Shock absorbers damp vibration by metering hydraulic fluid through an orifice located between rod and bearing surfaces of the rod guide. Most designs make rod guides from split-ring, glass-reinforced, bronze-PTFE bushings.

An industry-standard wear test for shock absorbers applies a biaxial load at two frequencies to simulate road conditions. Rod guides should last 1.25-million cycles without failure. However, the glass fibers tend to wear rod surfaces. Over time, concentricity and parallelism between mating parts degrades. This allows more fluid to pass through the orifice, compromising damping properties. But replacing the split-ring rod guide with a direct-bond bearing surface 45 to 50-mm thick greatly improves concentricity and parallelism over the design lifetime.