In essence, a coilover is simply a shock with a threaded body atop which an adjustable perch and coil spring sit. Changing the height of the spring perch raises or lowers ride height at that corner of the suspension and, when matched with a progressive-rate spring, also alters spring rate. This adjustability allows precision tuning of a car's corner weights. According to Kyle Tucker, however, the primary benefit is the quality of shocks that are typically used in a coilover setup. "Adjustability is a coilover's claim to fame, so most are based on premium double-adjustable shocks," he explains. "Most entry-level shocks are a twin-tube design, which rely on fluid to absorb the motion of the springs. Unfortunately, the fluid can heat up after just a few laps on a road course, which reduces their damping ability. On the other hand, the monotube shock design utilized in most coilover arrangements uses both fluid and pressurized nitrogen for damping. In addition to dramatically reducing shock fade, a monotube offers a finer degree of adjustability."
For street machines that will see little to no time on an autocross or road course, coilovers may not be worth the bucks. On the other hand, if you're building a car that will be driven hard at the track, chances are that double-adjustable shocks and stiffer springs are already part of your game plan. If that's the case, upgrading to coilovers is an easy decision, since they cost just a hair more than a set of premium springs and double-adjustable (non-coilover) shocks.
If optimizing handling is all about controlling weight transfer and body roll, then achieving proper roll stiffness is of paramount importance. Roll stiffness is simply a suspension's resistance to body roll and is determined by the stiffness of the springs and sway bars. Some suspension tuners prefer using stiffer springs and smaller sway bars, while others prefer softer springs and stiffer bars. There is no consensus as to which setup is best. The pros and cons of each method should help steer you in the right direction. A setup with stiff springs and small sway bars allow the left and right sides of a suspension to perform more independently from each other, but compromises ride quality. Soft springs and stiff sway bars preserve ride quality, yet detract from a suspension's side-to-side independence.
Interestingly, all the suspension experts we talked to preferred soft springs and big sway bars. "I very much prefer a soft spring and a firmer sway bar," says Bret Voelkel of Air Ride Technologies. "The main job of the springs is to hold the car up, while the sway bars and shocks control the body roll. Throw in some adjustable shocks, and you will then have a wide range of control over ride quality and cornering performance tuning.
"I like using soft springs and stiff sway bars because it rides so much better," he continues. "Let's say you're using a 600-lb/in spring and you want to reduce body roll from 2 degrees to 1. To accomplish this without increasing sway bar stiffness, you'd have to double the spring rate to 1,200 lb/in, which would significantly degrade both ride quality and handling."
The leaf-spring rear suspension system used in many Chevy muscle cars is a primitive yet venerable design. It can be made to work reasonably well, but certainly has its limitations. Not only do leaf springs support the weight of the car, they also act as control arms by managing acceleration, braking, and cornering forces. The result is a compromised suspension design that doesn't do anything particularly well, which is only compounded by the obscene horsepower today's street machines are putting out.