Jeep Wrangler Coil Overs Explained

A coil over is essentially a shock installed within a spring, forming a single suspension unit. Both the shock and spring are specially tuned to work together in order to achieve the best rebound and dampening performance for a given terrain. The shock body itself is typically filled with oil and has a shaft that runs through the center. The shaft has a piston with small holes and washers that are sometimes called shims. The holes and shims are designed to let the oil flow through and therefore offer some resistance that functions as the dampening mechanism for the shock. The shims are the main adjustable component of the shock and controls the rate at which the oil flows through.

In addition to oil, many high-performance shocks are also pre-filled with nitrogen. The nitrogen provides another element of pressure against the oil that also prevents air bubbles in the oil. The formation of air bubbles is called cavitation. Heat build-up during excessive or heavy use while on the trail can also create air bubbles. Excessive amount of air bubbles will quickly degrade the viscosity of the oil and overall performance of the shock. This is why most shocks have an aluminum body. The aluminum serves as a great heat displacement element, helping to keep the shock body and oil cool as well as to help keep everything operating at optimal temperatures. Some more sophisticated systems utilize reservoirs or piggy-back cylinders that provide more oil and gives the shaft and piston more travel. The transferring of oil between the reservoirs and main shock body allows the oil to maintain a more stable efficient temperature during heavy trail use.

In terms of dimensions, most coil overs are offered in a 2, 2-1.5 or 3-inch diameter shock body. The shaft typically has a travel amount from 6 to 18-inches. The most commonly used shock is 2-inches in diameter and has a travel length of 10 to 16-inches. A larger 3-inch shock body is designed for a higher level of oil capacity, which in turn helps keep the shock temperature cool, but in most cases that size shock isn’t necessary and could make the overall installation more difficult. In addition, due to the popularity of 2-inch coil overs, there are more spring rate choices available.

Regular suspension: The JK Wrangler comes from the factory equipped with four shocks and four springs as separate components. The shocks are bolted to the Jeep’s frame and lower mounts that are welded to the axles. The springs sit separately within perches sandwiched between the frame and the axle. When functioning properly, the spring absorbs the impact in the road and rebounds. The shock, in turn, dampens the energy from the spring and controls the force produced from the rebound. Both items work collectively but are installed independently.

Coil over suspension: As mentioned earlier, unlike a regular shock and spring, a coil over is a self-contained unit. The shock is installed in the spring, forming a singular component. Overall, it performs the same basic functions of a shock and spring by also absorbing and dampening impacts on the road. The difference, however, is the advantage of adjustability that the coil over system has over a separate shock and spring. By working as one unit, the coil over is much more predictable and easier to tune.

Coil overs also have a threaded outer body with adjustable spring perches that swivel around the threads to either compress or decompress the spring. This action of compression/decompression of the spring results in overall height adjustment of the Jeep, providing another key tunable element unique to coil overs when compared to standard suspensions. 

Considering the complexity and cost of most coil over suspensions, the aftermarket world is somewhat limited to a few key manufacturers. More affordable options and new manufacturers are becoming more common as time progresses. Overall, the market is still considered a niche segment with few choices.

Most systems currently available allow for height adjustments from 3.5” to 6”. It’s important to keep the height range in mind during installation. At a 3.5” of height, the system can run with little to no other suspension geometry modification. However, once the Jeep has been lifted over 4-inches, there are several important components that will need to be replaced/adjusted to correct the overall suspension geometry. In addition, some coil-over kits are referred to stage 2 and involve a much more involved overhaul of the Jeep’s frame and suspension. This, in turn, produces a stretched-out wheelbase for better articulation and overall suspension travel. These more complex kits are usually installed by trained mechanics and involve a higher labor rate.

Coil over kits also require more maintenance, especially in colder climates where the Jeep is exposed to snow and salt. The elements can work themselves into the threads of the shock body and sometimes seize the spring perches, preventing them from moving for any type of adjustment. Within those conditions, it’s always best practice to remove each coil over and fully disassemble for proper cleaning and maintenance several times a year. This level of up-keep can be problematic for some owners but is an important factor when considering coil overs.

Lastly, due to the complexity of the systems, most coil over kits are fairly expensive. With most kits starting at over $1,000, the systems can easily climb over $4,000 for the kit alone. This isn’t considering other suspension elements you might need to take full advantage of the benefits of a coil over kit. The price also doesn’t include installation which often times requires the help of a professional, bringing the overall cost of a coil over kit to a substantial investment.

As discussed throughout this information guide, coil overs offer tremendous benefits while on the trail, providing Jeep owners with a large range of tuning in height, firmness, and overall performance. This ability of customizations comes at a high financial price, more involved installation, and overall maintenance throughout the year. All important points to keep in mind when considering a coil over kit for your Wrangler.