Interesting... I would always use a fully synthetic oil, I reckon that's a no brainer. Oil is always thick when cold and thin when hot, that's why you have to warm the engine up before draining it. The numbers just tell you how thick when cold and how thin when hot. Quite how an oil can have a nought rating does confuse me though, would an oil that is even less thick when cold attract a minus rating?? The bigger question for me is not whether to use a fully synthetic oil or not but whether to use a non motorcycle-specific oil in my dry clutch engine. Bearing in mind that Ducati, for the SS bikes at least, used to recommend "any good quality, fully synthetic 5W40 oil". In line with your profit motive suggestions, I can't help suspecting that Ducati's recommendation for a motorcycle-specific oil is driven more by a deal with the oil manufacturer to recommend a high profit oil than because we actually need it or are better off with it.
