While on a ride yesterday my riding buddy decided to open his bike up on a long stretch of desert highway. I decided to follow, it did feel good. My 2005 Wing keeps up well with my friends Concours 14. If we were on a track, not the street, I'm sure I would be a spectator. Anyhow, I got up to an indicated 120mph and a vibration started, which made me back off. It seemed to be in the chassis, not the handlebars or fairing. It was smooth right up to 110mph. It's a 2005, 68K miles, new rear drive unit and propeller shaft, recent Dunlop E4 tires, Centramatic balancers, Traxxion suspension all around. The easy answer is to not go that fast. I do wonder and worry that what ever caused the vibration is a fault, and will get worse, so I'm curious as to what caused it. Why is it OK at 110 and not 120? Do the Centramatic balancers not like high speeds? Front wheel bearings or steering head bearings at fault? Is the new propeller shaft not balanced well? So I'm wondering if anyone has had a similar experience and any ideas as to the cause of this. For the record, at 120mph, it felt like it still had a bit left .