Suspension Tech Guide - Part 3 - Springs and Lowering Your Mustang

One of the more commonly performed suspension modifications on a Mustang is lowering it. While there are a few ways to accomplish this, most people change the front and rear springs. Other options include the use of drop spindles or special K-Members, but those options are normally reserved for cars seeing some track duty, which will provide justification for the extra expense.

Most owners lower their cars to give it a more aggressive look, but you should also keep in mind how it will affect on the rest of the car. If not, you may find yourself disappointed with one or more aspects of your car after you’re done. It’s much cheaper, and the results are more rewarding, if you plan ahead and do things right the first time.

Choosing the correct spring can be a daunting task. The task can be made easier by simply examining your situation and your needs. There are a multitude of manufacturers providing aftermarket springs for the Mustang. A few of these manufactures are Eibach, Steeda, and even Ford. In addition to the manufacturers, you’ll also want to decide how much you want to lower your car. Each spring set will lower your car by a different amount, so after determining the desired drop, find options that fit your needs. You should make sure the spring is suitable for your application, as whether the car is a coupe, convertible, V6, or V8, will make a difference. Springs will be tuned for a certain weight, and will be intended for a certain type(s) of car.

Different spring options provide several options in regards to the spring rate. The lower the car, the more important the rate becomes. Your goals should also take into account what spring rate is ideal for your situation.

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 more of 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.

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.

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 the other categories.

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 that drag-springs allow the suspension to have a much fuller range of movement. This is due to a softer spring rate, and also has a side effect of cornering ability suffering. 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 assists the car in hooking up and getting the power to the ground.

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.

There are two types of springs to help accommodate the various uses of their prospective owners.

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 springs operate in a much different manner than standard springs. The rise in spring 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 200lb rate, and continue to increase from that point. Progressive springs find more of a use on the street. The fact that 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 travelling too far when necessary.

As you lower the front of your car, you are effectively changing the geometry of the whole front suspension. Various suspension angles and tolerances will change as the suspension moves up and down. From the factory, the car’s suspension is set in a neutral state that falls in the middle of this range. As you lower the car, however, you place its “normal” state outside of that factory range.

While most owners simply swap springs and call it a day, you should really take the time to consider what effect the swap will have on the rest of your suspension. The spring swap will change the way your suspension performs, and can prematurely wear other components or even worsen handling. Let’s examine some of the common issues, and how to solve them.

Bumpsteer refers to the toe angle of the car changing as the suspension travels in it’s up and down motion. This is due to the tie rods traveling at a different rate than the control arms. This is compounded by a rough or imperfect road surface that will cause the suspension to react. The result is a car that feels like it changes directions as it hits these imperfections in the road. At best, bumpsteer is a nuisance. At its worse, it can be dangerous on rougher roads and higher speeds.

This is accentuated when the car is lowered and its “normal” ride height has already placed the tie rods and control arms in a much different position than the manufacturer intended. The fix for this is a bumpsteer kit, such as those offered by Steeda.

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 larger amount of lowering involved, however, the more you may find yourself needing to enlist the help of camber plates for your front shock towers. One benefit of aftermarket camber plates is that most will also facilitate the ability to adjust caster angle as well, should you desire to do so.

Keeping the lessened clearance in mind, is one of the most important aspects of lowering your Mustang. Many driveways and parking lots may make lowering your car an unrealistic upgrade. So 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.

The roll center is found by using a pair of imaginary lines that would follow the control arms and intersect with one another. The goal of a perfect suspension is to keep this point and the center of gravity as close as possible. As you lower the car, this intersection point changes and alters the difference between these two points. The result can be increased body roll. The cure is a normally a thicker swaybar, however other options include ball joint and control arm relocator kits.

Depending upon the change in ride height and spring rate, you may want to investigate whether you need to replace the shocks and struts. The shocks and struts dampen the movement of the springs, helping to restore a more comfortable ride and keeping the suspension more predictable. With the myriad options of shocks and struts available, it’s a good idea to enlist the help of the manufacturer or vendor to properly match your springs with your shocks/struts if needed.

In 2005 Ford made some significant changes to the Mustang. The result, for those looking to lower the car, is a few other things to consider.

When changing from a four-link suspension to a three-link suspension, Ford used a panhard bar. This change results in an additional consideration for owners of these cars. With a panhard bar, as the rear axle rises and falls, movement is in a slight arc instead of completely vertical. This arc also comes into play as the car is lowered, and the result is that the rear end will shift slightly to one side as the car is lowered. The solution to this shift, is an adjustable panhard bar to replace the fixed length factory bar. This allows the rear end to be properly centered again, once the vehicle is lowered.

The three-link suspension can also affect the vehicle’s pinion angle as well. 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. To combat this, you want to look into an aftermarket upper control arm. You can choose between fixed length replacements, or adjustable options.

You likely now have more to think about if you were looking at lowering your Mustang. You could simply slap a set of springs under your car and do all right for yourself. But if you want to get the best results, you’ll have to evaluate several factors. It's always best to go into a task such as this fully informed, and even though you may spend a little more than you originally intended, the end result will likely be much more rewarding than taking the easy and quick way out.