March 1990, Pages 66-67.
By Bob Price.
What a coincidence. A roommate during my college years was nicknamed the Bar Snake for his predatory practices at the local watering holes on Friday nights. Unlike this gentleman, the Bar Snake from C. P. Products looks as though it may actually have some intrinsic value. The Bar Snake is a length of precisely gauged rubber which is tightly installed inside a tubular motorcycle handlebar to damp out resonate vibration.
Vibration isnít usually a serious problem among todayís bikes, but the high frequency, hand-numbing variety appears occasionally and can be annoying. If the Bar Snake can reduce this, it will be a worthwhile accessory. I used my BMW R80 Boxer as a test vehicle. The handlebars and engine are both solid-mounted, so the engine pecularities are transmitted right to my hands. To measure the vibration before and after, I attached a felt pen to the end of the let handlebar after removing the grip, and measuring the arc drawn on a card as the handlebar vibrated with the engine. My tests were done at 1,200 RPM (idle), 3,000 RPM and 7,500 RPM (redline). To prevent the damping effect of my hands from interfering with the test results, I taped a lever to the throttle and activated it with a length of string.
Next I attached a sound-pressure-level meter to the handlebars, and recorded the readings in decibels at these same engine speeds. The meterís pickup was shielded from external noise with a chrome-alloy-steel damping sleeve. In other words, I stuck the microphone into a six-point socket from my took kit and then taped the socket to the handlebar. This way I could measure the intensity of the vibration. Finally I installed the Bar Snake and repeated all of the tests.
To install the Bar Snake, first you remove the handlebar grips. (the Bar Snake can only be installed in tubular handlebars, and only if there are no control cables or wires running through the bars. Shorter lengths of the Bar Snake may be installed in tubular clip-ons if there is a hole in both ends of each clip-on.) Next, you grease one end of the handlebar, and lubricate the Bar Snake with grease. Thread the installation wire through the greased handlebar end and out to the other side. Then thread the remainder of the wire through the hole in the end of the Bar Snake, twisting at least four inches of the wire back on itself a half dozen times. Then attach the other end of the wire to a stick and pull the Bar Snake through the last few inches with another piece of wire.
After installing the Snake, there was no change in the arcs drawn by the felt pen, but there was a five-db average reduction in intensity at each measured rpm. Since the decibel scale is logarithmic, this is a substantial reduction. But my R80ís worst vibration occurs during acceleration from one engine speed to the next. With the Bar Snake installed the meterís needle only climbed to 130 db. That may seem like a lot, but this is a direct transduction measurement, not the actual sound pressure; itís kind of like sticking the handlebar right up against your eardrum. Without the Bar Snake installed, the needle went off the scale (140 db-Plus) during speed transitions.
Perhaps the best test was taking the bike for a ride. The Beemer was much more pleasant, which is good, because the Bar Snake would be much tougher to remove than it was to install. My hands werenít nearly as numbed as usual. I did have one last test in mind, though, which included motion sensors set in a semi solid medium. Unfortunately, someone ate the Jell-O.
The American-made Bar Snake comes in three sizes for aluminum motorcross bars, standard bars or one inch (Harley-Davidson and others).