Oil, religion or science?
30 years ago, the difference between the oils on the shelf labeled for auto use and those labeled for Motorcycles, was moot. This was before the EPA's successful campaign to remove heavy metals from automobile exhaust. After removing lead from fuel, they still noticed zinc in the exhaust discharge, also a heavy metal that interferes with catalytic converter function, and convinced the auto and oil industries to reduce or curtail its inclusion in the oil additive package.
Who cares? Well, operators of machines other than automobiles should. Why?
The base stock petroleum oils are indeed few in number of available manufacturers. What differentiates some, but not all, labeling is the additive package blended with the oil before it is bottled. While the exact same oil and additive package can appear with different labels. Oil blends suitable for engines with integrated transmissions are not on the list of suitable oils recommended by todays auto manufacturers due in part to EPA influence.
Just like lead was a good lubricator of non-hardened cast iron valve seats in fuel. Zinc is a very good anti-wear additive for meshing transmission gears. The synthetic additives that make oils behave as thicker oils when heated (multigrade oils) are called long chain molecules. These long chains are chopped up in transmission gears over time and the oil then loses its thick oil behavior and reverts back in properties of its much thinner base stock. This thinner oil is just not as good at cushioning the high load gear tooth faces as thicker oil does. However, zinc does provide a surface antiwear coating similar to what heavier grade oils can provide. Most autos don't need the zinc as they have separate chambers to house a lubricant suitable for transmission use.
When modern formulations of auto oil are used in motorcycles, it's multiVis properties are rendered useless after a couple hundred miles. If you reduce your oil change interval three or fourfold, your transmission should wear as well as if you used an oil with a zinc additive such as those labeled for motorcycle use.
I believe it is unfortunate the oil distribution marketing departments foster and rely far more on the religious aspects of oil purchasing habits, rather than the more informative scientific approach regarding machine needs.
Indeed, the recommendation to "Get some education regarding your hobby" is indeed a good one.
But hey, it's your transmission, put whatever you want in it. Moly is a good replacement for the zinc for all the sliding and shearing forces in the engine/trans. Pity it also makes the clutch slip, too.
Cheers,
