When you do your Ackermann check, this is a table to tell you how much added toe to expect
The first track test For our first test, we went to Concord prior to the race that was scheduled for that track. The setup was developed by me and I drove up to meet the team at the track. We got less than 15 laps in on the first try when our engine came unglued. It was taken back to Keith Dorton who personally oversaw the disassembly and assessment. After fixing the problem, the team reinstalled the motor and we went back to the track to resume the test.
After the first visit, we decided to make a change to the truck arm mounting. We had previously mounted the front of the arms in the top holes for minimum rear steer, but felt we needed more bite off the corners. We lowered the left truck arm to the bottom hole (of three holes).
The initial runs showed a very loose car at all points in the turns. The car was loose in, loose in the middle, and driving off was impossible. This led me to believe that there might be an alignment problem although the team assured me that the rearend had been squared.
A quick and easy way to check your alignment at the track is by using a string. You can me
We pulled out a string and put the steering box at center and locked the shaft. I noted right away that the right front wheel was pointed to the right. I had the team loosen the left and right-side tie rod adjusters and we aligned the right-side wheel straight ahead. We would toe the front wheels out using the left front wheel later on.
Once we had the right front straight, we looked at the right rear and noticed that it was toed or pointed right. We had already checked the rear for toe and it measured zero toe. This meant the RR was behind the LR and I decided to move the RR forward to align the rearend. We made two changes to the slugs and that produced a movement of 3/16 inch of the truck arm. That would result in a movement at the RR wheel of 0.250 forward and the LR wheel movement rearward of 0.137 inch. That is the equivalent of moving one wheel approximately 3/8 inch. Once the RR wheel was straight ahead to the RF wheel, we could proceed with the test.
The car was now more neutral in the turns. We did lower the right-side Panhard bar 1/2 inch, adjusted the shocks with less rebound in the RF and more rebound in the LF. We had a stability problem through the transition of the banking from Turn 2 all of the way to Turn 4. And, the car was very loose off Turn 2 and through the dip leading up to the backstretch. These changes made a marked difference and the car both looked good and was very comfortable to drive.
Here are the setup numbers after the test at Concord. The Panhard bar heights changed, but
Since the loose off condition was a transitional problem, we didn't want to make basic setup changes that would upset the middle of the turn performance. The only real adjustment we had was in the shocks. Joe Berardi with RaceWorks suggested a significant increase in the LF shock rebound settings. He thought that might make the car loose, but I disagreed and thought it might just solve the tight off problem. Here's why.
When the car accelerates, load is transferred from the front to the rear. The front of the car lifts when the load leaves it and this movement can be used to redistribute the loads on all four tires. Increasing the LF rebound takes a lot of load off that tire and distributes it onto the other three tires. This increases the load on the RF, LR, and RR. The overall load increase on the diagonal, RF and LR, causes the car to be much tighter by increasing the crossweight percent.
In subsequent runs, that's exactly what happened. The loose off condition was greatly improved and the overall attitude of the car going through the transitions was much better. Now we had a car that looked good, was quick and had even tire temperatures front to rear for each side of the car. The loose off condition was not completely fixed, but we were running on tires that had many heat cycles on them and the track was green and fairly hot.