In years past, racers have reacted to excess wheel travel at the RF by increasing the spring rate at that corner. This made perfect sense then, but in reality served to compound the problem.

If our setup is unbalanced, with the rear suspension trying to roll more than the front, excess weight transfer takes place at the front of the car onto the RF suspension. The increased weight causes more travel in the RF suspension. The imbalance between the front and rear suspensions is caused by, among other things, the wrong spring rates at the four corners. If the front spring rates are too high in relation to the rears, the car may be unbalanced, causing excessive RF suspension travel.

When we stiffen the RF spring, we have gone in the opposite direction we needed to in order to solve the original problem. What we should have done was soften the front springs rather than stiffen either one of them. I have seen teams soften the front springs and actually see less shock travel at the RF corner when this change served to balance the two suspension systems.

On flatter tracks, we can stiffen only the LF spring rate and achieve a similar effect. Due to the effect of downforce from the track banking, an increased roll effect is created that can help match the desired front and rear roll angles, a topic that we have covered in the past.

On the higher banked racetracks, we can run even springs across the front or successfully run a stiffer RF spring. This is especially effective when the banking for the turns rises up abruptly and we need a stiffer spring at the RF to control wheel movement at that transitional point. We would adjust the rear spring rates and moment center height to correspond to those changes.

When racing on flatter tracks, we often need to run a softer RR spring rate so we can help increase the amount of bite off the corners. Some teams will go to extremes with this spring split and end up with 25-50 pounds of spring rate difference, the LR higher than the RR spring rate. Most of the time, we do not need a high amount of spring split to achieve the desired effect. I have set up winning cars in major series on flat tracks while using only 10-15 pounds of spring split.

It is hard to balance the front and rear suspension systems when using a high amount of rear spring split, so we try to go with as little as possible when attempting to gain bite off the corners on flatter tracks.

On the higher banked tracks of more than 12 degrees, we can run a rear spring split with the RR spring rate higher than the LR spring rate to help balance the front and rear suspensions. This helps to control the rear roll of the car so that we do not need to raise the Panhard bar to excessively high levels.

It is common for a team to buy a new car from a different manufacturer or move to a new class where the cars are constructed differently. What often changes is the installation ratio at the front of the car.

Suppose we have run a class using stock spring rates at the front with stock lower control arms, and now want to run a class that uses coilover shocks and springs that are mounted differently on the lower control arms. If we have the setup figured out on the old car as far as wheel rates are concerned, we then need to duplicate those wheel rates (assuming the overall car weights remain about the same) in order to stay on track with our handling.

To do this, we need to know how to calculate the wheel rates in each car. We first work out the old wheel rates and then try different springs in the calculations until the new car has the same wheel rates. If we are going from a perimeter car (symmetric from left to right sides) to an offset chassis, the problem is compounded.

Wheel rate is determined by using the installed ratio (the position of the spring on the control arm) as well as the angle of the spring in relation to the line between the center of rotation of the ball joint and the inner pivots of the control arm. The motion ratio is the distance from the inner pivots to the center of the spring, divided by the length of the control arm. We then square the motion ratio number. The "motion ratio squared" number is then multiplied by the square of the cosine function of the spring angle, and that answer is multiplied by the spring rate in pounds per inch. The result is the wheel rate at that corner of the car.

Wheel rate is determined by using the installed ratio (the position of the spring on the control arm) as well as the angle of the spring in relation to the line between the center of rotation of the ball joint and the inner pivots of the control arm. The motion ratio is the distance from the inner pivots to the center of the spring, divided by the length of the control arm. We then square the motion ratio number. The "motion ratio squared" number is then multiplied by the square of the cosine function of the spring angle, and that answer is multiplied by the spring rate in pounds per inch. The result is the wheel rate at that corner of the car.