Fit My 4x4

Moment with Mic: Fitting Uprated Springs with Standard Shocks & Vice Versa

I often get asked if it is necessary to fit up rated shock absorbers when fitting up rated springs if the vehicle is still new and the original shocks would therefore also still be new.

We have previously discussed the function of the shock absorber or damper and the important relationship between the spring rate or spring stiffness and the shock absorber dampening rates.

The suspension engineer designs these two components to work together to provide a comfortable, safe and functional ride for the vehicle. Many aftermarket suspension companies supply what they call “matched kits”.

So what happens when you fit uprated springs to a new 4wd vehicle and keep the original shocks? For a start, there is going to be a mismatch between the spring rates of the uprated spring and the dampening rates of the standard shock absorber. The uprated spring is going to make the standard shock absorber work a lot harder and it will not be able to exercise the necessary control over the uprated spring. Without effectively controlling the spring oscillation, you will have an uncomfortable ride and, more importantly, a 4wd vehicle with bad handling. I do not need to tell you the dangers involved here. With the shock absorber now working near maximum most of the time, it will not last very long and you will need to replace it pretty soon in any event.

In most cases, fitting uprated springs induces a lift in ride height. Raising a 4wd’s ride height to enhance the vehicle’s ability to traverse rough terrain or to accommodate larger wheels and tyres is one of the primary reasons for a suspension upgrade. All suspension designs have fixed compression and droop limits. Compression limits are normally in the form of a bump stop rubber and the droop limit may be a similar droop stop rubber or in some cases it may be determined by the length of the shock absorber.

On independent suspension setups, raising the ride height generally has a negative effect on the vehicles ability to keep all 4 wheels on the ground during extreme suspension articulation. Fitting raised springs results in a ride height that is closer to the droop limit which causes that wheel to hang off the ground more readily equating to a loss in traction. It is very important to note that fitting longer shocks to independent suspension setups is not advised. Exceeding the droop limit may result in the failure of suspension components such as ball joints.

On non-independent suspension setups, the picture is slightly different. The droop limit is generally determined by the length of the shock absorber. Fitting longer shocks will extend the droop limit keeping the wheels on the ground more readily during extreme articulation. While the idea is simple, there are a few things to keep in mind. On coil sprung solid axles, the shock absorbers must not be too long so as to allow the springs to become unseated under full droop. One also needs to take note of brake line lengths and other components when exceeding the droop limit. Keeping the standard length original shocks on raised solid axle suspensions will of course work against this enhancement.

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