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Street Race Truck More... The Toolbox

Racing Shocks 101

6/8/2021
Tags: Tech, Tech, Race
What is a shock?

A shock is a timing device that controls the up and down movement on a race car. It will determine how fast or slow weight is transferred. Its purpose is to keep the tire on the racing surface.

Two Types of Shocks
Chart describing the difference between monotube and dual tube shocks.
Twin Tube/Dual Tube Shock

Also known as a two-tube or oil shock absorber, this device consists of two nested cylindrical tubes, an inner tube that is called the "working tube" or the "pressure tube", and an outer tube called the "reserve tube". At the bottom of the device, on the inside, is a compression valve or base valve. When the piston is forced up or down by bumps in the road, hydraulic fluid moves between different chambers via small holes or "orifices" in the piston. Finally, the shock energy is converted into heat and dissipates.

A dirt racing car equipped with twin tube shocks.
Pros and Cons

Pros Minimal gas pressure Minor Dents do not affect performance

Cons Smaller piston can limit dampening Lack of performance on a rough track

Mono Tube Shocks

Though it only has two pistons, the gas-pressurized, mono-tube shock consists of only the pressure tube. The pistons are called the working piston and the dividing or floating piston. They are completely separate from the shock's fluid and gas components. It also does not have a compression valve, because the role has been taken up by the dividing piston. Although it contains nitrogen gas, the gas in a mono-tube shock is under high pressure which helps support some of the vehicle's weight. No other shock absorber is designed to do this.

A dirt race car equipped with monotube style shocks.
Pros and Cons

Pros Provides better control on rough tracks

Cons Dents in the body can cause performance problems and will require service or replacement Hurts driver feel on smooth, dry or slick tracks

Small Shock Body Type
A pair of small racing shock absorbers.

A small body shock usually has 1 5/8” body and a smaller diameter shaft.

Pros and Cons

Pros Lighter weight helps with clearance

Cons Cannot dissipate heat causing shock fade if used on heavier cars and extreme heat

Small body shocks are meant to be used on Sprint Cars, Midgets, and Dwarf Cars. Cars that are not compatible are A modified, Stock or Late Model.

Large Body Shocks

Large body shocks have 2" bodies and larger diameter shafts.

Pros and Cons

Pros Very good on rough tracks as they can easily dissipate the heat More durable

Cons Causes clearance issues Relatively heavy

Large body shocks should be used on Modifieds, Stock Cars, Hobby Stocks and Late Models. Some of them can be used on sprint cars.

Shock Valving
Chart describing the different kinds of shock valving.
What Valving Numbers Mean

How much force is needed to compress or extend the shock? The higher the number the more force needed to move the shock. A valving number may differ per brand or even per series of the same brand.

How to Read Shock Numbers

AFCO, Pro and QA1 shocks will always have the shock series first then the stroke of the shock compression numbers first and rebound second. Bilstein will have also list the series of shock first in the number the stroke. However, they will list rebound first on the shock then the compression.

Tie Down Shocks vs. Easy Up Shocks

A tie-down shock is used to keep the weight from transferring back off a tire. It will be easy to compress this shock, but hard to extend. The easy up shock is used to keep a car hiked up or weight off a tire. These shocks are easy to extend, but hard to compress.

Adjustable Shocks
Adjustable shock absorber.

The advantages of adjustable shocks are that they give you the ability to tune your shock without having to purchase multiple shocks. Customers are usually able to dial in a wide variety of valvings with either single or double adjustable. The downfall is the cost of purchasing the adjustable shock at first.

Shock Maintenance
Examples of what to look for in old, worn shocks.

Shocks should be taken off the car, and checked out, after every night. You should check to make sure the shock can be fully extended and compressed without any issues such as soft spots or binds. The shock should also be checked for leaks around the shaft and body. Shock bodies should be checked for dents. These things should happen after every race night. You should also dyno your shocks at least once a year.

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