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Originally posted by wittymonkey
Q: What is harmonic vibration (sometimes called sympathetic harmonic vibration)?
A: Every item on a motorcycle (or in a car, etc) has some frequency that it naturally wants to resonate at. Just like a bell or a tuning fork has a specific frequency when you ring it, parts of the bike have the same tendency, especially the handle bars (which are a hollow tube, and thus like a type of bell).
If you take two tuning forks which are tuned to the same frequency, start one vibrating, the other will start vibrating too if it's within audio range. Why? Because the sound (which are vibration waves through air) are at exactly the right frequency to push against it at exactly the right instances to build up the second tuning fork's shaking. This is called harmonic vibration. It doesn't even have to travel through air -- it can just as easily travel through any solid material (such as an I-beam, or in our case, the frame or triple-trees of the motorcycle).
Thus, when something in your engine, transmission or wheels happens to hit the right frequency to hit the frequency of the handle bar extensions, they vibrate... and if it happens to be at a frequency that messes with your nerve sensors, you get tingley hands (which can lead to more complicated problems, including Raynaud's disease aka Raynaud's syndrome).
So how do you stop it? You have two basic methods:
By changing the mass of the bell or the tuning fork, you change the harmonic frequency -- in the same sense, the Katana normally uses a very heavy (compared to most bikes') set of bar-end weights designed specifically to help keep the harmonic frequency out of the range of what the bike normally sees. Increase the bar-end weight, or the bar-weight itself (by filling it with lead or BB's & silicone or epoxy, etc), changes it's vibrational frequency.
The second method is to track down the origin of the vibration and stop it from happening there (such as sync'ing the carbs and doing a valve adjustment, to the more extreme "balancing the engine's rotating masses").
Obviously the first method is easier. Thus, if you removed the stock bar-end weights (or replaced them with light-weight replacements), put the stock ones back on. Or get even heavier ones. And then start thinking about weighing down the bar extensions themselves more heavily (commercial products like the "Bar Snake" fill this niche, as well as the home-remedies I listed above).
On a separate note: if either of the bar extensions are unevenly bent compared to the other, this sets up a different kind of vibration that can't be cured by increasing the mass of the bars -- the only good solution is to replace the bent bar with one that isn't bent. This is a frequent occurance in bikes that have been dropped and the bend is small (a few degrees, barely even noticable) -- taking the bars off and laying them against each other will let you see immediately if one is bent at a different angle than the other.
Finally, a word on nerve damage, Raynaud's syndrome (or Raynaud's disease, sometimes called Renauld's disease) and long term risks of riding with bad vibrations. If your hands regularly get tingley from riding, you need to address this issue by either undertaking one of the above fixes or by otherwise damping out the vibration (such as use of gel-palmed gloves, throttle rockers, and/or cruise controls). Failure to do so can result in multiple medical issues with your hands/fingers/wrists, including permanent damages and even cellular death (which can lead to gangrene and amputation in the most extreme of cases). The vibrations can cause disruption of the blood supply in the smallest capillaries, depriving the cells of oxygen, and can also cause your nerves to basically short-wire themselves from too much systematic false input (leading to symptoms of pain or numbness that may be permanent, as well similar reactions at the hands when emotionally triggered in the future). White splotchiness on the palms is often an early symptom... Unfortunately, (according the FDA and the center of rare diseases) much of the info out there on Raynaud's is poor, inaccurate or dated -- the most common sufferers are those who used power tools or other vibratory devices held in their hands for years prior to diagnosis; the subsequent symptoms (post-onset) are usually quoted as being causal when in fact they rarely are. Cold exacerbates the problem because blood flow into the capillaries is already restricted by the body's natural attempts to restrict heat loss, and thus in cold weather this is even more likely to occur.
The picture below are the hands of a 43-year old male sufferer -- and no, he did not just let go of a set of handlebars or other item; the discoloration is now permanent from the damages associated with Raynaud's:
Look up Renauld's disease for more info.
Good Luck!
=-= The CyberPoet
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