Mustang Suspension Overview – Everything You Need to Know

Camber is the tire lean when viewed from the front of the car. The top of the tire can either lean in, lean out, or be perfectly vertical. At first, you might think a perfectly vertical orientation is preferred, but that's only the case on flat tracks.

A little negative camber can enhance your Mustang's cornering ability, allowing the outside tire to grip better in the corner since the lower side of the tire will tend to try and roll under as it turns.

Positive camber is when the upper end of the tire leans out further than the bottom. Positive camber should be avoided, as it is detrimental to handling in nearly all cases.

Zero camber is when the wheel and tire are perfectly straight, vertically.

As you lower your Mustang, you also create negative camber on the front wheels. If left out of spec, expect reduced tire life. In some cases, a trip to the alignment shop will preserve your tires. The more lowering involved, however, the greater the chance you’ll need to enlist the help of camber plates for your front shock towers.

Caster is the relationship between the steering axis and a true vertical position. For the Mustang, the steering axis is the strut. A higher caster angle gives a car more stability at higher speeds. Although at slower speeds, the steering will feel heavier. Caster can also enhance the camber angle as the wheel is turned, giving you more grip in a turn. 

Toe angle is how the tires point when looking at them from a bird’s eye perspective. Toe-in has the two tires pointing slightly towards the center of the car, while toe-out has them pointing away from center. A slight amount of toe-in helps higher speed stability since the wheels will toe-out slightly as speeds increase.

Older Mustangs (Foxbody up to about New Edge) tend to suffer from toe-in while turning. Aftermarket K-members tend to help prevent this, but it's quite the time sink. Only consider a K-member if you're willing to change out 90% of your Mustang's suspension.

An alignment refers to a procedure that alters the camber, caster, and toe angle to make sure the vehicle is set correctly. What is considered "correct" refers to factory specs, but in the event you have a race-prepped Mustang, some more aggressive settings enhance suspension performance.

Camber and caster are set at the front shock tower or the strut itself. Toe is adjusted via the steering tie rods. While you can alter the alignment at home, it's best to take it to a shop that can accurately measure your Mustang's front suspension adjustments.

Although the top of your front shock towers allows you to adjust the vehicle's camber, you'll likely find the adjustability is minimal. Especially true with lowered cars, there may simply not be enough adjustability to bring everything back into spec. Even some factory Mustangs prior to 2005 can have trouble returning to spec with the available adjustments.

This is where caster/camber plates come in. They give you a much greater range of adjustability for camber, while also able to tweak your caster angle. All in all, you’re looking at a more balanced front end with the possibility of improving turning radius (depending on how much you tweak the caster). Whether you're looking to enhance your vehicle's cornering ability, or bring it back into spec, a set of caster/camber plates is a worthwhile investment. Pairing a set of caster/camber plates with an aftermarket K-member will provide the most adjustment for caster.

The Mustang uses a chassis with two main components, the front and rear subframe. While the two sections are connected by the floor pan, this is nothing more than sheet metal. The actual frame rails are not connected. While the rest of the car's body provides some rigidity, there can be unwanted flex when you stress the chassis. This stress can be a result of hard cornering or dragstrip launches. The solution for this is simple, and can be found in the form of subframe connectors which will tie the front and rear subframes together, thus stiffening the chassis.

• Bolt-on subframe connectors offer easier installation
• Welded connectors provide more stiffness than bolt-ons
• Strut tower braces reduce body flex in a different way than subframe connectors
• Some strut braces clear superchargers
• Rear shock braces are a minor upgrade but still reduce flex. Usually requires welding
• Torque box braces dampen the force of hard launches
• A full roll cage offers the most rigidity

There are a variety of suspension components controlling how your Mustang handles:

• Ball joints
• Bump steer kits 
• Control arms (Not applicable to S550 Mustangs)
• Sway bars
• Shocks and struts
• Springs
• Strut and shock tower braces
• Panhard bar (Not applicable to S550 Mustangs)
• Vertical links (S550 only)
• Toe rods (S550 only)
• IRS bushings (S550 only)

With all of the above coming standard on your Mustang, there are a good bit of aftermarket add-ons that either replace an existing component or are a completely new addition. These include:

• Air lift suspension kits (replaces shocks, struts, and springs)
• Coil over kits (replaces shocks, struts, and springs)
• Watts Link kits (replaces panhard bars)
• Caster camber kits

The late model Mustang's front suspension tends to be a bit more complicated than the rear, due to the steering rack and associated components. From 1997 until 2004, struts and springs were mounted separately with the spring closer to the engine. Beginning in 2005, the springs were mounted over the front struts up in the top of the wheel well. The wheel’s spindle is mounted to the control arm, providing a point to mount the wheel and tire. A sway bar is used to connect the two control arms together to control body roll.

Up until 2004, the late model Mustang's rear suspension used a four-link setup. Two upper and two lower control arms hold the rear axle in place, giving the suspension its four-link moniker. Springs support the rear of the car, above the axle, with separate shocks installed to control the dampening. The main issue with this suspension type is how the control arms are mounted. Instead of running parallel to each other, they're tilted slightly out. Combine this with Ford making their pony understeer like all hell, but when ran hard will snap steer. There are reasons why control arms, K-members, and more are on a bunch of wish lists.

Depending upon whether your Mustang is a V6 or V8, it has a 7.5 or an 8.8 inch rear end. The 7.5 uses an open differential while the GT's 8.8 inch rear end uses Ford's Traction-Lok differential. The 8.8 inch rear end was also equipped with quad-shocks during these years which help dampen the axle and reduce wheel hop. A sway bar is installed on both versions of the rear end to help control body roll.

The rear suspension underwent a significant change in the 2005 model year in terms of how the rear axle is positioned under the car. The four-link suspension setup was nixed in favor of a three-link panhard bar setup, a compromise between a full independent rear suspension and a solid axle. A 3-link setup includes (2) lower control arms, but only (1) upper control arm.

An independent rear suspension would have added a substantial cost to the initial price of the Mustang. In addition, many Mustang enthusiasts prefer a solid rear axle anyway, as it's more suitable for dragstrip duties The panhard bar setup preserves the solid axle while providing cornering ability improvements that suit most owners better than previous Mustang generations. 

IRS setups allow both rear wheels to function and move independently of the other. This allows for greater control and handling. In IRS setups, there are two half shafts, one going from the driver side rear wheel to the differential housing and one going from the passenger side to the differential housing.

Should you be driving down the road and hit a bump or a section of uneven pavement, your S550 Mustang will feel more planted than previous generation Mustangs as each side of the car is affected and responds independently of the other side.

Although the system isn’t worlds different (technically speaking) than the incredibly common LRA setup, it does offer a whole new level of performance/handling.

Live rear axle suspension systems are: 

• More desirable for drag racing
• Better at straight-line acceleration
• Tend to be able to handle higher horsepower on stock components
• Cheaper to service and replace

Independent rear suspension setups are:

• More desirable for track racing/handling
• Less “squirley” and unpredictable
• Provide a smoother ride
• Can provide greater grip than LRA suspension systems

While the axle setup is one of the most obvious differences with IRS Mustangs, there are a handful of other parts that don’t transition over from LRA equipped Mustangs. While some of them serve the same purpose, the enhanced grip and articulation of IRS systems requires a few additional parts to control the car.

• Vertical Links – these basically replace the lower control arms on LRA setups and work to keep the wheels planted, especially under load. 
• IRS Bushings – unique to IRS setups, IRS bushings work to defeat deflection under load and wheel hop, reducing the amount of give/flex of the axles
• Rear Toe Links – serving a similar purpose and function as upper control arms, rear toe links allow the wheels on IRS S550 Mustangs to stay planted and adjust to lowered ride heights. These are crucial for maintaining a consistent and well-planted contact patch for the tires. 
• Craddle-Bushing Lock Outs – These help keep the IRS cradle planted and on the ground, cutting down on deflection and wheel hop.

Live rear axle Mustangs can improve drastically with extensive aftermarket modification, but they will never quite perform like an IRS equipped S550, especially with the same amount of money put into it. The biggest issue with live axles is when you're going over anything other than a flat surface, the tires will be tilted, decreasing traction. The Some S197 owners turn to mods like Watts-Link Suspension setups to help with the articulation and responsiveness of the setup, which ultimately tries to replicate the handling profile of an IRS setup. If you're looking at adding a Watts-Link or panhard to an older Mustang like a Foxbody or an SN95, you might run into clearance issues with the gas tank and/or exhaust system. The aftermarket does offer specially designed units, but be sure to check the manufacturer specs before committing to the expense. 

Make no mistake, with the right modifications you can greatly improve an LRA’s handling abilities, but it will never be an optimal replacement or successor to IRS setups, especially in terms of overall smoothness while driving and track racing.

There seems to be this misconception in the Mustang and racing community that IRS equipped 2015+ Mustangs can’t quite hang with its predecessors in the quarter mile. An IRS powered S550 Mustang can be as competent as the Mustangs of yesteryear and can easily dip into single digit time slips.

Just like LRA Mustangs, and IRS S550 will need a little loving to perform at the top of its class, which mainly comes from replacing the half shafts. The half shafts are the biggest weak point in the whole system and can fail, especially when launched at the track on a sticky tire. Luckily for enthusiasts, aftermarket half shafts are readily available and easy enough to replace.

Half shafts are rated by the amount of horsepower they can safely withstand, allowing you to pick a set ideal for your build. If you are shooting for an S550 that puts down 600 HP and runs 10s, you don’t need the biggest, baddest half shafts available. You can buy ones rated for 800 HP rather than the 1k shafts.

The 2015 Mustang is not the first Mustang to use an independent rear suspension setup, contrary to what some may believe. The 2003 and 2004 Cobra Mustangs, aka Terminators, were the first to use an IRS setup. However, due to some minor backlash in the community and issues with the IRS system, Ford never made it mainstream—at least not until 2015.

The ’03 – ’04 Cobra IRS system is quite a bit different from the much more modern/advanced S550 Mustang. Poor half shaft design resulted in quite a few hardcore drag racers replacing the IRS system with an LRA setup. While a step in what many would consider a step in the right direction, the 2003-2004 Cobra IRS system needed some major tweaking and revisions. One could argue those cars are the reason we have IRS in the mainstream Mustang today.

There are a few common problems that impact all stock Mustang owners and their handling. Wheel hop. This is when your rear axle bounces up and down as it struggles to get traction, and is a common issue on all Mustangs, especially the S550 models. Mustangs can also suffer from body roll off the line and going around turns due to lack of stiffening and support throughout the frame. Any gen Mustang can feel somewhat floaty and high up due to the stock spring ratios, which are great for daily driving and absorbing bumps and potholes, but awful for handling and curbside appeal.

Non-IRS equipped Mustangs (basically everything prior to 2015) can have issues in turns due to the solid rear axle (SRA) design that gets ‘twitchy’ when it hits a bump or uneven pavement. S550 Mustangs specifically can have trouble getting off the line and launching due to weak IRS bushings having trouble keep the rear axles planted.

From the factory, Ford uses rubber bushings throughout the Mustang's suspension. While rubber bushings aren't the best option from a performance standpoint, they do help keep the cost down and provide a smoother ride by controlling what's called NVH (Noise, Vibration, and Harshness). Keep in mind many Mustang owners never modify their car, so Ford's use of rubber bushings makes sense in that regard. Since rubber bushings suffer on the performance side, they're a contributor to wheel hop.

If eliminating wheel hop is a priority, then replacement bushings should be a priority. While there are a few different types of materials available, the most commonly used is polyurethane. Polyurethane bushings will provide a much firmer feel than factory rubber pieces and, when properly maintained, will outlast the stock components. While not the stiffest bushings, they're an ample upgrade from the factory rubber. They give slightly more NVH than rubber bushings, and they do need to be greased every few months, however. These are fantastic for a daily driver.

Spherical Bushings: a better type of bushing than poly, they are fantastic for drag launches and perform quite well in all applications. Their main drawback is simply the amount of increased NVH, primarily the noise. For a daily driver they are not optimal. The noise tends to get quite irritating. That being said, many use them without complaints.

Aluminum: similar to poly bushings, they’re great all-rounders. They're stiffer and have a little more NVH than poly bushings. While it takes a little bit of time, they are susceptible to corroding as well. If you're a road racer though, they can withstand much higher temperatures than rival bushings, fantastic for when the rear end generates a lot of heat.

S550 IRS bushings are crucial for owners aiming to drag race their pony as they take a lot of slack/slop and play out of the suspension. The stock bushings allow rear subframe movement that can ruin a quarter mile time. Aftermarket IRS bushings help the S550’s rear feel more solid and planted, especially when taking off from the line.

An upgrade made popular by S197 Mustangs and has since spread out to other gens is replacing the main bits of the suspension with an air lift suspension kit. Air suspension kits remove the shocks, struts, and springs, replacing them with a pneumatically controlled airbag and air spring. These kits allow for extreme lowering (up to 5 inches) and can raise the suspension up to 1 inch over stock. Air lift kits are typically used on show cars, however they do maintain solid performance in the turns and off the line.

A bonus of air ride is you can adjust for awkward driveways and parking lots. A static lowered Mustang may be an unrealistic upgrade depending on the roads you travel. When thinking about air ride vs. lowering springs, you should think about places you visit on a regular basis such as stores and your job. Other things to consider are routine maintenance. Can you get a jack under the car to lift it when changing your oil, or will you also need to get some ramps to raise the car enough to use the jack? After considering all the potential issues, you may want to lower a car a little less you had originally intended, or that an air ride setup is more appropriate for your build.

Mustang coil over kits replace the stock shocks, struts, and springs with one all-encompassing unit that provides a static drop height. Some of these kits allow you to preset/predetermine how low you’d like to go, but the average drop you can expect from a coil over kit is anywhere from 1 inch to 2.5 inches.

Coil over kits are not necessarily ideal for daily drivers as they will absorb bumps and potholes less efficiently, but they will provide arguably the best handling setup when compared to your other options.

Most suspensions parts can be self-installed within a few hours. The primary reason for not self-installing certain parts are ones that require an alignment afterward (CC plates, toe links, etc.), or parts that require welding (torque box modifications, subframe connectors). However, for items like control arms (front and rear), sway bars, springs, shocks, struts, panhard bars, etc., can all be installed provided you have the proper tools. Although ball joint replacement/modifications require specifically designed removal tools. The key is to make all suspension modifications with no load on the parts. Once installed, hand tighten the bolts and then lower the vehicle down before torqueing them to spec.