The amount of Ackermann in...
The amount of Ackermann in our rack-and-pinion steering system can be regulated by moving the rack forward or backward in the car. This adjusts the top view angles of the tie rods to change the amount of spread that occurs between the ends of the steering arms as we steer the car.
In the rack-and-pinion steering system, if we have equal length steering arms (the arms that are attached to the spindle that the tie rods are bolted to) and still have excess Ackermann, we need to reduce the top view angle of the tie rods. We do this by moving and mounting the rack more forward. As we take the top view angle out of the tie rods, we reduce the amount of "spread" that occurs as we turn the steering wheel, and the outer tie rod pivots move rearward through the arc created by the steering arms.
A common fix, and one that is not recommended for dirt cars because those cars have to steer both ways, is to change the lengths of the steering arms so that one spindle will turn a different number of degrees than the other. If we have Ackermann present in our car, we can lengthen the left steering arm to slow that spindle down and/or shorten the right steering arm to speed that spindle up. Again, this only works to reduce Ackermann when we steer to the left. If we do this and then steer the car to the right, the opposite occurs and we gain toe because the right wheel will turn faster than the left wheel increasing the amount of toe-out.
On a drag-link system, we can move the drag link forward to reduce the amount of Ackermann for dirt or asphalt cars. On asphalt, the same quick fix can be used by lengthening or shortening the steering arms as discussed earlier with the rack-and-pinion systems.
3. Rear Alignment
We can change the amount of...
We can change the amount of Ackermann in our drag-link steering system in a way similar to the how we adjust the rack-and-pinion system. If we move the drag link forward in the car, we will take top view angle out of the tie rods and reduce the amount of Ackermann in this system.
If the rear end is not aligned properly, the car may be either tight or loose in all three phases of the turns. One of the very first tasks in setting up a race car is to make sure all of the alignment issues have been corrected. The rear end should be at right angles to the chassis centerline and the right side tire contact patches should be in line.
4. An Unbalanced Setup
A loose or tight car can also be caused by a tight or loose setup. These can be caused by an unbalanced setup, or by running the wrong amount of crossweight percentage. Tire temperatures can tell a lot about the setup and where we need to look to fix the setup balance problem.
If the average of the front tires is hotter than the average of the rear tires, the car is probably tight and may have too much crossweight percentage in it. The car should respond to a reduction in crossweight.
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. We need to maintain this setup balance as we try to fix entry and exit handling problems.
In the case of an unbalanced setup causing the 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 spring. That, too, will reduce the rear roll angle. We can stiffen the right rear spring and/or reduce the left rear spring rate, if we are running on a banked track of 12 degrees or more, to reduce the rear roll angle.
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. We can soften the right front spring, stiffen the left front spring or run a stiffer left front spring than the right front spring on flatter tracks. The stiff left front spring setup does not work well on tracks banked over 10 degrees. Changing to a smaller sway bar does increase the front roll angle, but not very much. We mostly use the sway bar to tune for traction off the corners.
5. Crossweight Percent
Crossweight percent is defined in circle track racing as the total of the right front and left rear wheel weights added together and divided by the total vehicle weight. If everything else is correct, such as alignment, balance, camber change, etc., and the car is still tight or loose, then the crossweight percentage is probably wrong for the weight distribution in the car. For a tight car, reduce the percentage of crossweight and for a loose car, increase the crossweight percentage.