How to Set Proper Spring Preload on Coilovers

So you’ve bought a set of coilover shocks for your car with spring preload adjustment (or “spring tension”), but do you know how to set it up correctly? Maybe your coilover system doesn’t have a separate ride height adjustment, you set it to produce your desired ride height and now you just hope that the set preload is within the proper range. Or maybe your coilovers have a spring preload adjustment independent of ride height adjustability, but you’re not sure how this affects performance. In this article we will describe the effects of spring preload and how to set it correctly.

Having too much or too little spring tension will negatively affect suspension performance, but in different ways. Too much tension on the spring can make the suspension feel like it’s overflowing. This happens because now the shock is extended to its maximum length too suddenly, and this can unload your wheels from the road surface. Insufficient spring tension can cause the suspension to bottom out excessively. Knowing these effects can help you make the correct adjustments.

Let’s define some terms to help understand the effects of spring preload. The amount of travel the spring consumes at a static ride height of the vehicle’s weight is called the “drop.” And the amount of stroke left at a static ride height is called the “compression stroke.” The full shock stroke is combined with the drop and compression stroke.

Equation:

Total shock stroke = fall + compression stroke

It is important to understand that spring tension does not affect the spring speed of a linear spring (most coilover systems come with linear springs). For example, increasing the spring preload will NOT increase the firmness of your linear spring. However, this will increase the amount of compression stroke you have, which increases resistance when bottoming out.

The springs in most coilover systems must be preloaded to retain a desirable amount of compression stroke at a static ride height. For example; If you have a 200 lb / in spring rate coilover carrying 800 lbs of weight, without any preset spring preload, the coilover will compress 4 “just by the 800 lbs of static weight acting on it. 5 total “of stroke, this only leaves you with 1” of compression stroke to spare! In this scenario, you must preload the spring to ensure you have more than 1 “of compression stroke. There is too much fall in this scenario.

So now we know that the spring tension affects the drop. But what is the proper amount of drop? This varies based on the amount of total stroke your coilovers have, so we treat the desired drop as a proportion of the total shock stroke. To have an adequate amount of drop, we recommend setting the drop to 30-40% of the total shock stroke (see equation below). Now you know that you have to adjust the spring tension on your coilovers to produce a 30-40% drop!

Equation:

Desired Drop = Total Shock Stroke x.35

How to set the spring preload:

You must first measure the total shock travel of your coilover (including the length of the stopper). Next, measure how much the coilover compresses when the vehicle is at a static ride height. Subtract the compression stroke at a static ride height from the total crash stroke to find the amount of drop. Adjust spring preload until suspension sag is between 30-40% of full shock travel.

Equation:

Drop = Total Shock Stroke – Compression Stroke

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