction modifiers" to help lessen the amount of friction on engine components and improve fuel economy. These friction modifiers that are added to automotive oils are what cause serious damage when used in bikes. The friction modifiers clog the clutch plates in a motorcycle's gearbox causing serious clutch slippage. To make motorcycles compact, manufacturers combine their engine and gear box into one casing. This means that everything is lubricated by only one type of oil including the valves, piston, transmission, because of this, we change our oil more frequently than a car. 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 heaps more for bike oil. Cheers Chris
