I ride an SR400. One of the recurring complaints among SR400 owners is vibration on long touring days. After about 300 km one-way, both hands were numb — pretty rough.
What the Power Beam is
The part with a reputation for cutting that vibration on the SR400 is the Power Beam from Y's Gear. It mounts to the frame and increases chassis rigidity, suppressing vibration. Fairly well known in the SR community.
Installing it
Re-applied the sticker myself before fitting. The fitting itself takes about 30 minutes if you're used to this kind of work. Two caveats: the rear-side bolt is awkward to torque, and the bolts tend to loosen after a while of riding, so periodic re-tightening is needed.
Riding it after
Power Beam reviews split between "couldn't feel a thing" and "noticeable difference." For me, the moment I rode after fitting it, I could feel the chassis rigidity step up. Vibration is clearly down too.
Before, the bike kind of swayed and floated through corners. After, it rides crisply. I came in skeptical. Now I'm convinced.
Buy the part. If you ride an SR400 and you're suffering on long-distance vibration — try it once.