The basic principle of balancing weights
For the most part, balancing weights are incorporated to single-cylinder engines. Yet, you can find some on multi-cylinder engines. The operating principle is that counterweights rotate in the opposite direction of the crankshaft (as illustrated below):


Diagram number 1 shows the inertia created by the connecting rod and piston. This inertia (100 percent) is countered by the centrifugal force generated by the crankshaft (50 percent) and counterweights (25 percent for each weight).

Diagram number 2 shows zero percent inertia. The centrifugal force generated by the crankshaft's weight is offset by that of the balancing shaft, which rotate in the opposite direction.

Diagrams number 3 and 4 illustrate the same phenomenon as in 1 and 2 but the other way around.

As previously mentioned, balancing weights make the engine block larger and heavier, especially with chain-driven engines. Whether it's a motorcycle or ATV, this balancing system is very important; without it, the engine simply would not withstand wear and the resulting vibrations would make riding much harder. Numbness in the hands and feet would ensue. I'm sure you know what I'm talking about...

Some manufacturers have addressed this issue with a simple solution: the addition of rubber footrests and grooved handlebars with thin rubber rings near the tips. They mitigate unwanted vibrations and numbness for a more comfortable riding experience.

So, for your next motorcycle or ATV purchase, ask the dealer about engine balancing features on the vehicle. A thickly padded seat is not the only thing that favors overall comfort.