Adjustable Shocks

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Shock absorbers (or dampers, as some call them) are, in effect, hydraulic devices that resist chassis movement by passing oil through a set of orifices and valved passages. Inside an adjustable shock, manipulating the fluid movement through the valving of the shock changes the dampening characteristics. That means you can control how the suspension in your car or light truck functions (essentially fine tuning it for a given application). Many quality externally adjustable shocks are rather similar when it comes to adjustment. Once installed in the car, all changes are usually handled externally by way of the adjustment knob. After installation, the knobs on each of the shock absorber are accessible, either through the side of the spring (typical front applications) or on the body (typical rear applications).

Now what about the terms you usually hear when someone discusses shocks. The words "bump" and "rebound" (or "compression" and "extension") are often used. What's with that? Different shock absorber manufacturers use different lingo. Regularly, the terms "bump," "rebound," "compression," and "extension" are used interchangeably. Here's how it works: A shock absorber travels in two directions. It gets shorter (compresses) and it gets longer (extends). Some shock absorber manufacturers call this "bump" and "rebound," but that can get confusing. To get a grasp of what this is all about, pretend that you drive your car over a good old-fashioned parking lot speed bump. As it hits the speed bump, the action "bumps" the shock, which, in turn, compresses it. After you drive over the speed bump, the shock rebounds and extends (extension), allowing the wheel to move downward in the chassis. That's where we get the terms "bump" and "rebound."

Plenty of shock absorbers available today are adjustable externally. By far the most common are single adjustable. That means one knob is used on the body of the shock, and it controls the internal shock absorber valving. Adjustment is obviously a good thing since it allows you to physically "tune" the suspension in your car. But what's right?

Making Adjustments

The basic single adjustable shock setup works like this: Turn the knob fully to the softest setting (typically, this proves to be counterclockwise). The "end" of the adjustment (where it will not turn and click any further) is the softest setting, and it's often termed position 1. By turning the knob clockwise, each click will increase the shock resistance. On the other hand, the full stop counterclockwise has valving that's similar to a 90/10. What's a 90/10? It's an old drag race shock designed so the front end of the car would rise rapidly as the car accelerated then settled down slowly. The thought here was that weight would transfer quickly to the rear wheels and stay there. In other words, the front of the car is very "loose," particularly when it comes to rebound (extension), but relatively stiff when it comes to bump (compression). As you can imagine, that sort of setting (or non-adjustable shock) isn't much fun on the street, but it does go to show what the "softest" setting accomplishes on many adjustable shocks.

On a typical single adjustable shock, once you go past a certain point (for example, 6 clicks clockwise on our Strange Engineering sample shocks), the adjuster works primarily on extension (rebound). Moving all the way to the right (clockwise) will make the shock stiff. Moving all the way to the left makes it loose (the old 90/10 scenario). As you can see, even a single adjustable shock allows for a very large range of adjustment.

Adjustment Starting Point

According to the folks at Strange Engineering, the starting point for adjustment on a single adjustable front shock is as follows:

Street: Turn to position 4 or 5 (position “1” is full counterclockwise); for firmer ride, rotate clockwise.

Road Race: Turn to position 7 or 8 (position “1” is full counterclockwise; for firmer ride, rotate clockwise.

Drag Race: Turn to position 2 or 3 (position “1” is full counterclockwise); to increase weight transfer (front-end travel) rotate counterclockwise).

Here’s Strange Engineering’s starting point advice for rear single adjustable shock setup:

Street: Turn to position 4 or 5 (position “1” is full counterclockwise); for firmer ride, rotate clockwise.

Road Race: Turn to position 7 or 8 (position “1” is full counterclockwise); for firmer ride, rotate clockwise.

Drag Race: Turn to position 5 (position “1” is full counterclockwise). To plant the tires harder, rotate counterclockwise; to decrease wheel hop, rotate clockwise.

Double Adjustable Shocks

What about the more exotic double adjustable shock absorber? A double adjustable shock allows individual adjustment of the compression valving and rebound valving (typically while the shock is still mounted on the car). That means there is a separate knob devoted to compression and another for rebound. Given the increased sophistication of the internal valving, double adjustable shocks often cost much more than their single adjustable counterparts. They’re also far more complex, particularly when it comes to adjustment.

When it comes to double adjustable shocks, such as the Strange Engineering examples, the compression is adjusted by adjusting the marked knob from 1 (full counterclockwise) to 12 (full clockwise). Due to the precision of the adjuster, only a click change is necessary to make a noticeable change in the valving. The rebound adjuster is also extremely sensitive to change. Even one or two clicks will make a significant change in tuning the chassis. And there are plenty of available adjustments too. For example, the Strange Engineering shock shown in the accompanying photos has 12 rebound settings to choose from. That means you have approximately 24 settings per shock (and when both are combined, myriad combinations). Some manufacturers have fewer or more adjustments, but the operation is the same.

Which end of the car (front or rear) do you adjust first? If the car bounces on the gear change (more common than you might think), adjust the front shocks first. If the car wheel hops or has way too much body separation, then adjust the rear shock absorbers first.

Obviously, each vehicle will require a different setting when it comes to sophisticated double adjustable shocks. A good starting point or "baseline adjustment", particularly for rear shock adjustment is to initially set the rebound adjustment tight and the bump adjuster loose. At this point, you have to work your way through the respective adjustments (compression and rebound) until the suspension is responding for your specific application. The final settings front and rear that prove best for your vehicle must be found with some thoughtful trial and error and may change with conditions. That's why there are no real hard and fast rules when it comes to adjusting double adjustable shock absorbers (only "baselines"). This is also why racers of all sorts keep accurate records of what a specific shock setting accomplishes on each corner of their car.

As you can see, shock absorber adjustment can range from basic to extremely sophisticated. It takes some time to work out the final settings, but with the information presented here, you should be armed with a basic knowledge of what each knob does. See the photos for a closer look.

About the Author

A true hands-on "gearhead," Wayne Scraba has a diverse background in both writing and motorsports. Over the past two and a half decades, Scraba toiled as a magazine editor, technical editor, freelance magazine contributor, and has authored five automotive books. His background also includes racecar fabrication, muscle car and street rod restoration and construction, and operating his own automotive parts and repair business.

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