Designing Building and Tuning Shocks - How It Works

AFCO Explains the Basics of Designing, Building, and Tuning Shocks for the Street and the Track.

Stephen Kim Aug 6, 2013 0 Comment(s)
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Some suspension experts contend that shocks are the single most important set of components in the entire suspension. In light of all the fancy hardware on the market today—such as four-links, splined sway bars, aluminum spindles and control arms, and aftermarket subframe assembles that boast fully reworked geometry—this seems like a rather bold proclamation. Once analyzing basic suspension dynamics in closer detail, however, it all makes sense. While the springs support the weight of a chassis and absorb cornering loads and bumps, it's up to the shocks to control the motion of the springs. That means the shocks determine how quickly weight is transferred from front to back and side to side. Since getting the suspension to play nice with the tires—whether it's in a straight line or a cornering application—is all about optimizing weight transfer, optimizing the shock package is critical. Furthermore, since it's tough to swap out sway bars or springs at the track, adjusting shock valving is one of the most effective means of chassis tuning on race day.

Considering the substantial role shock absorbers play in the overall acceleration, braking, and handling equation, it's not the least bit surprising that manufacturers and race teams invest staggering sums of hours and research dollars into shock development. AFCO is one of the biggest players in the industry, manufacturing shocks for everything from 6-second door-slammers, to circle track cars, to street/strip warriors, to road race machines. To get the lowdown on the fundamentals of how shocks work and the cutting-edge technology that goes into their development, we sat down with AFCO's Eric Saffell for a chat. As an added bonus, since AFCO falls under the same umbrella of companies like Dynatech, we threw in some exhaust system tech as well. Here's the scoop straight from Saffell.

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Shock Anatomy

The fundamentals of how a shock absorber works are very easy to understand. Most hot rodders are already familiar with the body and shaft of a shock, which is what you can see from the outside. On the inside of the shock, there is a piston attached to the end of the shaft. Hydraulic fluid on both sides of the piston provides resistance to compression and rebound loads, and rings seal the piston to the inside of the shock body. While a tight seal ensures long shock life, the rings will grab onto the shaft if the seal is too tight, thereby increasing stiffness. Likewise, shims and valves on each side of piston control how much fluid passes through the piston, which determines the stiffness or softness of the shock. Shock damping can be manipulated depending how much oil passes through the deflective discs, valves, and shims. When you turn the knob clockwise on an AFCO adjustable shock, it puts more preload on the valves. This restricts the flow of fluid, which makes the shock stiffer. When you turn the knob counterclockwise, it removes preload from the valves. This allows more fluid to pass, which makes the shock softer.

Mono-Tube vs. Twin-Tube

Shocks utilize either a mono-tube or twin-tube construction, and each have their benefits and drawbacks. Twin-tube shocks have been around for a very long time, and have an inner body that slides inside an outer body. It's the workhorse of the industry, and the type of shock most people start out with in their racing careers. They can be used in entry-level circle track or drag cars, and double-adjustable twin-tubes can be used in high-end racing. While less expensive than mono-tubes, twin-tube shocks have a smaller-diameter piston, which limits damping precision. On the other hand, mono-tube shocks use newer technology and allow for more precise damping. Since mono-tubes don't have a small inner body, the increase in space inside the shock body allows for a larger-diameter piston. This extra surface area provides better response time. Overall, mono-tube shocks dampen more crisply and at a higher frequency. Furthermore, since they have a column of pressurized gas on top of the hydraulic fluid, they perform better in higher heat applications, like circle track cars that have their grille openings taped off. The downside of mono-tubes is that they are more expensive, and since they don't have an inner body, they are less forgiving of dents.

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Data Acquisition

The information gathered from data acquisition systems on race cars plays a very important role in helping AFCO design state-of-the art shocks. By monitoring shock loads and shaft speed, we are able to capture the dynamic weight transfer on circle track, road race, and drag cars. Once we map what's happening on all four corners of a car during a race, we can then plug that data into the shock dyno, and put a set of shocks through the exact same cycling that they experience on the track. This allows us to chart the force values, shaft speed, response time, and gas pressure inside the shock. Once this information has been gathered, we can then dissect each aspect shock of performance, and make adjustments to improve performance. In essence, data acquisition allows taking track data, bringing it into the lab, and optimizing the shock valving for a specific track and track conditions. The goal is to sculpt the damping curve to generate the performance we're looking for on the track, which might involve developing new pistons that have differently sized ports and orifices. The beauty of data acquisition is that you can gather lots of information from a very brief duration of time. In a drag car, for instance, you can break down a pass by how the shocks react during various stages of a launch, then string all that data together. This allows us to truly develop a shock package for a specific type of car on a specific type of track.