The Ultimate Torsion Spring Guide: How to Measure the Spring Rate

Torsion springs are the primary dynamic loads in a suspension system. Their functionality is directly related to how they are measured, their spring rate, and the torsion spring capacity. A torsion spring can be thought of as a seesaw with two pivoting arms. One arm is fixed at one end and the other end of each arm is bolted to the chassis of the vehicle. When under load, such as acceleration or climbing a hill, one arm will twist more than the other and unload faster than its counterpart. This results in a twisting motion that we see as left or right-leaning of the vehicle body when viewed from behind. Boynes Springs is a torsion spring manufacturer in Australia that can supply springs for any application.

What is Torsion Spring Capacity?

Capacity is the maximum amount of torque (twisting force) that the spring can withstand before it breaks. Capacity is measured in tons. In an automotive context, the term “torsion spring” refers to a helical spring that is twisted when the car’s axle is turned. Its “capacity” is determined by how much torque it can handle before it breaks. A torsion spring’s capacity (or break strength) is measured when the spring is completely twisted in one direction to the point where it is at its maximum length from rest. 

How to Measure Torsion Spring Rate?

When measuring a torsion spring, the spring rate can be calculated by measuring the spring uncoiling rate. The spring uncoiling rate is the amount of time that the spring requires to travel from fully compressed to fully extended. When measuring a spring, it is important to make sure it is completely uncoiled and sitting at rest before beginning the timer. Once the timer is started, the spring will begin to uncoil. The spring uncoiling rate can be calculated by measuring the time it takes for the spring to travel between two fixed points. One end of the spring is fixed to a stationary object using a spring clamp and the other end of the spring has a stop attached to it.

Standard Torsion Spring Ratings

Torsion spring capacity ratings vary by the material of the spring, the diameter of the wire, and the number of leaves contained within the spring. Torsion spring capacity ratings are based on a vernier scale. This means that the rating is determined by how many full revolutions the scale has. For example, a 6x12x10 spring is rated for 6 full revolutions with 10 leaves. The most common types of torsion spring materials are wire and synthetic. Wire torsion springs are most commonly found in leaf-sprung vehicles. They consist of a helix of steel wire wrapped into a cylinder that is then coiled up to create the spring. Typically, wire torsion springs have a maximum rating of 80,000 lbs (36287.39 kg). They are the most common type of spring used for leaf-sprung vehicles.

Determining Actual Torsion Spring Capacity

When using a new torsion spring, you will want to start out with a lower capacity than the spring rating. The reason being a new spring has a greater amount of spring rate when compared to a used spring. The spring rate is directly related to how much coil stretch the spring has taken. The amount of coil stretch the spring has taken is directly related to how much the spring has been used. The easiest way to determine the amount of coil stretch is by measuring the length of the spring. If you take the new spring length and compare it to the used spring length, you will be able to get a good idea of the amount of coil stretch.

Finding the Ideal Torsion Spring for your Suspension System

A good rule of thumb is to start with a torsion spring that is rated for 20% less than the original spring rating. When choosing a spring you will want to pay attention to the spring rate. You do not want to choose a spring rated for a higher rate than the original spring. Doing so will cause the spring to be wound beyond its capacity and could lead to an early failure of the spring. With that being said, you do not want to choose a spring with less spring rate than the original spring either. Choosing a spring rated for a lower rate will cause the spring to be wound less than the spring that came on the car. This will cause the overall ride quality to be stiffer than the original spring. If in doubt, Boynes Springs is an expert when it comes to torsion spring capacity and can help you find exactly what you need.

Custom Torsion Springs Manufacturer in Australia

When you are looking for torsion springs, Boynes Springs is a trusted torsion spring supplier in Australia to help you with your project needs.  Get in touch with one of our spring experts today and upload your specifications sheet here.