The crank pulley found on many modern engines is often called a harmonic damper. This damper is a thin rubber band, less than (1/8 inch) 2mm, built into the crank pulley. This rubber is used to absorb something called NVH, noise/vibration/harshness. Suffice it to say, this rubber is actually not very good at performing its intended purpose after as little as a few thousand miles. What happens to rubber after exposure to weather conditions such as humidity, snow, rain, etc? It often becomes brittle, hard, and crunchy. Can something with these properties actually absorb vibrations very well? Many NST customers have reported smoother running engines with NST pulleys, especially at idle. How is this possible if the rubber is such a vital important piece? As it turns out, the rubber is not as important as it is cracked up to be.