by Ruth Wolf

The function of the spring shock assembly in a modern race car is to keep the tire in smooth contact with the road. Even a small amount of weight transferred from a tire already on the edge of adhesion will cause a driver to loose control.

With good spring, shock and tire set up track irregularities will be absorbed so that a steady vertical force on the tire is maintained over a variety of road surfaces and loading forces.

SPRINGS

Springs determine ride height.
They control the amount of weight transferred, proportionally front to rear.
They are what keep the tire in contact with the road.

Spring rate is measured in pounds per square inch. It is the force needed to compress a spring one inch. A 200 pound spring will deflect one inch if 200 pounds are placed on it, two inches if 400 pounds are placed on it.

Spring rate is effected by many factors. Determining how much the suspension will deflect under load entails calculating the entire suspension geometry picture of the car in roll. The formula is spring rate = motion ratio squared divided by the wheel rate.

As drivers we need to be able to feel and react to the cars balance and understand how parts interrelate.

Spring rate combined with ride height should be established first.

Start with as soft a spring as possible to maximize tire contact with the road surface. The tire should roll over irregularities, instead of bouncing, without excess pitch motion - too much dive when braking or squat under acceleration.

Soft springs absorb more energy. They give the driver more time to react to bump and chassis changes. Bumpy tracks require softer springs, also use them on slick surfaces and for rain set up. But too soft a spring allows excessive body roll, and can bind up the front end causing bottoming out.

Test to determine what works well for your car for a given track and keep notes. Check during hard braking at the bumpiest corner of the track. Use stiffer springs for smooth, sticky tracks and to make car react quicker.

TIRES also act as a spring. How much bump is transferred to the suspension depends on how much is absorbed by the tire. The tries spring rate is determined by tire pressure, it construction and compounding. As the tire heats up it becomes stiffer, transferring more energy to the spring and suspension. If the spring rate is too stiff, it will get stiffer.

BUMP RUBBERS act as an auxiliary spring to keep the car from bottoming on a very bumpy corner, where you do not want to use a stiffer spring overall. They soften the force when the spring is fully compressed and the car is scraping the road surface, to allow the use of a softer spring for better mechanical grip elsewhere. They also keep the car from bottoming at speed due to aerodynamic downforce.

Bump rubbers are composed of polyurethane. Their shape and compounding determine the amount of deflection.

SHOCKS

Shocks control the energy in the spring and the timing of the release of this energy.

When the spring is compressed the energy of the initial motion is stored and released back in the opposite direction. The shock absorbs, or dampens this release of energy. Without them the car would oscillate uncontrollably. Just take a look at what is driven on the public highways.

A well-balanced spring-shock system keeps the chassis steady and in constant contact with the road surface.

Shocks only work when weight is being transferred. They have no effect in steady state running or cornering when there is no suspension travel. This is rare.

When the suspension is in transition and the shock is extended (rebound) or compressed (bump), they effect the car's handling.

Shocks are attached to the car's suspension so that the damper shaft moves when the suspension moves, and to the car's chassis. When the driver responds to the car's movement, the driver is responding to what the shock is doing.

Compression controls the motion of the unsprung weight. Rebound controls the motion of the sprung weight.

If the car has too much shock the ride will be harsh and will not absorb road irregularities. Too much bump and the car slides, rather than sticks; too much rebound and the wheels will not return quickly to the road surface and the car may "jack down" over long corners.

Soft shocks allow the suspension to move fast enough to keep the tire in contact with the road. But too little shock and the car floats, oscillates, dives, rolls and feels generally unresponsive.

Jacking down is a situation that occurs when the shock, after hitting a bump and compressing the spring, does not allow the spring to return to its neutral position before the next bump.

Repeated bumps will lower the car, there will be a dramatic increase in roll stiffness and the car will understeer or oversteer depending which end is effected. Adjust for bump (compression) first.

Bump controls the upward movement of the suspension when hitting a bump. It should not be used to control downward movements, roll or bottoming. Bump is set when "side hop" or "walking" in a bumpy corner is minimal and the ride is not overly harsh. The car should feel positive on turn in. If bump is too soft the nose will dive under braking.

Rebound adjustments has the greater effect on the drivers feel of the car. Rebound controls roll and lean when entering or exiting a corner and limits how fast the motion occurs. Rear shock rebound effects corner entry, front shock rebound effects corner exit.

Set rebound for smooth entry without excessive leaning. The driver can set the rebound for their preference of oversteer or understeer in corner entry without effecting corner exit.

Too much rebound will cause initial loss of lateral acceleration (understeer or oversteer depending which end) and will lead to jacking down. Shocks will control the timing of this motion.

Shock rates are a measurement of resistance, determined by the movement of the piston inside the shock body. Stiff shocks slow down the motion and speed up the rate of transfer. Soft shocks allow the suspension to respond quickly and slow the rate of transfer. The total amount (weight) transferred is determined by the spring.

ROLL BARS

Use roll bars (or, more accurately, anti-roll bars) to limit roll during cornering. Under cornering loads, the car rolls to the outside and compresses, the inside extends.

When this happens, the roll bar is twisted creating resistance to roll. Adding stiffness limits the weight transfer. This will also help keep excessive positive camber from occurring to the front tires.

Check the linkages and mounts. All rubber should be eliminated and solidly mounted to provide the most direct acting roll resistance. Any slop or looseness will cause the car to feel imprecise. On corner entry the car will roll before the bar restrains the motion and then the weight will accelerate and catch up to the bar with a thud. On corner exit there will be a dead spot until the bar catches up with the car, and then snap.

Remember as the driver you will be responding to the stiffer end of the car. Set up with front roll resistance stiffer than read for a solid feel during cornering and corner exit.

Still looking for feedback from drivers with front drive cars, circle track and drag racers. I'll be looking for your feedback, your experiences, and techniques that have worked for you. Respond to the discussion group at

ThunderValleyDiscuss@listbot.com