I'm a mechanic at a goverment fleet. I've done days of oil reseach. We run synthetic in our emerency vehicles now. But that only happened after we did a few oil analyst. I believe Redline 20/60 HD oil is the best oil for a Harley. It's what I run in the summer. 20/50 in the winter. I've done an oil analist on my bike after 4000 miles and it came back perfect. Chemist said I could have used it for at least another 2000 maybe more. That was after a long hard run through Death Valley last fall (1800 mile trip) I suggest doing an oil analyst on your next oil change, it's the only scientific way to determine what condition your oil is in and how much longer you can run it or if you ran it too long.