Long-Arm Vs. Short-Arm SuspensionPosted in How To: Suspension Brakes on August 1, 2010 Comment (0)
The debate over long-arm versus short-arm suspension is a seemingly never-ending bench race that centers on the pros and cons of suspension control arm lengths. While modern link suspension systems have expanded the off-road potential for many 4x4 vehicles, the control arm itself has been around for quite some time. From the first radius-armed Bronco in the mid '60s to the current five-link under the new Jeep Wrangler JK, control arms continue to breed innovation and performance into the industry.
Since most of us don't leave our rig's suspension untouched, the control arm is a hot item in the aftermarket world. Though most of the control arm debate has centered on the Jeep brand, the topic extends far beyond Mopar. With the reemergence of the radius arm under the new Ford 3/4- and 1-ton trucks and the fast-growing long-travel IFS market, plenty of fresh technology is stirring life into the control arm debate.
So what's so important about the control arm anyway? For many off-roaders it's all about suspension travel, increased stability, and vehicle control. While more travel equals greater traction and performance, the increased stability and control equate to a safer vehicle both on the road and off. Though we're definitely not going to end the debate here, we do have a few bench racing topics that should help those new to the link world join in the conversation.
A common misconception about longer control arms is that they automatically net you more travel. While a longer control arm may allow the suspension to cycle more freely, the shock absorber generally remains the part of the suspension that determines the vertical wheel travel. So if you have a 10-inch-travel shock on your short-arm kit and you moved up to a long-arm kit, but kept the same shocks, you still only have 10 inches of travel. The exception to this rule is if the shorter control arm system binds during travel, thus not allowing the shock to fully extend.
Long-arm upgrades are a wildly popular, and for good reason. Placing longer control arms under your rig helps to reduce the operating angles of the control arms once the rig is lifted. Longer control arms will also help smooth out the ride, increase travel potential, and reduce stress on the vehicle and its suspension components. Since we're big fans of keeping our rigs low, we like high clearance and arched long-arm systems to help improve ground clearance.
The rule about control arm angles is that the flatter they are the better. As the control arm strays from the horizontal plane it changes the geometry of the suspension. Extreme control arm angles are often harder on your suspension's components and may present a harsh ride, poor handling, and limited suspension travel. A short control arm coupled with an intense operating angle will have the less range of motion versus a longer arm placed at less of an angle.
Wristed radius arms have been used in the Ford stable for decades. From the Twin Traction Beam axles to the early- and late-model solid-axle 4x4s, radius arms are a simple and effective way to control the front axle. Upgrading to a longer radius arm allows the suspension to articulate more freely. Essentially the farther you space the arm's mounting point on the frame from the axle, the less dramatic the bushing bind will be as the suspension cycles.
When determining control arm lengths you must factor in axle sweep, pinion angle, and roll center. The mounting locations of the arms and the correlation between the upper and lower arm lengths play a major role in how the suspension performs. For example, if the upper control arms are drastically shorter than the lower ones, the axle may steer during articulation and could allow for extreme pinion angle changes that may result in drivetrain damage.
Another type of control arm that is gaining popularity is the long-travel A-arm. These long-travel independent suspension setups can easily net upwards of 15 inches of vertical wheel travel and have allowed OEMs like Ford and Dodge to produce durable long-travel 4x4s like the Raptor and Ram Runner.
Control arm mounts are just as important as the arms themselves. When you increase the operating angle of the control arm it puts force on the control arm mount in a way OEs didn't intend. This consistent change of force can damage the mount severely. We've seen quite a few factory suspension mounts peel off frames over the years. Often suspension kits will provide reinforcing brackets to help beef up the factory mounts.