How to Avoid Suspension Sag in Trucks and Trailers?

You will notice a lot of trucks and trailers that have a slightly lower rear-end. The vehicle leans backward due to sagging rear suspension. You can attribute this to harsh ride, poor handling, and haggard springs. If you take a closer view you will understand that the driving style has a lot to do with it. Application of sudden brakes, poor steering control, improper loading of weight, the quality of the roads on which these trucks and trailers travel, the quality of the springs used all have a major role to play in sagging. It is not just the mechanical factors which count here, the gentleness with which you handle your trucks and trailers and the care you take to keep them in good condition help you to cut down costs.

Carrying heavy loads in your truck also causes the front or rear suspension to sag and deviate lower than expected in performance. To avoid sag, installation of powerful durable hollow rubber cushions will help in carrying the heaviest loads effortlessly without ripping-off the suspension.

Springs are designed to cope with extreme conditions like highway cruising to severe off-road use, whether the vehicle is laden or not. The springs are integrated with a correctly matched shock absorber and determine the optimum limits the suspension can withstand. A shock absorber controls the spring, dictates the ride quality, and is often used as a stop to limit sagging.

Ideal sag measurement is determined by various factors which vary from individual to individual, their abilities, riding styles, weight of the driver, and measuring techniques. The above factors should be taken into consideration before replacing the spring.

Attention to spring design eliminates ‘sag.’ Steps during the design and fitting stages will ensure no built-in failures occur. Leaf lengths are calculated to ensure that the spring is as uniformly stressed as possible. Inappropriate lengths will concentrate stress in one particular area and will cause premature sagging or breakage. Fitting a shock absorber and leaf or coil spring system will instantly result in improved towing capabilities, an increased load-carrying capability, enhanced off-road traction and excellent on-road comfort.

Suspension sag is of two types:

1. Static

2. Free

Static sag involves how much the suspension compresses under the weight of the rider and free sag involves how much compression occurs under the weight of the trucks and trailers alone.

Calculate the static sag and adjust the rear preload accordingly – one turn of preload usually equates to between two and three millimeters of sag. Here’s a tip to check your rear spring rate. Lift the rear end of your empty vehicle with the help of equipment, until the suspension tops out. Next, gently let it settle – how much it drops is the free sag, which should be approximately five millimeters. If the suspension doesn’t drop at all, you’ve overloaded your vehicle and should consider a stiffer spring.

Broadly thinking suspension sag is not always a bad thing, a correctly set up vehicle with evenly distributed weight will ride smoother, deal with imperfect roads, and reduce rider fatigue.

The bottom-line is to never load your trucks and trailers beyond the manufacturer’s gross vehicle weight rating.


You may not be mechanically inclined but a combination of common sense and basic knowledge of your truck is definitely a worthy investment. As a result, you may experience a smoother ride on your trucks and trailers and run farther with lower maintenance costs.

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