I am using H-D "E" oil, which I think is standard. My understanding from in here and elsewhere is fork oil viscosity can make a very big difference in ride and handling characteristics, but cannot verify for myself.
I am using the SE performance (heavy) fork oil. I only changed to help increase the dampening of the front end. I don't know how much "heavier" the performance oil is versus the type "E" oil.
thanks fur the replies ,, been readin up on it , Never changed the fork oil and the bike is 13 years old.... just forgot about it ,,, . Any way thinkin about goin with SE medium , I think that's 10wt. the stock oil E is 5wt. and the Front End always felt to Soft .
I don't know how much brand matters.. even tho Harley Davidson products don't touch my bike. But I used Bel Ray 30w based on what I read in the touring forums in my 06 FXST and I like it. I think for being stock it rides much better in the front. Just my .02
I just did a drop in kit and fork oil change on the wifes Sportster. I used the MOCO oils. I mix half standard (which is ATF) and half heavy. Extremely pleased with both the ride and handleing.