Modified Mustangs & FordsHow To Chassis Suspension
Understanding These Points Will Keep Your Ford Pointed in the Right Direction
The next time you go screeching into a turn on your favorite freeway off-ramp, remember these handy pointers; they may help keep you out of the cheap seats. Numerous factors contribute to handling prowess, and in this short space well try to touch on the more important oneswhat upgrades you can make and whats most effective in terms of making your car handle like a go-cart.
By good handling, we mean a car that is the most controllable in the widest variety of situations, and for the purposes of our discussion, well limit ourselves to dry road circumstances. Needless to say, the presence of snow, ice, or water on the road calls for caution rather than experimentation in stretching the handling envelope.
The first point well discuss is tires. They can make more difference in your cars handling than any other single dynamic. All the killer shocks, sway bars, polyurethane bushings, and special springs wont help you much if you are still running around on pizza cutters. Well assume you know that radial tires are the way to go for the street, but beyond that, there are a lot of factors to consider.
The objective here is to achieve the widest possible contact area with the road surface. Common sense dictates that this maximizes adhesion, which is very important. This becomes of particular importance when any type of side-load is applied to the tire.
Side-loading is, of course, the immediate result of any change of direction (read: turn and, hence, handling). The sharper the turn, the greater the side-load on the tire. The larger the contact patch of the tire, the greater the adhesion that tire has, and the greater the side-load that can be tolerated. In other words, the larger your tires contact area with the road surface is, the tighter your car will corner without coming unglued. You must remember, however, that this rule applies only when the road is dry.
In terms of being cost-effective, dont skimp herebuy the best tires you can afford. They dont need to be Z-rated, but good tires contribute a lot to the overall safety of your car as well as those in it.
While its true that wider is better when it comes to handling, there are other tire-dimension factors to consider. You may know that when it comes to buying tires, the lower the series number, the shorter the sidewall. For example, a 225/50-15 size tire will have a shorter sidewall than a 225/60-15. The 225 refers to the tires width in millimeters; 60 refers to the aspect ratio of the tire, or the sidewall height in relation to tread width; and the 15 represents the wheel diameter.
The aspect ratio of a 50-series tire signifies that the sidewall is 50 percent of the tread width; on a 60-series tire, the sidewall is 60 percent of the tread width; and so on. The shorter tire is more desirable in terms of handling because of reduced deflection of the sidewall during side-loading or hard cornering. Beware of the trade-off here: While a shorter sidewall improves handling, it also offers less shock-absorption area between the tread and rim. Consider this if your car will be street-driven much of the time. We have 50-series tires on one of our Mustangs and have had to replace the tire-and-wheel assembly after hitting a pothole because of the tires shallow profile. While great for the track and for handling, the tires short sidewall depth didnt protect the rim enough to prevent serious damage.
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If you use anything shallower than a 50-series tire for the street, shock absorption becomes more of a problem. Tires in the 60-series range help a great deal when you're battling the urban jungle, and they're a good compromise between handling and street durability. Sure, Corvettes and Porsches come with 40- or 35-series tires, and they handle great, but for their owners, cost is less of a factor. These are expensive cars that are designed from the ground up with handling performance in mind. You can go buy one of these cars and be a cornering hero. Getting your '69 Mustang or '64 Fairlane to corner adroitly is another matter. It's more of an art form, and you can do it.
Another area of importance in handling prowess is suspension. We must assume that your front and rear suspensions are in excellent or at least very good repair. We cant discuss improving your cars handling if the ball joints are shot, because improvements elsewhere wont overcome worn ball joints or bent control arms. Certain things must be intact before we proceed. You should be able to properly align the car before we begin.
Many front and rear suspension components can be replaced to enhance your cars cornering ability, and you can use these to come up to alignment standards. When upper and lower ball joints are good, bushings on both the upper and lower control arms can be replaced with hardened units. These are usually polyurethane bushings, and while almost as hard as a rock, theyre great because they substantially reduce deflection.
One thing to be aware of when considering polyurethane bushings is that they can squeak. While this isnt a problem in a race car, itll drive you nuts on the street. Grease fitting are available to keep the bushings lubricated, and theyre the way to go for a street-driven car, though youll have to relube them sometimes after driving in a hard rain. Polyurethane bushings transmit more road and engine vibration than stock rubber bushings. The stock bushings can also be used to replace worn bushings if vibration abatement is a concern. When brand-new they work well, though not as well as the hardened bushings their major drawback being susceptibility to oil-induced deterioration.
Most cars within the sphere of our discussion came equipped with a front antisway bar and sometimes a rear sway bar as well. These are very important for reducing body roll. Body roll occurs in corners, where the body deviates from the plane parallel to the surface of the road. This deviation causes the body of the car to roll toward the outside of the turn. Centrifugal force comes into play here: The faster the vehicle speed is, and the higher the center of gravity on that vehicle is, the more profound the roll is.
Not only does body roll make passengers very uncomfortable, it tends to reduce weight on and ultimately raise the wheels on the inside of the turn. The faster you go, the higher the body on the inside of the turn travels, with the amount of weight on those inside wheels decreasing. Less weight equals less adhesion. Go fast enough, and the wheels lift off the groundleaving no adhesion. We dont need to explain how this hinders handling.
Antisway bars tie the suspension memberscontrol arms or axlesto the chassis. This helps keep the bottom of the body parallel to the surface of the road when in a corner. Since the axles (real or imaginary) are parallel to the road surface as long as the wheels are on the ground, it isnt hard to understand why antisway bars are effective. The thicker the bar, the more resistance it offers to the force of the roll. The use of these bars is one of the most effective weapons we have against body roll.
There are different schools of thought on the use of rear sway bars, and some folks will tell you that no rear bar is the way to go. On our 66 fastback, we have a bar of moderate diameter and find that it helps in high-speed sweepers. This is on the street, however. Applications for the racetrack may be different. The use of a rear antisway bar tends to be a personal choice.
Good shock absorbers are needed to make all of this other stuff work up to its potential. They control the up-and-down travel of the cars suspension after a bump or a pothole. Dont select shocks that are too stiff, or your car will hammer like a garbage truck over slight road imperfections. Shocks too soft will feel like grandmas sedan. Shocks that are too soft at high speeds make the car ride like a baby carriageslowly wallowing up and down with each undulation in the road.
And while were discussing shocks, lets address the topic of air shocks. We know some of you are running air-adjustable shocks out back. These can be great while compensating for additional loads and keeping things level. However, one problem with air shocks is that they can actually contribute to body roll. They do this in a corner by allowing air to transfer back and forth between shocks. The shock with the greatest load will force air into the shock with the lesser load and, in doing so, contribute nothing to the cause of minimizing body roll. The solution to this is quick and obvious. Install a separate line kit for each shock so the air in it remains locked inside.
One word of caution regarding the use of air shocks: Early Mustangs and other Fords featured unibody construction and were not really designed to work with air-adjustable shocks. Unibody cars have no heavy frame with brackets to receive the upper end of the shocks. There are holes in the rear floorpan, behind the backseats, to receive the upper end of the shock. These mounting holes are not reinforced.
If you install air shocks, pump them up, then load the car with a lot of weight, youre asking for trouble. Why? Because all that additional weight is resting only on tiny shock bushings, just under the little holes in the sheetmetal. If you hit a bad bump loaded like this, those air shocks are going to come up right through the floor. The resulting damage will be substantial and difficult to repair. Instability with air shocks is your greatest concern.
Exhaust-shop guys tell us they see this all the time on early Mustangs. The air shocks on our car had huge washers and doughnut-style bushings on top to reinforce this area and keep us out of trouble. Never overload your car and expect air shocks to keep you out of trouble. The air shocks were eliminated in our Mustang when new springs were installed.
If your vehicle is older, you may want to consider spring replacement. In addition to the factory replacements, you have many aftermarket choices. Lets choose a 65 Mustang for our example. This way well all know what were talking about, specifically a coil spring front suspension and a leaf spring rear. And were talking about a car thats nearly 35 years old.
Starting at the front, installing new springs can make a significant difference. When you combine them with all the other goodies weve talked about, you wont believe youre driving the same car. The same logic that applies to shocks applies to some extent to spring choice. Choose springs with too high a spring rate, and youll be hammering away again. Choose too soft, and youll lose the feeling of control youre after.
One friend we have chose Shelby GT350 springs for his ride, and we think the car rides too rough for the street. While great for a racetrack, where conditions are uniform and smooth, stiff springs can be bothersome on the street. Rather than the springs absorbing the shock, the car literally bounces over bumps. Every texture in the road surface is amplified, and the car becomes uncomfortable to drive after only a short time. We dont advocate a C-code granny rig selection, which is where we get into the baby carriagefeeling again. Choose something in between, and youll get both good handling and a reasonable ride quality.
Aftermarket springs allow a greater selection than stock choices, although we tend to think new GT springs on an early Mustang make a good choice. Out back, a similar set of rules apply. If you choose a moderate spring rate, you'll get the best of both worlds. One benefit we realized was that once we replaced the rear springs with new ones, air shocks became unnecessary. Even with two guys in back, the ride height was still within spec. We were surprised by this, which goes to show how much springs wear even though they look fine.
While we're on the subject of springs, we want to talk for a moment about ride height. A lower ride height has one major advantage in handling prowess. It lowers the center of gravity of the car. The lower the center of gravity, the less body roll is experienced for a given corner at a given speed. It's just that simple. That a little lowering improves the car's appearance is just a happy bonus. You can choose springs that will affect your Ford's ride height, so be aware of this when selecting springs. Don't lower too much, because the moment you get into problems with tire and ground clearance, you have a whole host of new problems. Work these problems out before you plunk down the cash.
There are many more advanced methods for enhancing handling, but these can be expensive and involve modifications that would make the car even more unsuitable to daily street use. Changing the suspension geometry, wedge kits, and humongous tires are outside the scope of this short discourse. Suffice it to say that a 65 Mustang can be made to handle as well as anything out there. Mustangs of the 6573 vintage lend themselves well to these types of handling upgrades. The best trick to all of this is to get everything to work together in handling harmony. Balance is the key to good handling, and choosing your chassis and suspension components carefully will help you win in the end.