Suspension

AJ Deysel explains spring rates and how to choose the correct one for you!

With all the suspension options and kits available nowadays, deciding which springs to fit to your 4WD is now harder than ever! Once you have decided on the height of your lift, getting a spring setup that will compliment your shocks and give you the best ride and off-road performance is sometimes a bit daunting.

There are really two basic categories of springs available on the market – linear springs and progressive (or variable rate) springs. Each type has different purposes and behaves a certain way.

Linear rate springs are the easiest to understand, they have a spring rate that is consistent along the entire length of the spring as it is compressed. When you think of a spring, this is typically what you are thinking of. As the load on the spring increases, the spring compresses an amount directly proportional to that load. So, if the spring is rated at 100lb per inch, it will compress 2in when 200lb is applied. In general, the most performance oriented springs are going to have a linear rate. The consistent nature of linear rate springs makes the car stable, optimizes traction, and makes the car more predictable for the driver.

Progressive springs on the other hand, have a spring rate that increases or changes with the compression of the spring. An easy way to tell progressive rate from linear rate springs visually is that a with a progressive spring, the amount of space between every winding, or coil, of the spring is different. As the spring is compressed, the soft coils on the tightly wound side will collapse, coming into contact with each other. When this happens, the rest of the spring starts to compress at the second higher rate. The theory is that this allows the car to travel smoothly over bumps and road imperfections but still be tight enough to provide good handling and prevent bottoming out. Because of this, these springs are popular for touring or social off-roading.

The downside to progressive springs is that they are hard to dampen effectively. A linear spring with a consistent rate is easy to match to a shock absorber, but a progressive spring will often go out of the effective damping range as it crosses into higher or lower rates. For use in road vehicles where the loads don’t vary much, progressive / taper wire or ‘flexy’ springs can be a good option, but for 4WDs that have different loading when going off-road, touring or playing on the weekend, the low initial rate is often maxed out and you are left driving constantly on the hard second rate which can often lead to spring failure or deformation over time.

So what factors should I consider for MY 4WD? Harder springs and softer dampening will be a firm ride with less body roll, where soft springs with harder dampening will also give a firm ride but with more body roll. Ride quality is often most critical when the wheel frequency and travel is fairly low. This is generally when a long soft spring with a low linear rate combined with appropriately valved shocks can provide a plush ride with smooth controlled dampening, and will allow the swaybar to handle body roll.

The majority of spring manufacturers provide springs that are often designed around OE length shocks or aftermarket shocks that really only have minimal increase in travel. By fitting premium shocks that are specifically designed not only for the vehicle but for the lift and all of the associated componentry, there is now the opportunity to fit much longer units which are held captive between the mounts. Always search for a manufacturer that can provide springs rated for the loads that your vehicle will carry and also provide the right amount of lift that is needed whilst taking into account the overall shock travel you are planning on running!

There is no point in having shiny new long travel shocks if they sell you springs that are so stiff you can never compress them. Spring material, scragging, coating and finishing processes are key factors to a long lasting quality off-road spring.

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