With the final changes made, the car looked much better and felt like one Bobby could cont
The lift arm is much longer than any pullbar and provides lots of control for both acceleration, which we controlled with the pullbar, and for deceleration. We will be tuning this device in the future to improve our entry and exit performance.
Rear Steer Is Back Bobby also reset the link angles to provide more rear steer. Because we were still running the J-bar on the right-side chassis, the rear attitude in the turns was not what it would have been if we had mounted the bar to the left-side chassis. The left-side mounts cause the rear to raise up quite a bit more and enhance the effects of rear steer.
We probably will try a left-side J-bar mount in the near future to see how it works with the new link angles. Ultimately the LR forward (lower) link was 22 degrees up, the LR top mount was 20 degrees down, the RR forward link was 15 degrees up, and the RR top link was 9 degrees down. This provided some rear steer, and did help on the dry and slick tracks.
Final Weights For the final weights, Bobby added some rear weight and mostly ran a high range of crossweight, or left-rear weight. In talking with many dirt racers, most run the lower range of left rear, or around 65-75 pounds or so. The high range is upwards of 240 to 260 pounds of left rear. Here are our final weights and percentages. The rear percentage was 55.1, left-side percentage was 53.4, and the left-rear weight was 249 pounds.
Bobby being a big guy would have a hard time reducing the left-side percentage, but we may try doing that for the dry/slick tracks to get more load on the right-side tires. We might also change to a lower left rear weight and see how that does. If we move the J-bar to the left side of the chassis, we might need to put more load on the right rear tire for added bite.
Spring Rate Changes For the final spring rates, Bobby made a change to the right-side mounting of the spring. He moved the spring from the swing arm to the birdcage and changed the rate to 225 pound spring. Note that the "felt" rate of the 450-pound spring on the swing arm was 234, or very close to the one now installed. So the net change in spring rate did not change.
Bobby did change the left rear spring to a 375-pounder, or the equivalent as if it were a 187-pound spring mounted to the birdcage. This increased the spring split to a stiffer RR spring. I have found that over the past five years or so, many top Late Model teams are going to stiffer RR springs for some conditions and having a lot of success.
Other Changes Some of the other changes that were made include trying a different brand of tires, installing a new motor, using a new trailer, and wearing a new driver suit. Here are the details.
Tire Changes Mid-season, Bobby changed from Hoosier tires to American Racers. He says that the side walls were softer on the AR tires and he felt that he was able to get more side and forward bite as a result. We don't really know if it was a compound difference or side wall construction. We do know it made the car faster.
He also increased the rear stagger from 3.0 inches to 4.75 inches, and that made a big difference in how the car turned through the middle. He also started working with the grooving and siping adding more sipes to increase the heat in the tires.