Q. How do they work?
AAAAAAyyyyy!!!
Bar-end weight theory:
As your motorcycle runs, the handlebars form a resonant mechanical system. That is, the bars tend to shake at a certain frequency. If this frequency is any component of the characteristic frequency spectrum of your motorcycle, then the bars start to flap away, bothering your hands.
More technical:
As your motorcycle runs, the handlebars form a resonant mechanical system. That is, the bars tend to shake at certain frequencies, in certain ways. The lowest frequency, or fundamental, is a motion you could call, "flapping." This is where the center of the bars, between the clamps, is motionless, and the tips of the bars are vibrating most. This is typically the strongest mode of vibration, and the first one you should attack. If this frequency is any component of the characteristic frequency spectrum of your motorcycle, then the bars start to flap away, bothering your hands.
There are three ways to solve the problem.
- Stop the vibration. Many aspects of motorcycle design can come into play to check vibration at the factory. Details of crankshaft design, firing order and angle, mounting location, and counterbalancers can be used in concert to make for smooth running. If the engineers who designed your bike were skillful and careful about these factors, as they affect vibration, you can stop reading now- you don't need this product.
- Dampen the vibration. From an engineering standpoint, dampening means eliminating the resonant frequency of the handlebars. The proper way to do this is with a precisely designed flexible attachment between the vibrating part and a solidly mounted part, in other words, a shock absorber. The flexible attachment must be tuned to exactly oppose the specific frequencies of resonance, so vibration put into the bars will not be allowed to build up in them and hurt your hands.
Unfortunately, there is no proper way to dampen the handlebar motion, without a mechanical linkage from the outside of the bars to the frame of the bike, other than the bars. There are products out there which purport to dampen handlebar motion, but they can't technically "dampen" the fundamental frequency, since there is no linkage between the bar-ends and the frame.
That is not to say they don't "work." I haven't tried them, but I know many who are quite satisfied with them. Why, if they aren't dampening the bars from flapping? The higher-order harmonics of the resonant frequencies should be effectively reduced by, say, inserting a combination of weight and viscoelastic material into the bars. Due to the physics of the situation, the higher the vibrational frequency, the less weight is required to disrupt the motion, and the less solid the mounting point of the dampening system needs to be. So having a heavy elastomer all the way through the bars would be great for the higher harmonics, with the internal motion of the elastomer discouraging the formation of standing waves in the bars. But that lowest resonant frequency, the flapping motion, is typically the strongest. For that motion, all that elastomeric stuff in the bars is only as good as its mass. In other words, it operates just like plain weights- it lowers the resonant frequency, and discourages the tips of the bars from changing speed quickly.
This brings us to the last means of vibration control.
- You could change the resonant frequency.
When operating in this mode, the closer the weight is to the tips of the bars, the more effective it is. Solutions that involve equal mass throughout the length of the bars, have only a fraction of their mass working for the cause. The rest is dead weight. As a rule of thumb, any mass between the first two curves of the bar from center, is dead weight, and any mass at the tips of the bars is fully effective.
That's why our bar-ends are designed to maximize weight just outboard of the bars. They are 12.75 oz. per side, and every ounce hits home.
Q. How do bar-end weights change the resonant frequency and reduce vibration?
A. Resonant frequency is the frequency at which an object "rings" if it is moved. When you hit a tube with a hammer, and listen at the end of the tube, you are hearing the audible portion of its resonant frequency spectrum. The "fundamental" is the lowest note. In handlebars, this is the frequency made by the bars "flapping." By flapping I mean that the bar clamps stay put, while the tips move most. This fundamental frequency is typically the strongest frequency, thus the first one to attack.
Weights on the tips of the bars reduce vibration by moving the resonant frequency lower, away from the frequencies generated by the engine. This happens for the same reason that a heavier guitar string sounds lower, under the same tension, than a lighter one.
Because the effectiveness of a weight in reducing vibration this way reduces to zero as the weight approaches the bar clamp, I was careful to keep as much weight outboard of the bar-ends as possible. All the weight is concentrated where it is most effective- right near the bar-ends. All the weight is within 2.5" of the bar-ends. There's no dead weight as with solutions that go all the way through the bars. By moving the resonance lower, it typically moves further from the frequency of the engine, which reduces the build-up of vibration in the bars dramatically.
The other way to look at it is in terms of inertia. By solidly mounting the weights to the ends of the bars, the bar-ends gain a great deal of inertia, which means that they are much more reluctant to change speed. Since the flapping motion involves the bar-ends accelerating this way and that in rapid succession, any weight on the ends reduces this motion.
When you are trying to contain vibration by changing the resonant frequency,
solid-mounting is the way to go. Any flexibility to the mounting muddies the effect of the extra weight, hurting the cause.
