Muscle Mustangs & Fast FordsHow To Chassis Suspension
Ford Mustang Suspension Guide - Suspension Dimensions - Tech
MM&FF Takes The Mystery Out Of Your Mustang's Suspension.
When you get in your car and head down the road or the nearest slice of racing asphalt, you often take for granted the engineering, research, and development that goes into the components that keep your ride planted to the pavement. When dealing with your Mustang or some other fast Ford, you can be sure the Blue Oval has gone through great expense to give you the best suspension for each application and price point.
Because Ford (along with every other manufacturer) must design its suspension systems for all-around use (comfort, performance, and longevity), compromises are usually made, and for us enthusiasts, those are most notable in the lack of cornering prowess. Luckily, the aftermarket is rich with high-performance suspension components that swing the balance of focus to optimal handling, whether they're upgraded, stock-style replacements or completely reengineered components.
Ask a variety of people what "handling" means and you'll get as many different answers. Nonenthusiasts may consider great handling to be a comfortable ride that absorbs the bumps and imperfections in the road and minimizes NVH (noise, vibration and harshness). Most performance enthusiasts, however, think handling means having great road-holding or grip capabili-ties. But before you can improve handling, you should know what affects it and what to expect from the changes you make to the car's suspen-sion and chassis.
Like the term "handling," the words "chassis" and "suspension" are often interchanged, but they are, in fact, totally different parts of the car. Simply put, the chassis is the frame or major structure to which all of the suspension parts are bolted, bonded, or otherwise secured. For instance, some cars and trucks have an actual frame to which the body is bolted. Meanwhile, vehicles like the Mustang have a unibody chassis structure, where the body and frame are a single structure, and the suspension is fixed to it. For the scope of this article, we'll be talking about your Mustang's chassis and suspension system and what aftermarket components are available to improve its lateral grip, ride quality, and safety.
All '79-'04 Mustangs feature a modified MacPherson strut front suspension incorporating struts, lower A-arms, and coil springs mounted between the A-arms and the K-member, which is bolted to the unibody. The system is enhanced by an antiroll bar. The front lower A-arms use rubber bushings to reduce NVH, but they can also deflect during aggressive cornering maneuvers.
Griggs Racing notes that this, as well as other compromises found in the front suspension, are made abundantly clear when driving a car with the rear suspension corrected and the front suspension is stock. According to Griggs, "Ford built the Mustang with generous steering axis (kingpin) inclination, which requires equal amounts of caster to keep the tires flat to the ground when turned. Unfortunately, Ford gave the Mustang only minimal caster-a condition we can change with caster plates and a redesigned K-member."
Also at the front, Ford's tall ride height comes into play. Lowering the entire car drops the center of gravity, but causes the front suspension geometry to lower the front roll center well below ground level. Lowering the rear roll center with a Panhard bar or Watts link in the rear suspension helps this condition, of course, but Griggs Racing says you also want to raise the front roll center, which can be accomplished by relocating the points where the front suspension attaches to the chassis. Moving the suspension pickup points is done by redesigning the K-member.
Ackermann angle is also a concern on stock Mustangs. Ackermann is the steering geometry that turns the inside front tire more than the outside tire, a necessary condition as the inside tire follows a smaller-diameter turn radius. With the Mustang, Ford ended up providing reverse Ackermann, meaning the front tires toe-in slightly when turned. This can be cured with an after-market K-member, too.
All Mustangs from 1979 and up utilize a stamped-steel K-member that supports the engine and provides mounting points for the front lower A-arms. The steel construction is cheap, quick to produce, and does the necessary job for the suspension components in addition to being part of the front crash structure. But Ford has to cut costs somewhere in order to be profitable, so you don't necessarily get the best K-member that money can buy.
One may ask why the quality of the K-member might be important, and the major concern is weight. Reducing vehicle weight has all sorts of benefits, not the least of which is better handling, braking, and acceleration. The stamped steel K-member that came on your Mustang from the factory is one heavy piece, and when combined with the stamped lower front control arms, it can be a significant chunk of ballast on your already nose-heavy ponycar. Depending on the model/ year of Mustang, there could be more than 60 pounds of weight to lose. Some aftermarket K-members also offer improved suspension geometry, but as great as these benefits sound, you'll want to do your homework before shopping for one as there are many questions you need to answer before deciding if a tubular K-member is right for you.
"K-members have become a major 'wanna-have-it' item for many people," says Maximum Motorsports' Chuck Schwynoch. "This is a serious performance modification, and people buy them without realizing all of the other requirements necessary to properly set up the car with a tubular K-member. Additional items that may be needed include front control arms, coilover conversions (that require better struts), changes to the rear suspension to properly balance the car, steering-rack bushings, adjustable tie-rod ends to adjust bumpsteer, and so on."
Schwynoch also notes that while many gearheads are capable of installing a tubular front-end assembly themselves, many fail to install it properly or get the suspension adjusted correctly. "The K-member must be properly squared in the chassis, and the bump-steer must be adjusted. It's not difficult to set up the chassis, but because it's unfamiliar to many, they avoid doing it, or it scares them away from installing a K-member completely. The skills required to install a K-member are no greater than those required to install most other aftermarket performance parts. A K-member is just as significant of a performance improvement as bolting on a supercharger."
If you decide that a tubular front end is for you, Schwynoch has some purchasing guidelines and tips that you should ask yourself and the vendor. "Research the brand," he says, "and find out who designed it and where it's made. Some are made overseas, and you can't imagine how poor the quality is. Most K-members do not improve handling and are intended to only reduce weight. Not all K-members are created equal, and very few are even as strong as a factory OEM K-member, so those other after-market units are more likely to suffer damage in minor impacts.
"With the Maximum Motorsports K-member, the tires are moved forward 31/44 inch, and some large tire-and-wheel combinations, or wheels with odd offsets, may interfere with the fenders, requiring modification. Pre-'91 Fox Mustangs are mainly affected by this, and modifications are usually fairly small, requiring one to use a spreader bar to move the lower, forward part of the fender outboard slightly."
While there are a couple of companies that offer aftermarket K-members that can be used with stock front control arms, most usually require you to use their own tubular units, many of which require a switch to a coilover-shock setup. Again, you'll want to ask questions and decide what's best for you.
With the S197 Mustang, Ford went through a lot of time and effort to pare down the chassis to a suitable weight. Some have found that there's more weight yet to be shed.
"Tubular A-arms are a lightweight alternative to your factory stamped steel arms," says BMR Fabrication's Brett Rockey. "We offer them in two styles: standard and adjustable. Both models feature CNC-machined rear pivot points, heavy-duty 1.25-inch DOM tubing, and new ball joints sourced from Ford's OE supplier." BMR's front control arms are a great example why you should do your homework before plunking down your cash, as the company claims theirs are the only ones that can be bolted to the stock K-member.
"The standard version is what we recommend for street use since it will produce the least amount of road noise, as it is assembled with high-durometer, internally fluted polyurethane bushings with grease fittings at both mounts," Rockey says.These are 11.2 pounds lighter than stock. The adjustable version is recommended for drag-race or road-race applications due to the elevated noise transmission from spherical rod ends and Delrin bushings. This version allows camber and caster adjustment not possible with OE arms, and they provide enough adjustment for up to 1.125-inch overall narrower track width (91/416 inch per side).
When the popularity of the 5.0 Mustang took off, so did the aftermarket support. The 5.0L Mustang is probably the only late-model EFI car to have its aftermarket intake-manifold choices rival those of carbureted cars from the past.The same can be said for rear-suspension components, as there are a ton of companies helping you put the power to the ground.
The '79-'04 Fox-body and SN-95-chassis Mustangs all share the same rear-suspension arrangement. Out back are four rear trailing arms (mounted between the rear housing and the unibody) along with rear coil springs (mounted between the lower arms and the unibody), and there are also two rear shocks and an antiroll bar (this differs from IRS-equipped Cobras). The rear trailing arms (also called control arms) are formed from stamped steel and can also twist, or deflect, thus leading to unpredictable handling. That said, the Mustang's rear-suspension design is probably more to blame than anything.
To get a little more insight on the Mustang's rear suspension, we called on Ford Motor Company's Jeff Feit, a suspension guru, road racer, and former Lightning engineer, who had this to say about the Pony's rear suspension setup.
"The Fox and SN-95 four-link suspension used two upper arms that were angled in rather than being parallel to themselves and the axis of the car," Feit says. "The idea was that the same arms that locate the axle fore and aft also locate it side to side. Just like most other multipurpose devices (calculator watches, Swiss army knives, combination toaster-coffee makers, and so on), they did two jobs lousy rather than one job well. Because of the extreme angles of the arms, the bushings bind in both ride and roll motion. This meant the car was prone to snap oversteer at high roll angles, so to be safe, it had to be tuned for lots of initial understeer. You ended up with a car that was an understeering pig, but if pushed hard enough, it would snap around on you. In addition, the bind meant that to keep the ride decent, the suspension had to be fairly soft to counteract the bind as the axle moved. You end up with a mushy car that still rides poorly. To top it off, the arms were so short that the suspension geometry changed drastically as they moved, and the way they were attached forced a high roll center.
"On the S197 Mustang, there are actually still four suspension links, but three of them (two lowers and one upper) are only responsible for locating the axle fore/aft. This means the upper arm can be designed for minimal bind, longer effective length, and the desired geometry. The fourth link is the Panhard rod, which is only responsible for locating the axle side to side. The link can also be designed for minimal bind, much longer effective length, and desired roll center.
"It's the same number of parts, just designed in a far better way. One of the reasons this design couldn't be used on the Fox and SN-95 is that the rear-mounted gas tank meant there wasn't enough room between the axle and the tank to fit the parts properly. While there are a number of aftermarket Panhards (and even Watt's links) for Foxes and SN-95s, it's a tight fit, and it's impossible to fit a design that meets Ford's requirements for clearance, crash safety, exhaust clearance, and so on."
As Feit stated, aftermarket companies have reengineered the Fox and SN-95 Mustang suspensions to incorporate Panhard bars, among other devices, to help correct some of the inherent imperfections. Be sure to consult with the manufacturers before you purchase one of these items, as there may be issues regarding tailpipe usage/clearance.
BMR's Rockey also explained that, "Factory Panhard rods, like on the S197 Mustang, are made with small-diameter tubing and rubber bushings that allow deflection under load." Like most other aftermarket suspension companies, BMR offers replacement Panhard rods made from large-diameter, heavy-wall tubing and utilize either greaseable polyurethane bushings or HD spherical bearings. The latter are usually adjust-able versions.
"By nature, a Panhard rod will alter rearend position as ride height changes," Rockey says. "This makes it necessary to use an adjustable Panhard rod when lowering your vehicle as it allows you to recenter the rearend. Adjustable Panhard rods also become a must-have part if you're trying to fit the widest tires possible in the wheelwell."
The Torque Arm
Another item that many aftermarket manufacturers offer is the torque arm. The stock Fox and SN-95 four-link design angles its two upper two control arms outward, which means the lower and upper rear control arms are not parallel, and as the suspension moves, the upper arms are twisted in their bushings. According to the folks at Griggs Racing, during performance driving, the stock rear set quickly leads to a near total binding of the rear suspension, called "roll bind." With the axle bound, it acts like a giant antisway bar, causing the rear roll stiffness to skyrocket and the overloaded rear tires to lose traction and spin. This is why the rearend snaps and fishtails when cornering, and why the rear tires break loose at the dragstrip once the body starts rising from the initial power hit.
Griggs Racing's answer is the use of its torque arm and either a Panhard bar or Watt's link to provide the necessary axle location. This is followed by the removal of the stock upper arms. Roll bind is then impossible, and the tires freely follow the pavement.
Use of two locating devices, such as a torque arm and either a Panhard bar or a Watts link, separates control of the fore-and-aft engine and braking loads from the lateral suspension loads, offering more precise suspension control. Griggs also noted that at this point, the rear roll center is now defined by the Panhard bar or Watt's link instead of the upper control-arm angle. In stock configuration, the stock Mustang's rear roll center is far too high, which overloads the outside rear tire and causes oversteer. By lowering the rear roll center with the Panhard bar or Watt's link, it's possible to get the rear tires to carry more of the load so the rearend will stick longer.
A torque arm is like an extra-long traction bar, as it lifts the chassis near the center of gravity, making available all of the car's sprung mass for transfer to the center of the rear axle, distributed evenly to both rear tires. It also controls rear axle brake torque and therefore increases antilift at the rear, making the rear brakes more effective.
According to Griggs Racing, "This has the effect of increasing rear traction while decreasing stopping distance by reducing forward weight transfer under braking. It does all this while at the same time making the car much more controllable and easier to drive hard in a corner, especially in corners on uneven surfaces or cresting hills, or when launching on poor surfaces, eliminating the 'white-knuckle ride,' even in the rain."
Yet another way to improve your Mustang's handling is with the 5-Link designed by Steeda Autosports. The Steeda 5-Link suspension was bred through extensive track experience and testing, and is said to offer a roll-center reduction, positive lateral control, improved antisquat geometry, increased traction, and better dynamic stability. It consists of a Panhard bar, and two longer upper control arms that utilize different geometry to accomplish the same task as the stockers, but in a better manner.
Steeda's latest 5-Link 2 features improved compatibility with tailpipes, easier access to the differential for service, optional bolt-on installation, and compatibility with Steeda's adjustable rear sway bar and rear coilovers. Steeda claims the 5-Link has better antisquat geometry than a torque arm and less corner-exit understeer.
The 5-Link's upper and lower links work together to create an instant-center geometry, which moves in response to suspension loads. During acceleration the instant-center moves rearward to counter the effects of chassis squat. During braking, the instant-center moves forward in response to chassis lift, lengthening the side-view swing-arm to reduce the possibility of wheelhop that's likely to occur in a torque arm-equipped Mustang. In our own testing, we've noticed the 5-Link offers better ground clearance than a torque arm. We suggest you talk to people who run both systems and get their opinions. Also consider whether it's a Fox or SN-95 Mustang, your vehicle weight, tire choice, and general vehicle use before selecting one.
The Watt's Link
The Watt's link has been around for a long time, and it has most recently been seen beneath Saleen's '07 Saleen/Parnelli Jones Limited-Edition Mustang. This Pony was engineered with Saleen's Racecraft precision suspension, including the new race-derived Watt's link suspension.
The stock S197 Mustang suspension includes a Panhard rod and sway bar. While it's a good suspension system, it provides Mustangs with some unwanted characteristics associated with the suspension setup, according to Saleen. The biggest disadvantage the company sees with the stock setup is that as the suspension travels up and down, the axle travels in an arc and moves side to side in the chassis, which introduces unwanted lateral forces to the suspension.
"The Watt's link greatly improves the feel and handling of the car," says Bill Kreig, chassis systems supervisor for Saleen. On the track, it handles as if it has an independent rear suspen-sion, staying firmly planted through the corners. On the road, it produces a more stable and comfortable ride than the Panhard rod on high-speed/high-frequency roads, especially on California's bumpy freeways.
"The Watts link suspension works to improve the ride and handling of the Mustang by minimizing the rear-axle lateral movement, optimizing the roll center, and adding four directional bushings to the Watt's link. The pivot point is mounted to the axle and works with rigid frame mounts to optimize the rear roll center, providing a balanced feel and maximum lateral grip. The Watt's link utilizes state-of-the art directional bushings, which differ in stiffness depending on the direction of the load being applied. These bushings are positioned to offer extra stiffness for lateral loads and less stiffness for vertical loads. This causes quicker weight transfer in corners, which allows for a quicker turn-in and offers a more comfortable ride. Working in conjunction with the sway bar, the Saleen Watt's link keeps the tires as flat as possible, creating better control, and has been proven to improve speed by 2 percent. Lap times on average were two to three times faster."
Springs are necessary to separate the chassis from the vehicle and allow the tires, wheels, and suspension to absorb imperfections in the road surface. Without springs, your vehicle would ride like a skateboard or shopping cart. You'd get a bouncy ride and the tires would have great trouble staying in contact with the road, thus causing a loss of control.
For many, changing the ride height of their Mustang is mostly done for aesthetic reasons, as most people prefer to close the wheelwell-to-tire gap. Once again, the factory has to meet myriad requirements that some of us are willing to let go of for the sake of appearance or performance. Lowering a car means using shorter-than-stock springs. This in turn requires a stiffer spring, and while that can help the body resist roll during cornering, too stiff a spring can cause the tires to skip and slide in the turns.
With aftermarket coil springs being such a popular modification, we went to Eibach Springs and asked a few questions regarding coil springs. Eibach's research and development manager, Phong Diep, handled our inquiry, and this is what he had to say:
Q: What are the three most important things to know when shopping for coil springs?
A: "The ride height the spring will set the vehicle at, the spring rate, and the quality of the spring."
Q: What's the difference between specific rate and progressive rate springs?
A: "Specific rate or progressive rate is usually determined by whether the vehicle has progressive or linear suspension geometry.Due to the linear geometry of the Mustang's suspension geometry, progressive spring rates are used."
Q: Can you give examples of linear or progressive suspension setups?
A: "In linear suspension geometry, the change in wheel movement and spring displacement remains unchanged throughout suspension travel. In a progressive suspension geometry or increasing wheel rate suspension, the change in spring displacement increases with wheel movement. This would make a linear rate spring seem progressive."
Q: Can you go too low?
A: "Yes. Ideally, you want the vehicle as low as possible to lower its center of gravity, however, as low as possible will leave nothing for suspension movement. There must be enough travel remaining for the suspension to absorb bumps."
Q: What effect, if any, does vehicle weight have on ride quality and spring-rate choices?
A: "You can determine the spring rates necessary to achieve the ride quality you want for any vehicle weight. Furthermore, each spring must have enough rate to keep the vehicle from bottoming out and provide the correct handling for the vehicle. Heavier vehicles will require more rate, however, there must be enough damping. The damper is another important element in the ride quality of a vehicle."
Q: How do dampers and coil springs work together?
A: "Springs and dampers work together to keep the tires in compliance with the road. The springs compress and rebound as the vehicle goes over bumps and dips. The damper controls the speed at which the springs compress and rebound to ensure the tires follow each bump or dip. The idea is to keep the vehicle moving at the intended height while the suspension moves to keep the tires on the road."
Q: Are different spring rates required for different suspension setups, and if so, what are the differences and why?
A: "Yes, there are different spring rates required for different suspension setups. If you're working with an available damper, whether an OE damper or aftermarket damper, you want enough rate for responsive handling and reduced roll but not more than the dampers can handle. Different vehicles will have different suspension designs. You may have suspension geometry that is increasing rate, decreasing rate, or linear."
Q: What do you look for in an aftermarket antiroll bar for stock springs and aftermarket springs?
A: "You must select the correct combination of spring rate and bumpstops to work with the available damper and antiroll bars. Of course, you can change your dampers and antiroll bars. You will look for roll bars with increased rate to help reduce body roll and control oversteer or understeer. Using aftermarket rollbars with stock springs will reduce body roll but keep the stock spring rate. The key is to have your entire suspension system performing at its best for either track or street conditions."
Coilovers, The Other Spring
Once thought of as a race car-only item, a coilover suspension is now far more common-place in the Mustang world. The stock '79-'04 Mustang front suspension design has the spring located between the control arm and the chassis, and while the handling of the car can be improved by switching to higher-rate springs, ride qual-ity begins to suffer, especially with rates over 850 lb/in.
A coilover kit allows installation of springs that provide wheel rates (different than spring rate) that are much higher than the wheel rates of an 850 lb/in spring that are left in the stock location. Higher wheel rates dramatically reduce body roll and brake dive, and improve steering response. The stock coil springs are also quite heavy compared to their coilover counterparts, as coilover conversion kits replace the cumbersome stock coils, with much more compact, lightweight springs that fit over the struts and shocks, hence the "coilover" terminology.
According to Maximum Motorsports' Chuck Schwynoch, this optimum spring location reduces suspension bind and unsprung weight, allowing the suspension to be far more compliant. This provides significant gains in grip because the suspension can more easily follow the road surface. Improved suspension compliance also drastically reduces impact harshness, resulting in improved ride quality, compared to any spring placed in the stock location.
"Vehicles being tuned for better handling will benefit from the higher wheel rates and the ride-height adjustment offered by a coilover setup," Schwynoch says. "Infinitely small increments of adjustment make precise corner-weighting a breeze, and Maximum Motorsports' coilover kits are available with a wide variety of linear rate springs for fine-tuning of the car's handling balance and the unique weight distribution of a particular vehicle."
You'll also find a lot of drag racers using coilover setups as well. Using coilovers provides a significant weight reduction in the place where Mustang racers need to remove it the most-over the front end. But you do tend to give up travel, which is a must for many drag cars. Schwynoch says coilovers increase weight transfer by providing bind-free suspension movement, and the ability of coilovers to allow precise ride height adjustments also aids in tuning the vehicle for optimum performance.
As with most performance parts, all coilover kits are not created equal, and you'll want to compare the features of each.
"We designed our threaded sleeve assem-blies to fit snugly on the struts and shocks," Schwynoch says. "The tight fit keeps the threaded sleeve from rattling on the strut. More impor-tantly, the lower spring perch is kept square to the strut and shock, reducing the chance of the spring bowing and rubbing on the threaded sleeve."
This is just one of the many reasons to do your homework before going out and dropping big coin on a hot suspension setup. No matter how good these setups are, they need to be optimized for each application. The various manufacturers can help you out with choosing the right shocks, struts, coil springs, and spring rates.
Since the unibody structure is the foundation for your performance vehicle, it must be strengthened to handle the increased loading and stress often encountered in performance driving. The Mustang aftermarket is chock full of components to accomplish just that, and what's better is that the parts are generally inexpensive as well.
Why does the chassis need to be stiff? There are a number of reasons. The chassis in your car was designed to provide a relatively rigid structure given the vehicle's power output, weight, suspension setup, and engineered crash structures. When you increase power and/or suspension stiffness, the added stresses are transferred throughout the chassis, and this increases the load or stress on the structure. Constant flexing could create chassis damage or misalignment of the suspension pick-up points. That's why drag racers tear out torque boxes, C-pillars crack at the roofline, and strut towers are tweaked out of alignment.
By stiffening the chassis, the main structure of the vehicle, you reduce flexing, and this in turn allows all parts to perform better. You get to put the power down sooner and harder, and your suspension will be more predictable.
The most common chassis modification Mustang owners make is subframe connectors. If you take a gander beneath your Stang, you'll notice there are framerails stamped into the chassis at the front and rear of the car. The problem lies in the fact that Ford never connected them (until 2005, that is), and in a rear-wheel-drive application, the chassis flexes right in the middle, which causes all sorts of problems. Subframe connectors tie the two sets of framerails together to make the structure more solid. There are quite a few types, from bolt-in, to weld in, to custom units that require the floor of the car to be sectioned out and the new rails welded into the structure.
Another popular modification is the strut-tower brace. This device was originally called a "Monte Carlo" brace because of its use on Ford Falcons used in European rally racing. This bar ties the two shock towers in the engine compart-ment solidly together, and they are usually triangularly fixed to the chassis firewall. Under hard cornering situations, the shock towers can flex (in and out), which doesn't allow your sus-pension components to do their jobs properly. Ultimately, having a stiff chassis will allow the suspension parts to move in and out or up and down consistently over time.
When applicable, the ultimate chassis stiffening modification is a welded-in rollcage. A properly installed cage, or at minimum, a rollbar, ties into critical chassis points to triangulate them, thus providing not only safety for the driver, but torsional stiffness as well. Beyond the roll-cage, a full-tube chassis can be constructed to replace the factory unibody chassis and support the body components and drivetrain.
Tires are an integral part of your car's handling package, and their numerous features can alter the handling tremendously. Things like rubber compound, sidewall stiffness, and tread design all change the characteristics. One of the most frequent things Mustangers do is put fat tires out back and smaller tires up front. Much of this comes from the musclecar era when staggered sizes were cool to have, but mostly we do it because power mods are the first thing we do and traction becomes an important issue.
"More rubber on the road will increase grip, but that's not always a good thing," says Schwynoch. Start by asking yourself if the handling is balanced, or does the car understeer (front loses traction first) or oversteer (rear loses traction first)?
"Let's say a car has the same size tires and wheels all around and the car has been modified slightly so that the handling is pretty neutral," Schwynoch says. "Neutral means that if you corner at 1.0 g and you speed up for a corner that you had been taking at the car's 1.0-g limit and try to take it at 1.1 g, then both ends of the car will lose grip, and the tires at both ends will squeal as the car goes into a four-wheel drift.
"If you increase the rear grip, whether by installing wider tires or by some other suspen-sion change, perhaps the rearend of the car now has the ability to corner at 1.2 g, but the front is still limited to 1.0 g. So, when you enter your usual corner and try to go through at more than 1.0 g, the front tires will lose grip, but since the rearend still has grip, instead of the previous four-wheel drift, the car plows through the corner nose-first.
"At this point, the car is still limited to cornering at 1.0 g, but now the balance of the car has changed from neutral to understeer. Most drivers will think that whatever change was made to the car was bad (and they will swear the car is slower), because it 'made the car understeer.' The fact is, the cornering limit is still at 1.0 g; it's just that the balance of the car changed, as it now has a disproportionate amount of rear grip relative to the front."
Tire stagger aside, the construction of the tire has myriad effects on the handling of your vehicle. Tread compounds, tread patterns, sidewalls and even tire pressures are all things to take into account when looking at improving the handling of your Mustang. The construction of the tire directly relates to its intended use so you need to have a clear idea of what you plan to use the car for in order to make the best choice.