When designing the suspension and ride characteristics of most factory cars engineers are primarily concerned that grandmothers won't spill their coffee or complain about poor ride quality. The result is that most stock vehicles are outfitted with extremely soft spring rates that provide a cushy ride quality but offer little in the way of optimized cornering ability or weight transfer. And most don't look all that cool either, unless you're into four-by-fours.
Let's face it; most street machines look better when they feature an in-the-weeds stance. It lowers the center of gravity, gives a better road feel, and makes the car more stable without excessive body roll. However, trying to achieve even a 1- or 2-inch drop while retaining excellent ride quality can be a difficult task, because balancing ride height and ride quality generally involves making some compromises. We've all seen the results of hack jobs that were accomplished by either heating or cutting coils with a factory spring. That's the worst-case scenario-ride quality suffers and you can end up with a car that eats tires for lunch and is dangerously unpredictable on bumpy roads. That's not what you want.
Aftermarket spring manufacturers spend endless hours researching various combinations, which eliminates the guesswork and saves you bucks. So if you've been contemplating cutting or heating your factory coils instead of purchasing a matched set of aftermarket springs, read on to find out how to select springs to achieve the look and performance you want.
How A Spring WorksA coil spring is nothing more than a steel wire that's been wound into a circular coil. Minor changes in the overall diameter of the wire used, the number of coils that are wound, the free length of the spring with no load on it, and the outer diameter of the coil itself all significantly affect the characteristics of a coil spring.
Most springs are rated in pounds per inch (lb/in), which represents the amount of force required to compress the spring 1 inch at its installed height. A spring rated at 500 lb/in will compress 1 inch for every 500 pounds of force exerted on the spring. Compressing the spring 2 inches would take 1,000 pounds of force with a linear spring.
Since all cars will vary in weight, springs will also have various spring loads. To produce a certain spring rate for a specific car, the spring needs to first compensate for the weight of the car itself.
Linear vs. ProgressiveA linear spring has the same spring rate throughout its compression range. Progressive-rate springs have a variable spring rate that increases as the spring is compressed. The advantage of a progressive spring is that it can provide a variable ride quality-softer when the suspension is at a normal ride height, and stiffer as the spring is compressed, such as when the suspension is being pushed hard through a corner.
What Not To DoWhile most gearheads believe that lower and stiffer is better, the majority of suspension manufacturers will argue that it's the exact opposite.
The main advantage of having a car lowered is to increase stability by creating a lower center of gravity, but this doesn't mean it's OK to have your car resting on the bumpstops. With limited suspension travel, the car becomes unpredictable, skipping over bumps and road transitions and causing the tires to lose traction. While stiffer springs promote better handling, there is a limit. Using too stiff a spring will cause the suspension to bounce off sudden jolts. The purpose of a spring is to take a car smoothly over everyday road conditions such as potholes. If the suspension is so stiff or tight that it's not compliant, you'll be looking for a package plan from your chiropractor.
Heating vs. Cutting CoilsDon't heat a spring coil to lower your car. Period. Overheating weakens the spring material, causing unpredictable spring rates that can cause terrible handling manners and sag the car unevenly over time.
Cutting coils off of a spring is a different story. Some aftermarket springs come with additional dead coils that alter the free length, which only affect the ride height. Since these coils are not active in determining the spring rate, they can be cut to reduce the ride height without sacrificing spring rate. Factory coil springs, on the other hand, generally need all their coils to retain the spring rate. By cutting factory springs, you'll drop the ride height, but you'll also alter the spring rate, resulting in a stiffer ride. But you can usually get away with cutting about half a coil without adverse effects.
There's definitely a right way and a wrong way to cut coils. Be sure to cut a spring by using a high-powered saw that's able to cut through the coil within thirty seconds or less. Any longer than that creates the potential of overheating that can cause the spring to sag. Always cut in 11/44-coil increments so you don't go too far. This means you're going to spend a lot of time and effort fitting and refitting the spring, but it'll help prevent any dramatic changes that you may later regret.
When cutting a factory spring, you may find that the car occasionally actually sits higher at first. This is because the spring is getting stiffer as its live coils are cut. Continue cutting in 11/44-coil increments and you'll eventually reach the breaking point and get the ride height you're looking for. If you hastily cut in larger increments, you may go beyond the breaking point, ruining the springs and ending up with a car resting on its bumpstops.
Scaling Your CarScaling a car is the ultimate way to measure and adjust a vehicle's weight distribution. An individual electronic weight scale is placed underneath each tire and connected to a digital display that reveals the exact weight on each corner. By knowing the weight of the vehicle, you can see where you need to add or remove pounds to configure the vehicle for optimum traction. For open tracking or corner carving, you want the weight to be equally distributed. If your car weighs 3,000 pounds, the ideal setup would have each corner weighing in at 750 pounds.
During cornering, weight is shifted laterally to the outer tire. The more weight that is shifted onto the tire, the easier it is to lose traction. By knowing the car's weight at each corner, you can adjust the spring rates to help control the amount of force being transferred for maximum traction. Neat stuff, huh?
Drag vs. Sport vs. Open Track Spring RatesSpring-rate combinations vary according to the weight and intended usage of each vehicle. We asked Hotchkis Performance to recommend spring rates for three different types of driving use on a 3,400-pound '66 Chevelle packing a small-block. While these ratings only pertain to our imaginary example, they should give you ballpark figures on the type of spring ratings that are required for various applications.
Suggested Spring Rates Weight Distribution Usage Front Rear Front Rear Drag, straight-line performance 360 {{{100}}} 40 60 Sport, street car w/some corner carving 512 124-159 50 50 Open Track, all-out road racing 700 {{{200}}} 50 50