How fast a shock’s valves can move is also important. Slower speeds generally influence handling that has to do with turning and cornering, while higher speeds have more to say about how exactly it’ll handle bumps and ruts. A good shock is designed with multiple speeds and the ability to handle all sorts of different situations.
Single-adjustable coilovers feature compression and rebound adjustability that’s dependent on one another. Firm one up, for example, and you’ve done the same for the other. Higher-end, double-adjustable (or split-level control) coilovers allow compression and rebound to be manipulated independent from one another. Depending on the coilovers, adjustments can range from as few as eight clicks to as many as 32 positions. Coilovers with single-adjustable damping generally allow for low-speed rebound changes and don’t affect compression a whole lot. Nevertheless, on a properly set-up car, such coilovers can still improve handling. No matter the type of damping adjustability, changes can be made by an externally mounted knob (typically fixed to a shaft) and a spring-loaded needle valve, which controls internal fluid flow and, as a result, damping characteristics. Now’s a good time to mention that these sorts of damping adjustments typically won’t result in dramatic handling changes and are best left for fine-tuning and sorting out the right kind of chassis balance once the rest of the suspension is in order.
As important as shocks are, it’s the springs that absorb the bumps and control body roll. They do all of this by compressing and rebounding in the same way that a shock’s piston does, but they do so to absorb wheel motion. The springs stop the chassis from bottoming out, maintain tire control over bumpy surfaces, and they prevent body roll when going around corners. The springs also help reduce squat when accelerating and diving while braking. More obviously, springs determine a car’s ride height and, not so obviously, its center of gravity, which has a whole lot to say about how well a car will handle. Spring rates ought to be considered as carefully as shock damping: Choose something too soft and the shocks might bottom out; do the opposite and your tires will have a hard time doing their job.
Compress a spring, determine the pressure applied, and you’ve just figured out its preload. Every coilover’s spring should incorporate some sort of preload. Increasing it can result in a better tire contact patch, which can improve traction and cornering capabilities, but too much can make things worse. Any coilover that relies on spring compression to adjust ride height is dependent on preload, though, which isn’t always a good thing. Slip-fit coilovers and full-bodied coilovers that don’t feature adjustable lower mounts are victims of not being able to change ride height without adjusting preload. For street cars, though, which don’t spend a whole lot of time on the track, this is typically not a big deal. When setting up a new set of coilovers, introduce a small amount of preload to keep the springs from bouncing within their assemblies before installing them on the vehicle.
Coilovers, shocks and damping rates might seem mysterious, but they don’t have to be. Understand that no single suspension upgrade will make an otherwise crummy suspension all of a sudden ready for the racetrack, and you’ve just figured out much of what makes all of this seemingly mysterious in the first place.
Additional Bilstein Photography Courtesty of Elli Dolfo
Mono/Twin-tube illustration courtesy of http://www.theeuroalliance.com