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4x4 Suspension Basics - Common Knowledge

Coil Spring Suspension
Christian Lee | Writer
Posted February 1, 2011
Photographers: Kevin Blumer

The Need To Know On How To Lift

You didn't learn to drive without some basic fundamental knowledge, so why would you attempt to lift your 4x4 without at least knowing some 4x4 suspension basics? Take a peek at the following information to increase your suspension knowledge base, so you can weigh your options and lift your 4x4 with confidence.

Coil Springs
Coil springs will offer the best pavement ride when set up properly and can also handle trail use with ease. Coil-spring suspensions use a coil spring at each corner of a vehicle with link arms in place to act as pivots. Most production setups use two-to-four link arms, not including the track bar, which is often included in the count.

Made from a round bar of steel that is twisted in to a spiral shape, coil springs can be made with a constant or variable spring rate. The strength of a coil spring depends on diameter and length of the round steel bar, the number of coils, and the diameter of the finished coil. While coil springs are inexpensive to manufacture compared to leaf springs, their set up requires more labor and parts since they do not incorporate attachment points. Coil springs also feature different types of ends depending on their application.

One of the first 4x4s to use a coil-spring suspension was the '66-to-'77 Ford Bronco. Its front radius arm arrangement used coil springs and bent radius arms with the lower front shock mounts securing to the arms. With its front track bar helping to locate the axle it can be considered a three-link radius arm system. Many aftermarket kits are available to help early radius arm Broncos fit larger tires and increase flex.

In 1984 Jeep incorporated a similar design for the Cherokee, with its front four-link coil system. The Jeep Grand Cherokee and Wrangler TJ took the concept to the next level by adding the same coil setup to the front and rear. Jeep called it Quadra-Coil Suspension and it worked pretty darn well. Some of the available aftermarket long-arm lift kits for TJs, such as the Rubicon Express system, are actually radius arm systems since the upper front arms secure to the lower arms.

Combined with an independent front suspension many Toyota 4x4s, such as early '90s 4Runners, employ use of a rear four-link coil-suspension arrangement. This setup replaced the leaf spring rear that was previously in place on IFS Toyotas.

Leaf Springs
Leaf-spring suspension is the easy-peasy of the suspension world. It's easy to set up, it's easy to maintain, it's easy to lift, it's durable...it just requires less parts and less worry than other types of suspension systems. It's also one of the oldest suspension styles, having been put to use on wagons and farming and battle implements dating back to medieval times.

As seemingly easy as they are, however, leaf-spring suspension systems can still be set up incorrectly if the spring isn't matched to the weight of the vehicle or if too tall or too short a spring is used. Remember, not all leaf springs are created equal. There are many styles and options to choose from beyond lift size and spring rate, including spring eye type (standard, Berlin, reverse, reverse military), bushing type (steel-encased rubber or urethane), and how the leaf ends are finished (square, diamond point, or rolled).

Multi-leaf spring packs, also called semi-elliptical spring packs, are the most popular style of leaf spring. It's what you see on most 4x4s that don't use coil springs. Multi-leaf spring packs aren't just a bunch of spring leafs from a scrap pile clamped to a main leaf. A lot goes in to the design of a leaf spring and every facet of its design can affect a spring's performance. The number of spring leaves, types of spring leaves, length and rate of the springs, how they are stacked, the placement of rebound clips, and type of spring eye all come in to play in the design of a leaf spring. A well-designed leaf spring will not only function properly but it will last a while.

Mono-leaf springs are simply a single leaf spring that is thick in the center and tapers down to the spring eyes. It mounts the same way a multi-leaf pack does with spring eyes to the frame and a spring plate and U-bolts to the axle. Mono-leaf springs can work well for dedicated trail machines, but we're leery of their safety for highway use. If you break a leaf with a multi-leaf pack you can typically drive home on it. With a broken mono-leaf you have nothing left to support the weight of the vehicle and could be looking at some serious damage, especially at highway speed.

Quarter-elliptical spring packs look like a leaf spring cut in half. The spring eye end typically mounts to the axle while the leaf pack end is fixed to the frame. It works kind of like a swimming pool diving board allowing the axle to pivot up and down as the leaf spring compresses and rebounds. While quarter-elliptic leaf spring setups can work very well mounting is more difficult than a standard semi-elliptical arrangement. Most quarter-elliptical setups we see are on more custom 4x4s.

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