Motorcycle oils typically need to be wet clutch compatible, and thus are free of friction reducing agents or any EP compounds that can cause clutch slippage, it relies mainly on hydrodynamic lubrication to do its job, hence the high viscosity
I hear ya Hemiscorpius lepturus, but a motorcycle's wet clutch is the farthest thing from extreme pressure! Spring pressure is carried by lots of friction pad area. But you seemingly agree with my hypothesis that V-Twin oil is seemingly targeted to Heavy Duty road bikes of Milwaukee origin.
Dominator is also targeted for wet clutch bikes, however, where again, EP is incurred in many locations BUT the clutch, so I now question my hypothesis, especially in that (seemingly, on further reflection) these big Heavy Duty designs run separate primary drive lube, unlike many/most(?) "racing" platforms that start out as street bikes, having primary drive and clutch
not isolated from gearbox, etc.
Whatever, I've topped up my SR500G with ~1/3 qt as of last night, and will be the Guinea pig for straight
Dominator 15W-50 as of next oil change. Not that such a placid cruiser is a tough test...
UPDATE: ...and re. "hydrodynamic lubrication," isn't this term related to plain bearings, and don't the iconic Heavy Duty machines in question feature roller bearing / anti-friction bearing bottom ends (with Siamese or so-called "split rods" sharing common plane)?
