This view is staged to simulate the position of the rearend in relation to the chassis at
Weight Distribution Initially, we had to move some weight to the front to get a better front-to-rear percent, to around 52-53 percent rear, so we moved a 30-pound piece of lead from the back of the car to a point at mid-chassis and at around shoulder height, next to the driver. This piece came from the rear bumper and should not have been located there for reasons of negative polar moment tendencies. Keeping your moveable weight between the axles is a design goal that has proven itself over and over again.
If you have a car that won't turn, putting weight or ballast far to the rear of the car will help the initial turn-in and middle by making the rear loose, but will make the car very loose off because there will be no bite once the rear tires have lost contact with the track surface.
The battery location in this car is excellent. It's mounted high and on the right side, in
J-bar Placement We mounted the J-bar to the right side of the chassis so that we could be more consistent. This is something we had done in the past on tracks with more bite. This drastically changes the attitude of the car in the turns and coming off the turns. We did a dirt test a few years ago and made this change in the process of making lots of changes. It did not help or hurt the lap times, but it did make the car much more manageable to drive. We maintained this configuration through the final race we won, but might reconsider moving the bar to the left-side chassis mount in future races.
Spring Rates We started out with more conventional spring rates up front using a 450 LF and a 500 RF. In the rears, we used a 425 LR (equal to a 212 on the birdcage) and a 450 RR (equal to 234). Remember, we're using the swing arms on both sides, and we calculated the motion ratio squared for the left side was 50 percent and 52 percent for the right. So multiply the installed spring rate by the percentage to get the rate the car "feels," or equal to a spring mounted on the birdcage.
In looking over Bobby's notes, I noticed that he changed the rear spring rates to 450 LR and a 400 RR. He noted that the car was "a little tight in the middle and off." The softer RR spring rate was now making the car tight. We would later return to a stiffer RR spring.
The lift arm system was reinstalled after we disengaged it at the beginning of the project
Mid-Season Progression As the season went along, Bobby made a few changes to various components to try to find a feel he liked and one that would provide more bite off the corners. A few crashes here and there caused some of the frontend settings to be altered. When we checked them, he reset them.
Caster and Camber In the final races, the caster split was set to 1.5 degrees LF, and 3.5 degrees RF. The cambers were set to 2.5 degrees LF and 4.5 degrees RF.
The team did take tire temperatures, but from my estimation, they cooled much too quickly from the time the car was making laps until they could get the temperature gauge on the tires. So the readings were very low. Nonetheless, adjustments were made based on those readings. We might check tire wear in the future to get a better idea of proper cambers.
One of the changes Bobby made was to move the right rear spring off the swing arm and onto
Also, if we get into more rear steer, which we did, the caster split might need to be closed up a bit to provide a more comfortable steer to the right as the rear comes around. With the caster split we have, it has to feel awkward to steer right against the split.
Lift Arm Reinstalled In the initial runs with the car, Bobby noticed that the pullbar was bottoming out. When it did, the car would snap loose. I'm not sure if he used the adjuster to tighten it to provide more resistance or not, but the decision was made to go back to the lift arm setup along with the original Rayburn single-spring pullbar. He then moved the pullbar 3.5 inches to the left of center for more forward bite. This placement puts more load on the left rear tire when the car is accelerating.