When it comes to springs, a little knowledge can go a long way in performing better on the track. We are not spring experts, and if you are reading this series, you probably are not either. But, using our industry resources, we hope to provide you with a working knowledge of automotive coil springs.
We don’t want to mislead you, automotive coil springs are a very complex subject — chassis setup is even more complicated. These subjects are so large that entire industries are built around the different types of springs and chassis setups, even for the different types of cars and classes in motorsports. There is a global professional association for spring technology, the Spring Manufacturers Institute (SMI), which works to meet the key issues of the industry worldwide since 1933. SMI holds routine meetings and seminars covering quality, material, technology, and government regulations.
We’re going to take a look at how to correctly select and set up springs in a series of articles with the help of the manufacturing specialists at Hyperco Springs (MW Industries, Inc).
Compression springs utilized on vehicles are commonly made out of steel — probably high-carbon steel. Almost all metals are elastic and when flexed, bent, or stretched, they try to return to their original shape. In that sense, metal is said to have a memory. Knowing that metal is elastic is important to racers setting up their chassis for competition. If metal is elastic, and coil springs are made of metal, you can correctly assume that springs stretch, flex, and bend, as they are used on the track.
We say coil spring, but what we are really talking about is helical compression springs. Helical compression springs are usually made from round wire and wrapped in cylindrical form with a fixed pitch. Compression springs produce linear force by pushing back against the force applied to it. Any weight, or force, applied to compress the spring down will cause the spring to push back against the weight as it attempts to return to its original state.
Our series will start with the conventional compression coil springs and branch out to coil over springs, Ultra-High-Travel springs, stacked spring systems, dual-rate springs, and even pull-bar springs for dirt modifieds.
Terms And Definitions
Our Hyperco friends tell us abbreviations, acronyms, buzzwords, and engineering tech-speak exist in every industry. In order to get the most from this series of articles, you need a common understanding of spring terminology. They have provided several racing and spring-related terms and phrases you might need to know as we progress in the series (in alphabetical order):
- Active Coils – A helical compression spring is usually made up of many coils. Active coils are the spring coils that are free to deflect under load. The coils at each end of the spring are inactive coils. If the spring coil at the end is cut in half, it is referred to as a half-inactive coil.
- Baking – This refers to the heating of electroplated springs to relieve hydrogen embrittlement. This is one of many stress relieving heat treatments which are designed to refine the grain size and improve the uniformity of microstructure properties in steel. Tempering is used to reduce the brittleness of the material.
- Closed and Ground Ends – Closed End spring, in which the first and last coil are ground to provide a flat bearing surface.
- Deflection – Deflection is simply the motion imparted to a spring by application, or removal, of an external load.
- Elastic Limit – Maximum stress or force per unit area within a solid material that can arise before the onset of permanent deformation.
- Free Length – The overall length of a spring which is not under load.
- Hysteresis – Mechanical energy loss occurring during loading and unloading of a spring within the elastic range, illustrated by the area between load deflection curves.
- Initial Tension – A force that tends to keep coils of a close wound extension spring closed and which must be overcome before the coils start to open.
- Loops – Formed ends with minimal gaps at the ends of extension springs.
- Mean Diameter – The average diameter of the mass of spring material, equal to one-half the sum of the outside and inside diameters. In a helical spring, this is equivalent to the outside diameter minus one-wire diameter.
- Natural Frequency – Lowest inherent rate of free vibration of a spring vibrating between its own ends.
- Pitch – The distance from center-to-center of wire in adjacent coils of an open wound spring. Also known as Coils-per-Inch.
- Rate – Spring gradient, or change in the load per unit of deflection.
- Spring Index – Ratio of mean diameter to wire diameter.
- Total Number of Coils – The sum of the number of active and inactive coils in a spring body.
A full list of spring-related terms and phrases can be found on Hyperco’s site under the Glossary tab in Technical Information.