Jeep Wrangler Coils Explained

Leaf spring suspension is among the oldest form of suspension design. A series of steel plates are staggered and braced together to form an arc. The arc is positioned below the axle and both ends attached to the frame.  The main advantage of a leaf spring suspension is its simplicity. Very little can go wrong and it's fairly inexpensive to fix or replace. They are also easier and cheaper to upgrade in terms of a lift modification. Leaf springs are also much sturdier and used in heavier more demanding trucking applications. The disadvantage of a leaf spring is its fixed state, this doesn’t allow for much geometry correction to help aid in handling. They also have less travel and ability to articulate while keeping wheel contact. This can become problematic in off-road conditions.

A coil based suspension offers more versatility and geometry adjustment, allowing you to correct any handling issues. Coil suspensions also offer more room for travel, which is a benefit while on the trail to ensure more contact with the ground. They are more expensive to maintain and upgrade but the advantages out-weigh the negatives. For modern off-road applications and coil based suspension is almost always a better option.

Thanks to manufacturing advancements, the world of coil springs has significantly evolved through the years. We’ll take a look at the three major types and discuss the benefits and disadvantages of each.

These are the most basic type of springs found in modern vehicles on the road today. These are the same springs that modern Jeeps come equipped with from the factory. It is also among the cheapest options in terms of replacement or upgrade. They offer a consist entry level of performance and in most cases enough for your application. Entry-level suspension lifts, including leveling kits, use linear springs because they are inexpensive to produce. Dialing in a specific coil rate, during manufacturing, ensures a constant level of ride firmness. A linear spring works by completely compressing in an even rate throughout the length of the spring.

As a result the ride firmness is consistent and the same, no matter the speed or conditions. For off-road use, one of the main drawbacks with linear springs is suspension travel. The overall length of a linear spring is smaller than other options. This limits the amount of travel/articulation while a Wrangler is capable of off road. Another major drawback with linear springs is “Sagging”, this is when the spring, through time and use, becomes fatigued and over-worked. It can no longer sustain the same level of height and slowly loses its firmness, resulting in loss of height and performance. Linear springs are also very difficult to estimate lift height because of the effects of weight and pressure being applied by the vehicle. Manufacturers often provide a “Fully Loaded” weight estimate when assigning a number to lift kits. These estimates can increase tremendously with linear springs. Suddenly an estimated 2.5” lift can turn into a 4.5” actual lift on an otherwise stock Wrangler. These wild variables make it difficult to properly adjust the Wranglers suspension geometry and could lead to problems with handling and driveshaft rubbing.

These springs offer a big improvement in ride height and performance by offering a steady increase in spring rate throughout the length of the spring. The top half will start at a lower rate and then progress in rate throughout the rest of the length.

This allows for more resistance to pressure and adaptability to road conditions and use. The faster the vehicle is traveling and the more active the suspension, the stiffer the suspension will get as it engages the stiffer rate portion of the spring. The slower and less active the suspension movement will result in a softer ride as only the lower rate is being used. This allows the functionality of a varying suspension firmness when on and off road and city to highway driving. One of the drawbacks of progressive springs is the price. They are more expensive and are typically found on higher-level kits. Although not as bad as linear, progressive springs are also prone to sagging over time since the entire spring is always engaged and the last two coils tend to take the brunt of the force from compression.

These springs are just starting to emerge as an alternative to progressive springs. The best way to understand dual rates is to imagine two independent springs, each with their own rate of firmness, fused together. The top sets of coils have a very relaxed firmness that supports the weight of the vehicle. The bottom half provide the actual performance.

This allows for a more consistent ride height. However, the biggest advantage that dual rate springs have is more travel. Relaxed they are a taller spring, this allows for more suspension travel and greater articulation, by maintaining constant engagement. Also, the bottom portion of the springs is active during travel. This engages several coils, ensuring a reliable and consistent level of performance and height. It also addresses the issues of sagging over time by not overworking the bottom coils and using the dual rate disbursement to properly handle the static weight and road force independently. A negative for dual rate springs is cost. They cost significantly more to manufacture and as a result cost more to purchase. They are typically found as an option for higher-end kits but could easily be integrated with lower level starter kits. Because the ride height is so predictable many of the geometry and drive shaft issues caused by unexpected increases in actual lift amount are non-existent. Dual rate springs are still an emerging option and are only carried by a few companies, making exclusivity and sourcing a problem.

The overall decision on the type of spring to choose largely depends on budget and use. For a low budget, entry-level option on vehicles that will spend the majority of the time on the road and an occasional off road use, the linear spring at a firmer rate is enough of an upgrade from the factory spring. If you are looking for a better handling option than stock, a progressive spring offers a good variety in firmness while still providing the capability of off road travel. If you are in the market for a higher-end spring that provides the maximum amount of suspension travel and the benefits of better road handling a dual rate spring might be a better solution.