Extra weight? Don’t shed it, learn how to choose springs for loaded off-road vehicle
When you become the proud owner of an off-road vehicle, one thing is certain: it won’t be long before you start making modifications. After all, there’s a reason you chose this type of car. If you’re not already a passionate fan of off-roading, perhaps you’re planning a trip. However, 4×4 travel is not easy, especially for vehicles. It involves a lot of extra weight that the factory suspension isn’t designed to handle. The springs supports this the most, so it’s important to learn how to choose the right springs for your vehicle’s weight.
Weight distribution in the vehicle – what you need to consider
If you’ve ever seen an off-road vehicle designed for traveling, you know how serious weight distribution is. These vehicles often look less like cars and more like mobile homes. A roof rack with a tent might be mounted on the roof, custom storage in the trunk, a solid bumper with a winch at the front, and a spare tire at the back. This is just an example of permanent extra weight that can accumulate in the vehicle. On top of that, you need to consider the cargo, especially in pick-up trucks, which are designed for carrying loads.
When calculating the distribution of the vehicle’s extra permanent weight, you need to consider not only the front and rear axles but also the center of the vehicle. The goal is to balance the weight from this point proportionally between the front and rear, depending on the roof’s placement. In off-road vehicles, where the roof often extends further toward the back, you can simplify this by assuming 40% of the weight is allocated to the front and 60% to the rear.
The placement of individual accessories will also impact how the added weight is distributed. For example, a spare tire on the rear door, like on a Jeep, places more weight on the rear than a trunk itself. Moreover, the type of engine you have also affects the final weight of your off-road vehicle. Diesel engines generally weigh more than gasoline engines.
Springs for a loaded off-road vehicle – how to choose based on weight
The key factor in choosing springs based on vehicle weight is their stiffness. More weight causes the body or frame to sag more on each axle, which reduces the suspension’s range of motion, leading to poorer handling. Stiffer springs will help stabilize a heavier vehicle, making off-road driving smoother. You can learn whether your vehicle is properly leveled by reading the section on how to measure suspension lift height.
Matching springs to the vehicle’s weight is relatively easy, as suspension parts manufacturers provide weight ranges for their springs. These ranges refer to non-factory, additional weight. For example, you might find springs for:
- front:
do 30 kg
30– 60 kg
50– 80 kg
50– 100 kg
- rear:
0– 100 kg
0– 300 kg
250– 500 kg
100– 250 kg
Some manufacturers also provide constant load values, such as “250 kg constant load” (constant weight meaning additional load). This isn’t a perfect match since it’s set within a certain range. So, 50 kg more or less won’t make much difference, but 100 kg less can result in a slightly higher lift and a stiffer spring.
Another important point is that you can replace springs in pairs rather than replacing the entire set. So, if you’re adding weight only to the front of the vehicle, install new springs on that axle. If you’re wondering whether the type of progressive spring or linear spring affects its maximum load capacity, the answer is no. Regardless of the winding characteristics, the most important thing is the values given in the specifications.
Too stiff isn’t good either
Don’t make the mistake by buying stiffer springs “just in case” for the future, that might never happen. Only consider this option if you’re sure that the weight of your off-road vehicle will significantly increase soon. Always match the spring’s maximum load capacity to the vehicle’s current weight. Otherwise, your suspension will be too stiff, and the wheels will bounce on every bump, throwing you out of your seat.
If one axle sags more than the other despite choosing the correct spring, you can use a leveling kit or select a higher spring to compensate for the difference.
Spring rate – the truth about stiffness
If you have some springs in your garage or workshop and aren’t sure if they’ll handle the new weight of your vehicle, you can calculate it yourself using the spring rate. The spring rate measures stiffness by indicating how much weight (in pounds) is needed to compress the spring by one inch. Factors that affect the spring rate include:
- Wire diameter and winding type
- Number of active coils and total number of coils
- Free length – the height of the spring when no force is applied
- Outer and inner diameter
Once you have all these values, the easiest way to calculate it is by using dedicated calculators often found on manufacturers’ websites.
About leaf springs – not just springs for a loaded off-road vehicle
We mentioned pick-up trucks earlier, so it’s important to talk about leaf springs as well. In this case, it’s a bit simpler since the weight range for the maximum load is much higher than for springs. For example, leaf springs can support up to 500 kg of additional weight. Why the difference? Simply put, leaf springs are structurally much stiffer, less flexible, and designed to carry heavier loads.
If you need to increase the load capacity of the leaf springs, you could theoretically add an extra leaf. However, this isn’t the most cost-effective investment. First, an extra leaf isn’t much cheaper than a complete leaf spring replacement. Second, this method won’t provide a lift higher than 1″, which is important if you’re installing a large vehicle setup.
Klaudia Kusy
Author of the article
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