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Jeep Suspension - Four-Link Lingo

Posted in How To: Suspension Brakes on January 1, 2008 Comment (0)
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Exclusive Jeep Tech article which looks at Jeep suspensions, and the difference between a Four-Link Suspension and a Three-Link Suspension!

n. stepping up to a whopping even number of links is the four-link suspension. With four arms (two upper and two lower), eight links, and three common ways to design it, this is harder to dial in and more common than a three-link. See also: tri*an*gu*lated four-link; dou*ble-tri*an*gu*lated four-link; four-link with pan*hard bar.

n. this is the stock type of suspension found on the front and rear of TJs and ZJs, and the front of XJs and WJs. With four parallel or near parallel links or arms, there is no way to control the lateral motion of the axle under the Jeep. A panhard or track bar is introduced to the equation to control lateral movement.

n. these are the parts that control the location and movement of most modern solid-axle rigs. Whether it's three-link or four-link, if it's got solid axles and coil springs, you'll find arms underneath it. See also: links.

n. contrary to what the name implies, adjustable brackets usually aren't adjustable at all. They are normally a piece of steel with several holes drilled through it, which provides adjustability in mounting the links. This allows adjustment of squat, anti-squat, roll center, and instant center.

n. this is not what you do when the toilet seat is cold. By drawing a line from where the tire contacts the ground through instant center, you can determine antisquat. If that line intersects a line drawn perpendicular to the front axle above the center of gravity, you've got antisquat. This is designed into the four-link by varying the length and geometry of the links.

n. an imaginary point which is stationary relative to the Jeep and has very significant value. It's the average location of the weight of the Jeep, or the point around which the Jeep will balance. If this point goes past the perimeter of the Jeep (too steep a climb, or too off camber), you will roll.

n. fancy engineering term for the frame of the Jeep. A woman with a particularly nice form could be said to have a great chassis, also.

n. the point at which the rear suspension provides lift. It contributes to your squat and antisquat. It's an imaginary point, which moves as the suspension cycles. If you extend the upper and lower links when looking at the vehicle from the side, the point at which they converge is the instant center.

n. these are the most important components to a three- or four-link suspension. Without them you'd have a three or four suspension. Just how goofy would that be? See also: arms.

n. in a typical link suspension there are upper and lower links. Because you are constrained by your chassis and axle location, the lengths of the links are often limited. You can calculate out the ideal for your situation, but often you will just be back to whatever you can make fit.

n. also known as a panhard rod or track bar, this is the common fifth link in a four-link suspension setup. In a non-triangulated four-link, it's needed to keep the axle located under the Jeep. Very common on lifted Jeeps to rip this link off the axle due to the forces involved.

n. another imaginary line. This one is the line drawn from your front roll center to the rear roll center. Inclined roll axis contribute to roll steer.

n. the imaginary point that the axle will rotate around when flexing.

n. when your axle is articulating and causing your Jeep to steer, without steering input, this is said to be roll steer. For example, in the rear axle, as the tire drops, it travels forward and inward; as it rises it travels rearward and outward. Also known as flex steer and rear steer.

n. by drawing a line from the point of tire contact with the ground through the instant center, you can also determine squat. It's not a desirable result if the line drawn intersects the line drawn from the front axle below the center of gravity because it lessens the pressure on the contact patch.

n. in this configuration, both the upper and lower links are triangulated. This helps locate the axle (without panhard bar), as well as minimize flex steer throughout the axle's range of travel.

n. as the name indicates, it's got only three links, technically. In all actuality, it's much closer to a triangulated four-link than anything else. It's just got one joint in the center of the axle for the upper links. And because the two upper links are connected using one joint, it's called a three-link This style of suspension can be found under the rear of a WJ and KJ.


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