The primary goal of all setups...
The primary goal of all setups is to develop a balance between the two ends of the car so that they will want to do the same thing in the turns. Once we find a balance that works through the middle of the turn, we need to maintain this setup balance as we try to fix entry and exit handling problems. The Big Bar and Soft Spring setups can be very unbalanced, causing big problems.
A loose or tight car can also be caused by a tight or loose setup. Either of these two can be caused by an unbalanced setup or by running with the wrong amount of crossweight. Tire temperatures can tell a lot about the setup and where we need to look to fix the setup balance problem.
In the case of an unbalanced setup causing a tight condition, the rear of the car wants to roll more so than the front. There are several things we can do to help balance the car. We can raise the Panhard bar to raise the rear roll center, which will cause the rear suspension to want to roll less. We can reduce the rear spring split if we are using a softer right-rear (RR) spring by stiffening the RR spring and/or reducing the LR spring rate.
At the front end, we can do a few things to cause the front to roll more to try to match the rear roll angle. If we have a much stiffer RF spring, we can soften the RF spring, stiffen the LF spring, or run a stiffer LF spring than the RF spring on flatter tracks. The stiff LF spring setup does not work well on tracks banked over 10 degrees. Changing to a smaller sway bar increases the front roll angle, but not very much. We mostly use the sway bar to tune for traction off the corners. With the BBSS setups, reduced roll angle is the goal, so using a smaller sway bar is out of the question.
There is a correct amount...
There is a correct amount of crossweight for every combination of setup and weight distribution for your car. If your car needed 51 percent and you run 52 or 53 percent, the car will be tight. There is no need to change springs to try to loosen the car. You need to lower the crossweight by taking cross or wedge out of the car. The correct procedure is to balance the car with some amount of crossweight distribution and then read the left-side tires. If the LF and LR do not have matching tire temperatures, start changing spring rates, moment centers, and so on to balance the car. As the balance is corrected, the crossweight must change with the other changes to maintain the handling balance.
With the BBSS setups, the front may want to out-roll the rear, causing excess load to be put on the right-rear tire through the turns. This happens when the crew knows there needs to be a spring split in the rear and installs a stiffer RR spring than the LR spring, but goes overboard and uses a RR spring that is much too stiff. When the LR tire is the coolest on the car, the rear spring split may be too much.
If all else were correct, such as alignment, Ackermann, setup balance, and so on, and the car was still tight or loose, then the crossweight percentage is probably wrong for the weight distribution in the car. Reduce the crossweight in a tight car and increase the crossweight percentage in a loose car.
A car can appear to be loose even though it is tight. This condition is very hard to detect from a driver's perspective. The car is loose right at mid-turn and off the corner. Sometimes the car is tight and the driver turns the steering wheel far enough to get the car to turn.
Because the front tires generate more traction with a greater angle of attack, the driver is actually putting more traction into the front end. The once tight condition now switches to loose as the front gains grip from excess steering angle. This happens very quickly and the rear end snaps loose as the throttle is applied. All the driver knows is that the car is loose. To correct this, we have to fix the tight condition to cure the loose condition. This malady is more common than most racers know.
The pullbar is just one device...
The pullbar is just one device that racers use to reduce "shocking" of the rear tires as the driver gets back into the throttle. The link is spring loaded and allowed to extend against the pressure of the spring to absorb some of the force of initial acceleration.
The entry and exit to and from the middle are affected by transitional components in the car. Transitional components include the shocks, rear roll steer, brakes, rear steer under power, camber change, rear stagger and the Anti's (dive and squat). Let's go through each item and explain how they can affect our turn entry and exit performance.
The overall rate and the layout of different shock rates on the car can greatly affect the weight distribution, and therefore the handling, in the transitional phases on the racetrack. If we are loose going into the corner, the LR shock may be too stiff in rebound or the RF shock may be too soft in compression, which transfers load off the LR tire on initial entry under hard braking. To fix this, reduce the rebound rate in the LR shock and/or stiffen the compression rate on the right-front shock.
If the rear end is positioned...
If the rear end is positioned so that it is aimed to the right of the centerline of the car, the rear tires will continually want to roll outside the front tires. This is obviously going to make the car very loose in all three of the turn phases. It is very important to align the rear end to point straight ahead and also to line up the right-side tire contact patches.
Try to install shock rates to complement the car's setup. Most top shock technicians will be able to help you select the proper shock rates to go along with your particular setup related to your type of racetrack.
Make sure your brake bias is tuned correctly. If too much of the bias is on the rear brakes, the car will be loose under heavier braking. If you lightly brake into the corner and the problem diminishes, then brake bias is the culprit. It helps to install brake bias gauges and then adjust the amount of pressure front to rear. Usually a 60-65 percent front and 35-40 percent rear bias works for most tracks.
Some rear suspension systems can be adjusted for rear steer. If the geometry is such that the rear end is made to steer on turn entry so that the RR wheel is farther to the rear than the LR wheel, we have rear steer to the right. This can make the car very loose and we need to adjust the suspension components so that it will not steer in this manner.