Spring Rate

Spring Rate

To figure out the Spring Rate you start by compressing the spring about 20% of the available distance of the spring and measure the height (Load Length 1) and the Load 1 in (lbs/inch) or (N/mm). Then compress the spring about 80% and measure the height (Load Length 2) and the Load 2

                                  (Load 2 - Load 1)
Spring Rate = -------------------------------------------
                       (Load Length 1 - Load Length 2)

Most springs are fairly linear, which means you would get the same Spring Rate from the equation no matter which distances you would use, 20% and 80% as shown above, or 40% and 90%, or 10% and 30%.

Some springs are non-linear, which typically means the spring gets stiffer the more you compress it.  One way this can be done is by changing the coil spacing, so that coils start to touch each other as you compress it.  Another way common in racing is for the spring to compress and then encounter an additional spring.  This increases the spring rate because now you have 2 springs acting on the force.  Many times this additional spring is a rubber "bump stop".

Most vehicle springs are coils.  Torsion bars are another style, and are basically a coil spring straightened out.  Leaf springs are different than both in that they have some built in dampening (shock absorber) due to friction leafs rubbing on each other.  

What affects Spring Rate

There are 3 primary variables that affect Spring Rate

1. Wire Diameter: When the diameter of the wire increases so does the Spring Rate. When the wire is thicker it becomes stronger and more difficult to deflect.

2. Spring Diameter: When the diameter of the spring increases the Spring Rate decreases.

3. The number of coils in the Spring: As the number of coils increase the spring rate decreases.

Programs that work with Spring Rate

Our programs work with 2 basic applications of springs, suspension springs and engine valve springs.

Suspension Springs:

We have 5 programs that work with Spring Rate when conducting Suspension Simulation. Roll Center Calculator v3.6 works with the front Spring Rate only. Roll Center Calculator Plus v3.6 and Circle Track Analyzer v3.6 work with and can calculate Spring Rate of the front and REAR of vehicles.  

Our Suspension Analyzer v2.4 program is our top of the line Suspension Program and works with Spring Rate with more precise 3D (X, Y and Z coordinates) inputs so you can design your suspension to perform the way you want. And our Suspension Analyzer Full Vehicle v2.4. also work with Spring Rate of the rear suspension.

And Circle Track Log Book v1.1 allows you to document your vehicles setup for a given track or track conditions. You can record the Spring Rate of both the front and rear suspensions for future analysis.

Valve Springs: