What's The Difference Between Upper & Lower Control Arms?

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Take control of your Mustang's handling and replace the weak and flexible stock control arms with a performance minded aftermarket set. Fine-tuning your Mustang's suspension is made easy with the quick to install, bolt-on performance options for both upper and lower control arms.
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What's The Difference Between a Mustang's Upper & Lower Control Arms?

Stock Mustang GT Upper Control Arm Stock '01 GT Upper Control Arm

The upper control arms keep the rear axle from moving side to side. They also eliminate any pinion angle deflection that can botch traction. The lower control restrains the rear axle from moving front and back, just as the leaf springs on older model vehicles and most trucks, the lower control arms transmit the force from the wheels to the chassis. Of course, the four-link system is much lighter, and more effective in preventing axle wrap than the traditional leaf spring set up.


For those who don’t know, axle wrap is Torque and traction combining to twist the axle, pushing the nose of the differential up going forward and down going backward) by twisting the axle into an "S" shape. The energy is stored in the spring until the tire slips, and at that point the spring snaps back violently. Sometimes this results in a hopping sensation, hence the other common term, "axle hop." It can be very hard on driveshafts and u-joints. Via Off-road Adventures

Installed Aftermarket Lower Control Arm Aftermarket Lower Control Arm

Weaknesses in a Mustang’s Stock Control Arms

Although a significant improvement over leaf springs, the four-link system has some downfalls in its stock form. Ford used a soft rubber bushing at the mounting points at the chassis and axle. This allows for a more comfortable, forgiving riding experience for the average driver but poor performance in the way of handling and traction.

 

The factory pieces are a stamped steel design and, along with the bushings, allow the suspension to be incredibly flexible. As one portion of the chassis moves upward, another part can move downward, which occurs during higher speed turns (body roll). This design leaves a lot to be desired in the rigidity area, allowing for wheel hop off the line and side-to-side movement of the axle during aggressive turns—all of which are not desirable, but can be corrected.

 

Choosing aftermarket Control Arms for Your Mustang

There are many aftermarket suspension options for today’s Mustang owner. Many of them are high quality tubular steel pieces with high-grade tig or mig welded seams, providing added rigidity and support. The tubular design is much more rigid than the stock stamped steel piece and in most cases, lighter.

 

A lot of the kits available are offered with solid polyurethane or spherical end bushings (spherical bushings allow for slightly better handling). Both of these are a huge improvement over the soft rubber stock bushings. The two most popular choices are adjustable and fixed control arms. Both can be used on a stock Mustang. However, if the car is lowered the adjustable control arms must be used to set the proper angle.

Stock vs Aftermarket Upper Control Arms Stock vs. Aftermarket Upper Control Arms

Should I Upgrade my Mustang's Control Arms?

Control arm upgrades are meant to maximize the handling characteristics of the Mustang by strengthening the car’s suspension components. This is achieved by utilizing stronger materials, as well as superior designs over the factory components. Obviously, there are different types of control arms, upper and lower, as well as fixed or adjustable to take into account when upgrading. Upgrading the control arms on your Mustang will help with traction and control by keeping your tires where they belong…on the ground.

The Downside to Aftermarket Mustang Control Arms

While increasing launching capability, there are a few downsides to be aware of. First, anything aftermarket isn’t free. Secondly, with a stiffer rear suspension the driver will feel some of those small road bumps and vibrations he or she never noticed before.

 

Installation Difficulty

 

Most mustang owners will find aftermarket control arms are quite easy to install. Basic hand tools, a jack, jack-stands and wheel chocks will handle the job. Most folks with basic mechanical understanding can tackle the install in a few hours time. The hardest part is removing those pesky stock bushings.

 

If straight line driving is the main goal, then the aftermarket control arms are the best option for mustang enthusiasts. They’ll reduce wheel hop and the wasted movement of axle rotation. If your more concerned with ride comfort and not feeling all of the bumps and potholes, sticking with stock might work for you.

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