Donny’s Unauthorized Technical Guide to Harley-Davidson, 1936 to Present

Vibration Suppression does not mean Vibration Elimination 
Harley motorcycles have never vibrated less than they do today. However, the reason is suppression. I can assure the reader that without rubbermounting or counterbalancers that latter day loose flywheel truing specifications would generate much discomfort. However, vibration is part of the Harley personae. Vibration is one of the unique ingredients that make up the whole of the Harley….or at least it used to. 
Let me discuss what is normal and what is not. 
Some motorcycles have little or no vibration, but not our older Milwaukee Vibrators. For Harley riders, the goal is to control vibration, not eliminate it. Basic vibration is the by-product of the engine design. As long as the engine design remains as it is, there will be vibration. The 45-degree cylinder offset in all Big Twins going back to early in the last century is the design factor that contributes to the vibration that cannot totally reduce. 
This is one reason the V-Rod has a 60-degree cylinder configuration that eliminates much systemic vibration. The V-Rod goes two steps further: 
1. There are also counter balancers inside the engine. 
2. There are rubber mounts on the outside between engine and frame mounts thereby isolating the rider from vibration. 
Changing Harley’s Big Twin engine may be unthinkable, but there are things a rider can do to ensure buzzing keeps to a minimum. Balancing the flywheels will result a smoother running engine. Note that I said smoother, which makes for much more comfort but the some base vibration cannot eliminate. 
At best, we are using band-aids to fix the symptom and not the cause. In addition, just because an engine has a reputation for shaking, it does not mean it is entirely at fault. Harley engines are guilty of some, but not all sources of putting your hands and butt to sleep. There are a number of other steps the rider can reduce vibration without ripping the engine apart. 
Shimming or adjusting engine-mounts to get proper frame/engine alignment is one method. Dynamically, not statically balancing wheels and tires is another after ensuring they are in good condition. Other potential contributors are wheel sprocket/powertrain misalignment, worn handlebar rubber, and/or engine-mounts, worn out shocks and not servicing front fork oil. Any one or a combination of those non-engine items can result in a Harley vibrating more than it should. If the running train (wheels, forks etcetera) and powertrain do not align, there will not be the smooth transfer of horsepower. When one part works against another instead of with it, the result is vibration. 
Even owning a relatively new bike is no guarantee against excessive vibration. Factory wheel bearing spacing can be off, so that is something else to check during normal wheel maintenance. 
As a previous long-time shop owner, I can say that a minimum of 25-percent of all the mechanical parts sold is due to a lack of proper maintenance, installation, or care. 
Determining what is Normal 
Sometimes it is difficult to tell what is normal. If not sure, ask an experienced rider or mechanic to take your bike for a ride. The motorcycle owner may be the poorest judge if anything is wrong with the bike. Problems can develop gradually over time. When this occurs, the rider will adapt to the slow changes, not noticing a worsening condition as it creeps on. A fresh rider will spot something untoward immediately. 
Vibration Protection: Buy Cheap Parts 
Existing vibration can also dampen by choice of footpegs, handlebar rubbers, and handgrips. The fad of alloy billet footpegs and grips are not conducive to damping vibrations. I have a standing joke that the less expensive footpegs and grips are the most functional, long lasting and vibration resistant they will be. Conversely, the more expensive they become, the less functional and comfortable .The stock H-D rubber pegs and grips are the best available and cost the least. The most expensive grips and pegs that can cost ten times as much put your hands and feet to sleep within 50 miles...but they sure look good. With this said, I am a victim of Harley fashion myself.