Newultraclassic was right on. I have a '75 Superglide. It vibrated miserably from 55mph, and 65 was no fun at all. I aligned the upper motor mount, put in baffles, tightened everything, and I try to stay on engine tune and vac. leaks. (I am overdue for all new rear drive sprockets.) Vibes are waaay down. After all this was done and I was sure that all mechanical things were Best available, I started with grips, pegs, made a fork brace to kill the "tuning forks" and tightened the seat to lower vibes. She will cruise the interstate very nicely now, and nothing has the sound of the old Harleys. The key seems to be to get it ALL tightened, aligned, and good to go. It does little to align the upper mount, but not tighten the primary bolts and the tranny bolts, and the pegs, and the kick stand, etc. Once ALL is tight, I just check it from time to time. Mine has been VERY reliable, left me stuck less than my V-Max.