Racing Shock Absorbers - Shocks 101

Part One of Two
Shock absorbers will elicit an emotional response from any racer. Yet, this is a part of the suspension that is shrouded in mystery. That's true not because shock absorbers are a complex part, but because not everybody is free with information on the operation and tuning of shocks. Racers are at times a tight-lipped lot. Knowledge that equates to a winning setup is an advantage, and you do not want to give your competition any advantages.

It is easy to look at a spring and understand what it does, no matter if it is a coil spring, a torsion bar, or a leaf spring. Visually, it is very easy to understand how it works and the role it plays in the suspension. The same can be said for A-arms, spindles, and axles. It is easy to understand the roles these parts play in the suspension's operation.

Shock absorbers, though, are somewhat of an unknown. The biggest driver of the mystery is that many racers do not really understand the role that shock absorbers play in how the car feels to the driver, how the car responds to changes in tires and springs, and ultimately, how the car as a whole responds to the track.

From a simplistic view, all the shock absorber has to do is keep the tire in contact with the ground as the suspension articulates. The shock absorber converts the up-and-down motion (kinetic energy) of the suspension into heat, which is transferred into the shock through oil that is forced through orifices or valves in the shock. This causes the shock to dampen or control the movement of the suspension.

Without shocks, the springs would keep oscillating until the wheel movement caused by a bump in the road dissipated or until the car was stuffed into the wall. With a set of shocks we can control the bounce or oscillation and keep the wheel and tire combination planted on the road as the car travels over the track. We can adjust the shock to suit a specific condition or make the car behave in a way that we deem desirable.

So, why are shocks such a mystery? First, the vocabulary surrounding them is often misunderstood. Let's look at definitions of terms used to describe the shock and its activity.

Dive: A pitching motion, usually in reference to deceleration. The sprung mass of the vehicle moves forward, the front of the car compresses the springs, and the rear of the vehicle extends the springs. As the car slows under braking, it dives forward. This places the front shocks into compression and the rear shocks into a rebound condition.

Squat: A pitching motion, usually in reference to acceleration. The sprung mass of the vehicle moves rearward, the front of the car extends the springs, and the rear of the vehicle compresses the springs. This places the front shocks into a rebound condition and the rear shocks into compression.

Compression: The act of compressing the shock. The shaft moves into the body of the shock. During compression, the shock becomes shorter and the wheel travels in an upward motion.

Rebound: The shock extends and the wheel travels downward during the rebound stroke.

Dive and squat are attitudes that the car assumes as it accelerates or decelerates during any given lap. The adjustability or tunability of the shock absorber enables the racer to make the car adapt to changing traction conditions. The setup utilized with the shock absorbers determines how the racer adjusts dive and squat. Yes, other suspension parts play a role in dive and squat-such as antiroll or sway bars-but the shocks are the major players in the attitude the car attains as it travels around the track. The attitude the car assumes in any given condition is directly influenced by the settings that affect the compression, rebound, and valving of the shock absorbers.

Twin Tube: Just as the name implies, there are two tubes used in the design of the hydraulic portion of the shock. This shock utilizes an inner and outer tube and is usually found in OEM applications. The inner tube houses the piston and is commonly referred to as the pressure tube. The outer tube is used to store fluid, and in some applications the outer tube can be pressurized with a gas, usually nitrogen.