Speed Secrets: Shocks - What They Actually Do And How to Adjust Them

By Ross Bentley

August 12, 2014

Tuning shock absorbers used to be a bit of a black art, but over the past decade or so, it's become more of a science. David Murry tackles the topic of shock absorber tuning this week, and what I like most about his article is that it's written from the driver's perspective. - Ross
Shocks are one of those black magic components on a car. It took me a while to understand what they do and how to adjust them.
A shock has two functions:The first is to help control the springs over bumps and provide maximum traction. The second is to adjust the transitional roll couple (balance) of the car.

How a shock works: A shock provides resistance to compressing and rebounding open. That resistance is also separated into slow- and high-speed shaft movement. Slow-speed is considered up to about two inches per second movement. High-speed is usually two inches per second to about eight inches per second. (Editor's note: "Slow- and high-speed, as used with shocks, has nothing to do with the speed the car is traveling at. The speed of the shaft moving within the shock is what's being referred to.)

Shock adjustments: Different shocks have different numbers of adjustors.
  • Single has one adjustor that adjusts compression (also known as "bump") and rebound at the same time.
  • Double has two adjustors, one for compression and one for rebound.
  • Triple has three adjustors, one for slow-speed compression, one for high-speed compression and one for rebound.
  • Quadruple has four, one for each slow- and high-speed compression and rebound.
Adjusting shocks: 
First, letʻs adjust for bumps. Usually, you canʻt have a lot of both compression and rebound. That limits wheel movement and suspension. Some tracks and bumps require more compression/less rebound and others vice versa. When you drive, think about why the tire is leaving the ground. If it feels like a diving board, springing you into the air, you generally need more rebound to stop the springs from launching the car up. Sometimes, a bump or dip in the track causes the springs to compress more than desired, which builds too much energy in the spring and launches the car. In this case, you might need more high-speed compression to keep from compressing the spring that far, thus not needing as much rebound. If the car feels harsh and loses grip, then chances are you need less compression. The car isn't able to absorb the bumps because the shock has too much compression, not allowing the suspension to comply over the bump. There are times I will actually go look at the bump in the track (over which I'm losing grip), to see the shape of the bump, and to give me an indication of what's happening.

Second, let's adjust for transitions. We've adjusted the shocks for the bumps in the track, now let's look at the balance. The things that affect the steady state balance of the car are springs, sway bars, ride height, and aerodynamic components. Those things also affect the transitional balance. Shocks only affect the transitional balance, though, not the steady state. Slow-speed compression acts like a spring, but only for an instant. If your car is balanced well in a long turn, but the transition to entering that turn or if it oversteers in a quick turn from one direction to another, you would increase the slow-speed compression in the front. This transfers force to the front tires to give more grip to the rear. You can also add rebound to the rear to help hold the weight on the rear tires, giving grip there. All this is temporary, as the shocks bleed down and the car then rests on the springs/bars, etc. And all these adjustments are with the slow-speed adjustors.

Keep in mind that slow-speed adjustors affect high-speed some, as well, and vice versa. The adjustors can't be completely separated, by design.

A general way to adjust shocks is to start soft with all settings, so the car is compliant with the road surface. It will roll around and feel too soft. Slowly begin to increase the compression until the car does something you don't like (becoming harsh and losing grip over bumps, inability to turn, inability to put the power down). Then, soften a click or two. Then, do the same for rebound. Once there, evaluate the balance of the car and separate into steady state and transitional. Adjust the bars and rake for steady state; adjust the shocks (slow-speed) for transitional balance.

It can get a bit complex, sometimes! Just remember where your settings are, and try some things. But to begin, start soft and increase from there.
- David Murry
Web: http://www.davidmurry.com/
Exerpted from Ross Bentley’s Speed Secrets WeeklyFor more tips and additional articles on the art and science of racing, click here to subscribe