What Is the Difference Between Variable-Rate and Constant-Rate Springs?

Posted on March 31, 2020 by IDC Spring

If the products you manufacture involve the use of springs, as so many do, you need to be very careful about the types of springs you use. Spring varieties operate very differently, and choosing the wrong spring for your applications could result in product failure or, at the very least, less than optimal functioning.

Springs are often categorized in two main ways: progressive or linear. Variable-rate is another term for progressive springs, while linear springs are sometimes called constant-rate. The type of spring you need for your mechanics depends on the variables you look for or need for their application. Many kinds of springs, like compression varieties, come in both linear and progressive forms. Choosing the correct type of spring for your project depends upon the force-deflection you need.

Graphic that explains the differences between linear and progressive springs.

What Are Linear or Constant-Rate Springs?

Compression springs are a type of linear spring, though they can come in multiple forms. When compression springs are linear, the coils are evenly spaced from each other. Compression springs are common in many industries, such as door locks, dock levelers, snowplows and more. Extension springs are also available in a linear format.

What Are Progressive or Variable-Rate Springs?

Progressive rate springs have uneven spaces between the coils, which is what differentiates them from a linear spring. Mini storage and other industries commonly use progressive coil springs for overhead doors. You can also use these products for agricultural equipment and trailers because they stiffen when compressed, which is beneficial for driving over bumps.

Variable-Rate Springs vs. Constant-Rate Springs

When we talk about variable rates and constant rates, we are referring to the rate of force acting upon the spring, or “deflection.” Constant-rate springs have a uniform rate of deflection because they are the same diameter from top to bottom. So, for example, a spring with a 200 pound-per-inch linear rate will compress one inch for every 200 pounds of load that is applied. This is true for the entire length of the spring, so after 600 pounds of load, for example, the spring will have compressed three inches.

A progressive spring does not have a constant rate of deflection. For this reason, they are called variable-rate springs. In these springs, there is not an equal distance between coils, so the rate of deflection increases as you compress the spring. This type of spring is very popular in vehicle suspensions. An advantage of this type of spring is that it can stiffen quickly, meaning it can easily absorb smaller force amounts, but it is also strong enough to handle large force loads. A disadvantage is that you need a longer progressive spring to get the same amount of total deflection as a linear compression spring is capable of.

When deciding what type of spring you need, it’s vital to consider the application. Linear or constant-rate springs deflect force at the same rate because they are designed with equal distances between the coils. With progressive or variable-rate springs, the rate of deflection changes during compression because the distance between the coils is uneven. 

Order the Linear or Progressive Springs You Need From IDC Spring Today

At IDC Spring, we have various springs to fit your needs. We have both linear and progressive springs available in torsion, compression, extension and barrel options.

We manufacture our springs from stainless steel, galvanized wire, oil-tempered wire and numerous other materials. You can custom order your springs to meet the exact specifications for your project.

17 out of 25 of the top manufacturers in the industry choose IDC Springs. We have three primary locations in the United States for regional service, and we also ship nationally.

You can contact us online today to learn more about our linear and progressive springs or request a free quote.