The suspension system must control body roll to make the tilt of the tires correct for cornering, keep the tires on the road surface over bumps and ruts, maintain handling balance, and provide nearly instant response to driver steering inputs. It's also important to maintain some ride quality so that your teeth don't rattle loose while you're going to the movies. To get to this pinnacle of performance handling requires sound engineering, strong R&D, and track-testing. Progress has a handle on this based on the performance of the Honda Civic.
The heart of a suspension system are the springs. Springs perform five critical jobs. First they keep the chassis and suspension from bottoming out over bumps. Second, they control the tires over bumps. Third, they control body roll during cornering, chassis squat during acceleration, and chassis dive under braking. Fourth, the springs determine how the load on the tires shifts during braking, cornering, and acceleration. This is a major factor in establishing the neutral handling balance of the car. And finally, the springs are the major factor in establishing the ride height (ground clearance) of the chassis. If springs are too soft, the chassis or suspension could bottom-out over bumps. The body can roll, dive, or squat too much causing the tire contact patch to be tilted relative to the road surface, which can hurt traction. If the springs are too stiff, ride quality is unacceptable for street driving and the tire contact patch can lose touch with the road surface over bumps and ruts. The series of compromises needed to create the ideal setup for a given car and performance application requires experience, sound engineering, and testing.
Sport springs should lower the car, which not only improves the look, but also lowers the center of gravity and improves handling performance. But if the springs are not stiff enough at the lower ground clearance, the chassis or suspension will bottom, causing damage. If the springs are too stiff, the ride is horrible and tire contact patch control over bumps deteriorates. The Progress Sport Springs provide a compromise between ground clearance, ride quality, tire control, and handling balance.
The next component in the food chain of handling performance is the antiroll bar. Antiroll bars control body roll, which helps keeps the tire contact patch flat on the road surface. They also contribute to the control of loading on the tires, which is a factor in handling balance. The front and rear antiroll bars are an excellent way to tune handling balance without affecting ride quality. The Progress AntiRoll System for the '88-'91 Honda Civic uses a 25mm front bar and a 22mm rear bar.
Next come the shock absorbers. Shocks control the bouncing of the suspension springs. Without them, the chassis would continue to bounce over bumps. Good-quality stock shocks can accomplish this reasonably well, but will fall far short when it comes to performance handling. Shocks play a major role in responsiveness and in transitional handling. Progress has developed its own performance shock for Hondas called the ProSport. The Progress ProSport is a twin-tube low-pressure gas shock specially tuned to work with the Progress Sport Springs and Progress Antiroll System. The compression and rebound damping rates of these shocks are considerably stiffer than stock. While the ride is firmer than stock, it is very acceptable considering the level of performance. These shocks allow precise and nearly instant response to driver steering inputs. The ratio of compression to rebound damping is ideal for quick turn-in and exceptional for transitional handling response, which we were able to experience first-hand on the straight line slalom. If the shocks are too soft, response is sluggish. If they are too stiff, the car is twitchy and rough.