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The Ultimate Mustang Suspension Guide - Everything You Need to Know

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Contents
  1. What is Camber?
  2. What is Caster?
  3. What is Toe-In and Toe-Out?
  4. What is an Alignment?
  5. The Mustang Uni-Body Chassis
  6. Mustang Suspension Parts 
  7. Common Mustang Front Suspension Components
  8. Common Mustang Rear Suspension Components
  9. What's the Difference Between 4-Link and 3-Link Suspensions?
  10. Common Mustang Suspension Issues
  11. What Do Mustang Ball Joints Do?
  12. What is Bumpsteer & What Do Bump Steer Kits Do?
  13. Control Arms – For Lowered Mustangs
  14. VIDEO: 2005-2010 Ford Racing Front Control Arm Review & Install
  15. Adjustable Control Arms vs Non-Adjustable Control Arms
  16. What Do Mustang Sway Bars Do?
  17. Shocks and Struts – Control and Adjustment
  18. Springs – Lowering and Stance
  19. VIDEO: 2015-2017 Mustang Sport Spring Review & Install
  20. A Note About Mustang Rear Springs and Rake
  21. Various Spring Rates for Lowering
  22. Standard Rate Springs vs Progressive Rate Springs
  23. Can I Modify My Stock Springs?
  24. What Do Mustang Strut and Shock Tower Braces Do?
  25. Mustang Rear Shock Braces
  26. What Do Mustang Panhard Bars Do? 
  27. What Do Mustang Suspension Bushings Do?
  28. VIDEO: 1979-2004 Mustang Polyurethane Spring Busings Review & Install
  29. What Do S550 Mustang Vertical Links Do?
  30. What Do S550 Mustang Toe Rods Do?
  31. Mustang Air Lift Suspension Kits
  32. Mustang Coil Over Kits
  33. Adjusting Alignment with Caster/Camber Plates
  34. Mustang Subframe Connectors and Bracing
  35. Bolt-On Subframe Connectors
  36. Welded Subframe Connectors
  37. Special Information Package Regarding Convertibles
  38. Mustang Torque Box Braces
  39. Mustang Roll Bar/Roll Cage
  40. Which of These Parts Can I Install Myself?
Shop Mustang Suspension

Whether you're looking for better cornering or more bite off the line, there's plenty that can be done to improve your Mustang's stock suspension. Start modding now and feel the differences that even a simple chassis brace can have no your entire driving experience.

Mustang Suspension >>

The stock suspension setup on the Mustang is great for daily drivers with no modifications, but it can leave a lot to be desired for your average gearhead. The S550 Mustang made drastic improvements to the suspension setup from the factory, but still struggled in some areas. Regardless if you are a drag racer or corner carver, upgrading your suspension will make you faster in a straight-line and in a turn. This guide will give you an overview of all of the different parts and terminology regarding your suspension system and what you need to know before modifying them.

What is Camber?

Camber is how the tire leans 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 not always going to be the case.

A little negative camber can enhance a vehicle's cornering ability, allowing the outside tire to grip better in the corner since the lower side of the tire will have a tendency 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 car, you also change the camber angle of the front wheels. If this is left out of spec, it can dramatically affect tire wear. In some cases, all that’s needed is a trip to the alignment shop. The more lowering involved, however, the more you may find yourself needing to enlist the help of camber plates for your front shock towers.

What is Caster?

Caster describes the relationship between the steering axis and a true vertical position. In the case of 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.

What is Toe-In and Toe-Out?

Toe angle refers to the relationship of the tires to one another, in regards to the direction they are pointed. Toe-in has the two tires pointing slightly together, while toe-out has them pointing slightly apart. A slight amount of toe-in helps higher speed stability, as the wheels will toe-out slightly as speeds increase.

What is an Alignment?

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" can refer to factory specs, or, in the event of a race-prepped car, some more aggressive settings intended to help 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 has the capability to accurately measure your front suspension adjustments. 

Major Mustang Suspension Components: A vehicle's suspension involves several components, each serving an important task. As a whole, they all work together, giving the vehicle its handling characteristics. Knowing what these components are is the primary step to understanding how the suspension works.

Mustang Foxbody with a Multitude of Suspension Components

The Mustang Uni-Body Chassis

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 the chassis of the car is stressed. 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 also help reduce body flex in a different way than subframe connectors
  • Some strut braces have the clearance for supercharged engines
  • 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. Depending on your end goals, this might also be the best option
2010-2014 Mustang Boss 302 Drifting

Mustang Suspension Parts 

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

Common Mustang Front Suspension Components

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. Up 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 and is used to help control body roll.

1983-1993 5.0L Mustang Foxbody with Front Sway Bar
Foxbody with a Front Sway Bar

Common Mustang Rear Suspension Components

Up until 2004, the late model Mustang used a four-link rear suspension. Two upper and two lower control arms hold the rear axle in place, giving the suspension its four-link moniker. Springs are used to support the rear of the car, above the axle, with separate shocks installed to control the dampening.

Depending upon whether the 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. The change to this arrangement was a tradeoff between a full independent rear suspension and a solid axle. 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 axle anyway, as it's more suitable for dragstrip duties. The panhard bar setup still allows the Mustang to keep the solid axle while providing cornering ability improvements that suit most owners better than previous generations of the Mustang.

What's the Difference Between 4-Link and 3-Link Suspensions?

A 4-link suspension is a suspension that consists of four total parts. There are (2) upper control arms and (2) lower control arms. This method of rear suspension was used from 1979-2004 model Mustangs (regardless of model).

A 3-link suspension is similar to a 4-link suspension. While there are (2) lower control arms, there is only (1) upper control arm. This is remedied by the addition of a panhard bar. There is a bar that connects one end of the axle to the vehicle itself (like an upper control arm does).

2005-2014 Mustang GT Coupe with Aftermarket Shocks, Springs, and Sway Bar Installed
GT Rear with Aftermarket Shocks, Springs, and Sway Bar Installed

What is an Independent Rear Suspension & How Does it Work? 

IRS setups allow both wheels to function and move independently of the other. This allows for greater control and handling of your vehicle. 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.

Differences & Benefits of IRS and LRA Mustang Setups

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

What Parts are Different on IRS Mustangs?

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.

IRS Handling Pack Components

Can an LRA Mustang be Modified to Perform Like an IRS Equipped Mustang?

Live rear axle Mustangs can improve their handling drastically with extensive aftermarket modification, but they will never quite perform to the same level as an IRS equipped S550, especially with the same amount of money put into it. Some S197 owners turned 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.

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


S197 LRA Watts Link Setup

Are S550 Mustang’s Good For Drag Racing? Will The IRS System Break? 

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. This is false and needs to be dispelled. An IRS powered S550 Mustang can be just as competent as the Mustang’s 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 in the form of replacing the half shafts. The half shafts seem to be 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 are easy enough to replace. 

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

Is The 2015+ Ford Mustang Really the First Mustang to Use an IRS Setup?

The 2015 Mustang is not the first Mustang to use an IRS setup, contrary to what some may believe. The 2003 and 2004 Cobra Mustangs, aka Terminators, were actually 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 that those cars are partially the reason we have IRS in your mainstream Mustang today. 

Common Mustang Suspension Issues

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 that have trouble keep the rear axles planted.

1999-2004 Cobra Mustang Front IRS Differential Mount Bushings

What Do Mustang Ball Joints Do?

Ball joints eliminate the sloppy steering feel Mustangs can sometimes suffer from. When ball joints get worn out, they clunk and squeak when going through a turn while feeling incredibly loose. A great time to upgrade them is when the stock ones wear out, giving you not only revitalized steering and handling, but overall improved performance. 

What is Bumpsteer & What Do Bump Steer Kits Do?

Bumpsteer is a change in toe angle caused by the suspension moving up or down. Bumpsteer is built into the geometry of the Mustang’s suspension and steering system and has nothing to do with turning the steering wheel. The effect of bumpsteer is when the wheel toes-in or toes-out when the suspension moves up or down. This toe change or "steering" occurs any time the suspension moves due to the tie rods traveling at a different rate than the control arms. Whether it is from body roll, brake-dive, or hitting a bump in the road, bumpsteer is undesirable because the suspension is steering the car instead of the driver.

When bumpsteer occurs, the front of the tires will change slightly in their relation to one another. This is due to the tie rods traveling at a different rate than the control arms. There will always be some bumpsteer in a Mustang's suspension, but this can be exaggerated if the car is lowered. The use of a bumpsteer kit will help eliminate this, by repositioning the tie rod ends and realigning/correcting the geometry of your Mustang's front end suspension.

2015-2017 Mustang with a Bump Steer Kit Installed
Bump Steer Kit Installed

Control Arms – For Lowered Mustangs

Control arms are one of the biggest and most popular Mustang suspension modifications as they help to keep the wheels planted. There are rear and front control arms, along with upper and lower control arms. Rear lower control arms are the major key to hooking up and getting off the line as they keep your tires firmly planted.

In addition to quicker launches, control arms also offer better stopping performance by keeping your tires on the road rather than hopping to a stop. Stock control arms were not designed to withstand hard launches and performance use, let alone the huge power upgrades that many Mustang enthusiasts perform. They are often constructed of U-shaped bent steel that can flex under pressure such as accelerating from a stop. Upgraded control arms often come in cylindrical or box shaped, reinforced steel with polyurethane bushings maximizing smoothness while not sacrificing strength. Some control arms even offer a greasing point to ensure constant lubrication.

VIDEO: 2005-2010 Ford Racing Front Control Arm Review & Install

Adjustable Control Arms vs Non-Adjustable Control Arms

The big question you’ll have to ask yourself when buying control arms is if you want adjustable or non-adjustable control arms. Adjustable control arms allow you to dial in and fine-tune the suspension to your exact liking. Non-adjustable control arms are like a one size fits all. Instead of using rear control arms, S550 Mustangs use vertical links to keep the rear wheels on the pavement and hooking up.

The front control arms are generally something that gets replaced on a vehicle that will see more serious track duty. Replacement front control arms can offer adjustability of your roll center and bumpsteer. In the case of most Mustang owners, replacement of the rear control arms is a very useful upgrade. Replacement upper and lower rear control arms allow you to bring the vehicle back into spec after lowering it. 

2005 Mustang Note: When lowering your Mustang, the three-link suspension can negatively affect the pinion angle. An incorrect pinion angle can cause undesired stress on the universal joints, excessive drivetrain noise or vibration, or even possible contact between the underside of the car and the rear axle. Upper control arms combat this.

1979-2004 Mustang Adjustable Rear Upper Control Arms
Adjustable Rear Upper Control Arms

What Do Mustang Sway Bars Do?

Mustang sway bars eliminate body roll and keep your Mustang feeling stiff in the corners. As the body leans, grip is transferred from one side of the car to the other. While some weight transfer can be beneficial, too much can adversely affect handling.

Keeping the car flatter in turns provides more even grip at the tires on both sides of the car, which helps to neutralize excessive oversteer. A car that leans too much will apply more traction to the wheels receiving more of the weight. This can unload the differential, and causes oversteer. 

Your Mustang has two sway bars, one in the front and one in the back. The factory sway bars are non-adjustable. However, you can buy adjustable and non-adjustable aftermarket upgrade options. Sway bars are an excellent complement to a set of control arms in terms of overall handling prowess. Drag racers often remove their front sway bar to get improved weight transfer while dropping a few pounds off of the nose as well. 

The front sway bar connects to end links which then connect to the control arms and the chassis itself by mounting with rubber or urethane bushings. The rear sway bar connects to each of the lower control arms. On a Mustang, the rear sway bar should always be a smaller diameter since the car is rear-wheel drive. A bigger sway bar in the front increases lateral and motive traction in the rear and in cases where the rear sway bar is the bigger of the two this causes an increase in traction of the front tires.

2015-2017 Mustang with Rear Sway Bar
Rear Sway Bar on a 2015-2017

How Do End Links Work?

In addition to upgrading the anti-roll bars, the aftermarket offers various types of end-links which attach to the anti-roll bar and the lower control arm. Adjustable end-links offer further control over the tuning of the suspension and are an important addition to lowered vehicles as they help correct the altered geometry of the suspension.

Adjusting the preload of the bar will tailor the handling for whatever street/track setup you are looking for. They’re also usually stronger and lighter than the factory pieces, and some offer greasable fittings which (with regular maintenance) reduce noise, vibration, and harshness (NVH).

Shocks and Struts – Control and Adjustment

A critical component of any vehicle are the shock absorbers or dampers. These are arguably the most influential element of ride quality and handling. Their job is to control the movement of the vehicle as it travels over surfaces and around corners as well as under braking and acceleration. Aftermarket offerings for the Mustang include non-adjustable, single-adjustable, and double-adjustable. Shocks and struts also hold your Mustang up and help it to turn in. The shocks are in the rear and the struts are in the front of your Mustang, and they are encased by your Mustang’s springs. When you lower your Mustang with a set of springs, you will want to consider upgrading the shocks and struts as well to maintain a balance throughout the vehicle. Going to a set of aftermarket shocks and struts will make you feel those little bumps in the road a bit more, but they will also drastically improve your handling and weight transfer throughout the vehicle.

Single-adjustable shocks will allow you to adjust the valving to suit your driving style and road/track conditions. Some units control only rebound while others control compression and rebound with one single dial. A double-adjustable shock/strut is the ultimate in adjustability allowing for fine-tuning of the compression and rebound curves separately to suit any combination of suspension upgrades. Upgrading your Mustang’s shocks/struts will:

  • Improve tire to road contact
  • Improve control in cornering, acceleration, braking, and quick steering input
  • Adjustable shocks allow a tailored driving experience

When adding a lowering spring, it is often recommended you pair it with a performance shock/strut designed to work with the shorter travel and firmer rate of the spring. Look for companies who offer complementary kits which include both springs and shocks for a very effective suspension upgrade. As spring rates and ride heights change, so does the dampening needed from the shocks and struts. The springs' job is to support the vehicle while the shocks and struts control the rebound of the spring, preventing the ride from being too bouncy and handling poorly. So the strength of the spring will dictate the action required from the shocks and struts. You can also change the shocks and struts while keeping the same springs, to control how the suspension reacts and handles, should you desire to have either a slightly looser or firmer feel. 

Aftermarket struts (and shocks) are always recommended when lowering a Mustang. As we've mentioned, the stock struts were designed for the stock spring specs. As a result, they are not intended to be used under lowered conditions. While they most certainly can work under lowered conditions, it is not optimal. This will lead to quicker failure and replacement of the struts. This also applies to rear shocks.

2005-2010 Mustang with Eibach Struts

Springs – Lowering and Stance

Replacement springs serve two main purposes: to alter the vehicle's handling and to lower its stance. When replacing your springs, it's wise to closely examine your needs. Are you looking to improve handling, and if so, by how much? If you want to lower your Mustang, how far do you want to go? The spring options and characteristics are nearly infinite, so properly planning a spring swap is important.

Measuring from the ground to the fender, below is a list of stock Mustang ride heights (Note: depending on how worn your springs are, your ride height can change):

  • 1979-1993: 26" front, 26.75" rear
  • 1994-2004: 27.5" front, 28.25" rear
  • 2005-2014: 28.6" front, 29.3" rear
  • 2015-2018: 28.5" front, 28.75" rear

Mustang springs go around the shocks and struts and help to control your vehicle, specifically when launching off the line or in a turn. Springs have progressive rates that take an increasing amount of force to compress the spring the same amount of height and there are linear spring rates that require just as much force to compress it the first inch as it would the third inch.

Progressive spring rates are considered to be better for daily driving and cornering, while linear spring rates are better for drag racing.

VIDEO: 2015-2017 Mustang Sport Spring Review & Install

Springs are the easiest way to lower your Mustang, providing anywhere from a half an inch to two inches of static lowering. When you lower your Mustang with springs, you will want to also upgrade the bump steer kit, the shocks and struts, and caster camber plates. Springs are also a nice appearance modification as they help to eliminate that horrible factory wheel gap, dropping your Mustang, and lowering the center of gravity for increased nimbleness in the turns. Mustang lowering springs can drop your ride anywhere from 0.5” to 2”, but it depends upon the manufacturer and product line. Lowering springs offer a static drop that lowers your Mustang to a fixed height. Going any lower than 2” would make daily driving almost impossible and at the very least unbearable

One thing you want to want to pay close attention to is the fitment for the springs you’re considering. Lowering springs are designed to handle and distribute the precise weight of your Mustang evenly and accurately. You want to make sure to purchase a set of springs intended to support and lower your car to the listed specs. Some springs are made to support both coupe and convertible while some others are not; similarly, some springs are designed for both V6 and V8 models, while others aren’t. We encourage you to stick with a spring created with your year and model in mind to get optimum results in both handling and appearance. Springs will be tuned for a certain weight and will be intended for a certain type(s) of car.

Also keep in mind that lowering your Mustang doesn't come with a complete list of benefits. There are some downsides too. By lowering your ride height, you've also limited your suspension travel. Aftermarket springs will provide a stiffer ride, which is ideal for launching and cornering, but will make for a bumpy ride for daily driving.

  • Lowering requires suspension components to work harder and ball joints, wheel hubs, tie rods, shocks, and struts are all under more strain
  • The ride will be much firmer and may not be as comfortable when hitting bumps in the road
  • A mild drop (1" - 1.5") would help any vehicle with increased handling performance while not substantially affecting ride quality or reducing life on the suspension
  • Dropping the vehicle (1.5" or more) will produce a harsher ride and more frequent suspension component repairs. The vehicle will also require more heavy duty aftermarket components to keep the car's suspension true and straight. These include panhard bars (2005) and caster camber plates
  • As you lower the vehicle further, you will also need to monitor your wheel fitment to ensure your wheels are not rubbing during turns or during periods of high travel

A Note About Mustang Rear Springs and Rake

The Mustang has a natural tendency to sit a little higher in the rear than in the front. So some owners may find themselves simply wanting to level the car instead of lowering it. To achieve this, you’ll find a few kits on the market specifically for this task. Roush is one of the more commonly used sources for this sort of spring kit. 

1979-2004 Mustang with Drag Launch Springs
Drag Spring Setup

Various Spring Rates for Lowering

The lower the car, the more important the rate becomes. This is because you have less suspension travel to absorb impacts. With the appropriate springs, however, you can lessen the stiff ride and save yourself multiple dentist trips. Your goals should also take into account what spring rate is ideal for your situation.

Ultra-Lite: The reasons you wish to change your springs also weigh into the equation. While most people simply want to lower their car for appearance reasons, there are some who are doing it from a performance standpoint. If you fall into the former category, you may want to use a lighter spring to keep the ride quality of your Mustang as close to what it was before. Springs in this category are referred to as Ultra-Lite Springs.

Sport: If you’re looking to tighten up the feel of the suspension, you may want to investigate Sport Springs. Sport Springs are a little stiffer than stock, but offer a good compromise between stock and some added performance. They are a middle of the road option for those looking to keep the stock ride, but aren’t going to do any serious track racing. Keep in mind I’m referring to road racing, not drag racing. We’ll discuss drag racing in a moment.

GT500 Mustang Lowered

Competition: Competition spring rates throw ride quality out of the equation in favor of handling and performance. These types of springs are typically used for cars that see a large amount of track time. While they can be used on the street, ride quality will definitely be much harsher than with the stock springs. They will also be harsher than springs in other categories.

Drag-Springs: Drag racing springs are very different from the other types, but just as with the competition springs they are best suited for track use. The difference, when compared to the competition springs, is drag springs allow the suspension to have a much fuller range of movement. This is due to a softer spring rate which reduces cornering ability. The car will launch at the starting line with a little more authority, however, since the spring rate allows the weight of the car to transfer to the rear wheels better than with other springs. This helps the car hook up and get power to the ground.

2003 Cobra Mustang on a Drag Strip

Standard Rate Springs vs Progressive Rate Springs

Standard Rate Springs: are geared more toward those who don’t mind sacrificing some ride quality for ultimate performance. These springs will be firmer at all times, which doesn’t allow them to absorb as much of the road as progressive springs and offer a bit of a harsher ride even over small bumps. Standard springs have a spring rate that rises in a linear manner. While the spring rate can increase as the spring is compressed, it rises in a predictable manner. For example, at the first inch of travel, it may be a 50 lb. rate while at 2 inches it will be 100 lbs., and at 3 inches a 200 lb. rate.

While the rate will vary from spring to spring, the increase in rate is predictable. Standard springs are most often used for drag and road racing applications, as their linear rates allow the driver to more accurately predict how the suspension will react.

Progressive Rate Springs: are daily driver friendly and ultimately offer a comfortable ride similar to stock during normal driving conditions. Another benefit of progressive springs is they help to achieve higher performance when driving hard. These springs have larger gaps between coils at one end than the other. This allows the spring to compress and firm up to reduce squat during acceleration, body roll in corners and excessive nose-dive under hard braking. The rise in spring rate is not linear, allowing for a softer spring rate in the early stages of travel, but a much stiffer rate as the spring is compressed further. So while the first inch of travel may be at a 50 lb. rate, the second inch of travel may step up to a 200 lb. rate, and continue to increase from that point.

Progressive springs find more of a use on the street. Since they can have a much softer initial rate before they get stiffer makes them ideal for maintaining ride quality while still preventing the car’s suspension from traveling too far when necessary.

2015-2017 Mustang Progressive Rate Springs
Progressive Rate Springs

Can I Modify My Stock Springs?

To put it simply: NEVER modify your stock OEM springs and other suspension components by cutting it up. This will very negatively affect your performance and handling. Cutting springs to lower the vehicle will unpredictably affect the spring rate and could cause damage to your vehicle. If you are looking to lower your Mustang, do it properly with the right parts that have been tested and vetted with rigorous R&D.

What Other Suspension Upgrades Should I Add With Lowering Springs?

Depending upon what you plan on doing with your build, there are a couple of other mods you’ll want to consider when adding lowering springs to your Mustang. Some mods you’ll want to consider are:

•    Rear lower control arms
•    Rear upper control arms
•    Panhard bars
•    Shocks and Struts
•    Sway bars

Upgrading the suspension on your Mustang is a process that will require a lot of fine-tuning and tweaking to get your desired result. Adding a set of lowering springs to your Mustang is just one part of the equation and there are multiple other parts you can swap out that will all work to improve your handling.

What Do Mustang Strut and Shock Tower Braces Do?

The front strut/shock towers are another point on the Mustang chassis that can benefit from some additional strengthening. These towers serve as the mounting point for the struts, and therefore they are the recipients of a great deal of stress. In fact, with the proper tools, you can even measure small changes in the relationship of the shock towers to one another when the vehicle is jacked up as opposed to resting on the ground. Knowing that one can easily see why hard cornering could cause chassis flex in this area.

To combat this, you can install a brace that will tie the two towers to one another. This reduces flex thanks to the tubular or bar-shaped section that's used for the main body of the brace. Different connectors may use either two, or four of the bolts on each shock tower. The use of all four bolts provides more rigidity, but visiting the alignment shop afterward is a good idea, as removing all four bolts for installation can alter your vehicle's alignment.

Mustang GT with a Strut Tower Brace

A shock tower base goes from the top of the driver’s side shock to the passenger’s side with a piece of metal to brace your Mustang and provide increased frame rigidity. Strut tower braces, the more common of the two, do the same thing, but in your engine bay going from strut to strut. Adding a strut or shock tower brace to your Mustang will help it feel more planted when turning, reducing the amount of body roll and chassis flex that the platform is prone to. A shock and strut tower brace are highly recommended if you autocross or drift your Mustang because these are the situations where you will notice a difference the most due to the increased speed and subsequent flexing. 

Keep in mind front shock tower braces will need to clear your plenum or supercharger (should you have one). Not all braces are created with this boost or aftermarket plenum covers in mind. Be sure to read up on the brace you're interested in before pulling the trigger.

Mustang Rear Shock Braces

Just like the front strut tower brace, a rear shock tower brace can reduce unwanted flex as well. The rear shock towers are generally not under as much stress as the front, but if you're looking to continue strengthening your Mustangs chassis, a rear shock tower brace will certainly do it. There are fewer options for rear shock tower braces, but there are still plenty to choose from. Most rear shock tower braces will also require some welding as well, which makes installation more complicated than a simple bolt-on affair.​

Mustang GT Strut Tower Brace with a Supercharger

What Do Mustang Panhard Bars Do? 

Panhard bars are only found on Mustangs up until 2015 as they are needed on solid rear axle (SRA) cars. Panhard bars work to keep your Mustang's rear axle centered, reducing lateral movement. Panhard bars work to correct rear steer and allow your SRA equipped Mustang to handle more consistently and predictably while cornering. 

Panhard bars are a required upgrade when you lower your Mustang as you will need to adjust the rear axle. Panhard bars are available in both adjustable and non-adjustable varieties, with adjustable bars being more ideal for lowered cars and competitive builds.

Another alternative to panhard bars is a watts link setup that will replace the panhard bar, taking on all of the same responsibilities while also helping to prevent vertical movement. Watts link suspension systems help to make an SRA equipped Mustang feel more like an IRS equipped one.

2005-2014 Mustang with an Aluminum Adjustable Panhard Bar
Aluminum, Adjustable Panhard Bar

What Do Mustang Suspension Bushings Do?

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 a large number of Mustang owners never even really 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 handling and eliminating wheel hop is a priority, then replacement bushings are the answer. While there are a few different types of materials available, the most commonly used option is polyurethane. Polyurethane bushings will provide a much firmer feel than the factory rubber pieces and, when properly maintained, will outlast the stock components. While they're not the stiffest bushings manufactured, 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 the most optimal. The noise tends to get quite irritating. That being said, many do it without complaints. 

Aluminum: similar to poly bushings in that they are great all-arounders. They're stiffer than poly bushings however and have a little more NVH. 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 2015 Mustang owners who want to drag race their Mustang as they take a lot of slack/slop and play out of the suspension. The stock bushings can allow rear subframe movement that can absolutely ruin a quarter mile time. IRS bushings help the S550’s rear feel more solid and planted, especially when taking off from the line.

VIDEO: 1979-2004 Mustang Polyurethane Spring Bushings Review & Install

What Do S550 Mustang Vertical Links Do?

Vertical links are essentially rear lower control arms for IRS cars. Due to the design of the IRS system, traditional control arms don’t fit/have the same impact. Instead, vertical links are used to keep the rear wheels planted. Their primary purpose is to reduce knuckle deflection under load, limiting the fore and aft movement of the knuckle. This prevents the knuckle from binding up as the axles turn, allowing you to put your power to the pavement more efficiently. You may also see these referred to as integral links. They function almost identically to lower control arms and are responsible for reducing wheel hop in an S550 Mustang. From the factory, the Mustang is equipped with stamped steel pieces which are weak and can deflect under load. Some aftermarket solutions are fully adjustable allowing more tweaking to your vehicle's handling. By switching to an adjustable link, you are able to precisely dial in your camber. This is another critical step when lowering your Mustang, as extreme camber can cause uneven tire wear or poor handling characteristics.

Non-adjustable camber links can still offer rigidity and reduced deflection over the OEM links. If your camber is in spec without needing adjustable links, a set of non-adjustable links can reduce suspension deflection and prevent camber excessive camber changes during suspension travel.

2015-2017 Mustang with Billet Aluminum Vertical Links (Spherical Bushings)
Billet Aluminum Vertical Link

When Should I Upgrade My Vertical Links?

Anyone who is planning on doing performance driving with their Mustang should replace their vertical links with an upgraded set. Having a more robust set of vertical links will help to reduce knuckle oscillation, deflection, and provide you with more consistent rear suspension characteristics. With the reduction in deflection also comes more consistent geometry changes, a more predictable rear suspension, and a reduction in wheel hop. Wheel hop is the enemy of traction and performance, so anything you can do to reduce it will help your Mustang have more consistent traction. Eliminating wheel hop will also prevent axle shafts from snapping and causing damage to your Mustang.

Types of Vertical Links

Vertical links come in three different types, bearing/bearing, Delrin/bearing, and Delrin/Delrin. Bearing/bearing vertical links have spherical bearings on both ends and allow articulation while eliminating deflection. These are a popular choice for street cars because they still allow for movement over uneven surfaces. Delrin/bearing arms are also a popular choice for the street since they reduce knuckle wrap further, but still allow some articulation. The Delrin may be more prone to squeaking than a bearing/bearing link. Delrin/Delrin vertical links should be reserved for race applications only. They completely eliminate knuckle wrap, but increase the chance of damaging your suspension on the street. The solid nature of Delrin also will lead to more noise, vibration, and harshness (NVH) over a bearing/bearing arm.

What do S550 Mustang Toe Links Do?

Toe links work like a bump steer kit and help to keep the toe angle of your rear wheels within spec. Toe links optimize and improve traction, especially off of the line, and provide a more balanced ride. When toe settings are set incorrectly, your tire will drag or skip along the road surface instead of smoothly rolling. From the factory, Mustangs have stamped steel rear toe rods with rubber bushings. These factory rods will deflect under heavy loading, allowing the rear wheels to toe in or toe out. This can lead to erratic handling characteristics or uneven tire wear. Installing adjustable toe rods are an excellent idea when lowering the vehicle. It allows you to correct rear end geometry after lowering and keeps the toe settings locked in place by reducing deflection. Non-adjustable toe rods can be used as well, but should be reserved for Mustang owners who don’t plan on lowering their cars. Without the adjustability from the toe rod, your alignment specs may be stuck in an unfavorable position.

An upgrade to an adjustable rear toe link offers many improvements:

  • Stiffer steel tubing with Heim joint construction
  • Fully adjustable to dial in handling
  • Reduced deflection helps to eliminate wheel-hop
  • Bolt lockout plates to prevent bolt slip and changing alignment specs after they have been set

Elimination of flex in the chassis is a goal of any owner who wants to get the best handling from their Mustang. Any flex will affect alignment angles leading to decreased control and steering feel. When shopping for a toe rod, be sure to choose one with a threaded adjuster. Threaded adjusters are more accurate, easier to use, have greater adjustment range, and are not prone to slip like toe rods that utilize eccentric bolts. You should also consider choosing a toe rod that has a bearing on it instead of a polyurethane bushing. This will allow the toe rod to properly articulate and will reduce toe deflection during suspension travel. Keeping your toe consistent will go a long way to maintaining proper steering properties of your Mustang.

Finally, a quality set of toe rods should include, a set of lockout plates for the bolts. These plates prevent bolt slip after installation, which would ruin your alignment settings. They eliminate the factory adjustment bolts; all adjustments are then made on the toe rod. Lockout plates are used to minimize to change and deflection from the factory bolt slipping and losing adjustment. We recommend lockout plates if you have more than stock horsepower, or if you're running soft compound tires.

2015-2017 Mustang Adjustable Toe Links Installed
Adjustable Toe Link Installed

Can I Keep My Stock Toe Rods?

Factory toe rods were designed with the intention of maintaining alignment with factory suspension components. When you modify your Mustang's suspension with products like lowering springs, you may end up needing adjustment outside of the range of the factory toe rods. Stock toe rods have a very small range of adjustment and can be prone to slipping if not installed and set correctly. By upgrading to a set of adjustable toe rods, you give the person performing your alignment greater control over the end result, and making it easier for them to hit their target alignment specs accurately.

Mustang Air Lift Suspension Kits

An upgrade that was 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 suspension 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 find that you want to lower a car a little less you had originally intended, or that an air ride setup is more appropriate.

2005-2014 Mustang Air Lift Suspension Kit
Complete Air Lift Suspension Kit

Mustang Coil Over Kits

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.

Adjusting Alignment with Caster/Camber Plates

Although the top of your front shock towers allow you to adjust the vehicle's camber, if you're looking to enhance handling you'll likely find the adjustability allowed is minimal. This is especially true with lowered cars, in which case, there may simply not be enough adjustability offered at all. I've seen many factory stock Mustangs prior to 2005 that have alignment issues at the factory height as the lack of adjustability can be that limited.

This is where caster/camber plates come in. Picking up where the factory adjustments options fall short, they give you a much greater range of adjustability for camber, while also adding the option to adjust your caster angle. So whether you're looking to enhance your vehicle's cornering ability, or bring it back into spec, a set of caster/camber plates is definitely a worthwhile investment.

Caster camber plates help to adjust the caster and camber of your front wheels, improving the turning radius and balance of the front end. Caster camber plates are a relatively inexpensive upgrade that provides a lot of bang for their buck and are installed atop of your Mustang’s struts for quick and easy adjustability.

2015-2017 Mustang with Caster Camber Plates
One Caster Camber Plate

Mustang Subframe Connectors and Bracing

Mustang subframe connectors help to make your ride more rigid and stiff, cutting out and down on body roll in corners and off the line. Subframe connectors can come in a variety of style from 3-point bars to x-braces in the rear seat. Additional chassis bracing helps to control and even out the weight transfer of your Mustang in turns. 

Bolt-On Subframe Connectors

Bolt-on subframe connectors are the easiest to install. They simply bolt into place between the frame rails, although some connectors may require additional holes to be drilled. Once installed, the connectors connect the front and rear subframes into a single cohesive unit. For additional strength, you can additionally weld the bolt-on subframe connectors as well, strengthening them even further. Over time, the bolts can loosen or even shift their hold, as the car's subframes try to twist apart from one another. Welding helps to prevent this.

2005-2014 Mustang Bolt-In Subframe Connectors
Bolt-In Subframe Connectors

Welded Subframe Connectors

The best options, when it comes to subframe connectors, are ones that weld into place. These subframe connectors offer improved strength because they do not rely on bolts to secure them to the front and rear subframes. Since the average person doesn't have the capability of welding them in their garage, installation will likely involve a trip to a shop that will weld them into place for you.

Special Information Package Regarding Convertibles

Due to the lack of a true roof in a convertible, the uni-body chassis is weaker than it would be with a coupe. So for most year models of the Mustang, Ford equipped them with subframe connectors from the factory. These subframe connectors are bolted into place and helped make up for the lack of the roof's ability to help strengthen the chassis frame.

Mustang Torque Box Braces

Connecting the subframes of the Mustang with subframe connectors aren't going to address all the weak spots in the chassis. While it will help, there's still another crucial area to address for drag racers launching at higher RPMs. That area is the rear torque boxes. This area catches the brunt of a hard launch, receiving a lot of stress from the axle, especially if the rest of the chassis is stiffened up already.

There are several options to choose from in regards to torque box braces. Some are smaller braces that weld in place, while others are larger and can tie the torque box area into the frame rail. You can choose between bolt-on options and those that are intended to be welded. As with the subframe connectors, welding the braces will yield advantages when it comes to strength.

1979-2004 Mustang with Welded-In Full Length Subframe Connectors
Full Length, Weld-In Subframe Connectors

Mustang Roll Bar/Roll Cage

If you want to look into the ultimate way to stiffen up your Mustang, as well as provide a safer place for the driver, look towards a roll bar or roll cage. You can get a simple 4-point bar for the rear of the Mustang, or elect to get a full cage to offer substantial protection and chassis stiffening. As with many other suspension components, you can get roll cages that bolt in place, or that require welding. Depending upon how fast your car is, some tracks may require a certain type of roll bar or roll cage. If you have dragstrip goals in mind, plan ahead. It's easier to do it right the first time than to do it multiple times. Note that for convertibles, a light bar does not fall into this category. It is merely a cosmetic feature.

8-Point Roll Cage Installed in a 1994-2004 Mustang Coupe
8-Point Roll Cage

Which of These Parts Can I Install Myself?

The majority of these pieces 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. Most of the parts can require basic hand 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 load the vehicle down, then you can torque them to spec.

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