Also see Changing Fork Oil
Fork oil, depends on weight and preference of fork action. Most of us go with either 10W or 15W fork oil. I have 10W Amsoil in my forks which works well with Progressive springs. You can also use Auto Trans Fluid (ATF) which is a great quality 10W oil and way cheaper than fork oil.
What I've found to work good in forks is 5W for riders up to about 140 lbs, 10W for riders 140-185 lbs, and 15W for riders over 185 lbs. ATF was the recommended fork oil for many years, but it's inconsistant. It varies from 7.5W to 15W and there's no way of knowing what you're getting. It varies from refiner to refiner, and from batch to batch from the same refiner.
Thanks, I didn't know that about ATF. I do know that fork oil is that way. There is no standard for it. Brand A's 10W might be equal to Brand B's 15W. That's one reason I went with Amsoil because they're probably closer to what racers spec out as a given weight/preference.
Supposedly, the fork oil is closer to a standard wt than ATF. When fork oil first started appearing and bike manufacturers stopped recommending ATF a lot of comparison tests were run to show that real fork oil was worth the difference in price. That's the reason I stick with BelRay fork oil. They've been around long enough I know what to expect out of each weight and it seems to be the most commonly used in repair shops.
I used Bel Ray fork oil for years...as did most of the riders I knew. Is a bit higher in price..but , yeah , you know what your getting
If I were you..I'd go with the 15w fork oil. Buy Bel-Ray fork oil..it works and you know that the weight is correct .( it has anti-foaming agents in it...a good thing) Knifemaker
I emailed Bel-Ray and asked what wieght fork oil to use for our VN750. They recommended 15w to me as well. Sempai