Well my first official post to a racing blog might as well be written as bounce down the road on the way to a race. Driving through a pouring rain makes racing tonight seem far from realistic, but we must press on. The race we’re heading to is in Kentucky, so the weather might be better the closer we get. We all worked for a couple of days putting some different ideas toward Dan Schlieper’s swing arm car. Although I have never seen this track, everyone else said the car should run pretty well there. I think there needs to be a little bit of back story on the car we are experimenting with to fully understand what is going on now.
When putting together a plan to build Dan a second car, He was running really well with a rear suspension configuration which we, in dirt late model racing, call a swing arm car. The left rear suspension is mounted to the axle via a bearing floated birdcage. It has one trailing arm going forward on the bottom and one linkage going backward on the top of the birdcage. Both trailing arms are mounted using spherical bearings to provide unbound motion of the axle vertically. The swing arm part comes in having the spring mounted to the front mounted lower trailing arm.
On the right side it is the same trailing arm configuration except, on our car, the spring is mounted on the bottom of the birdcage, just ahead of the axle. To control lateral movement of the axle a panhard bar mounted on the left side axle tube runs over the top of the drive shaft and connects to the chassis on the right side, just ahead of the spring.
Axle wrap is controlled by a spring loaded pull bar which is mounted on top the rear end center section and runs forward to the frame. The pull bar only works in one direction, as throttle is applied the top of the rear end wraps backward, compresses the spring, and exerts a downward force on the rear end, pushing it into the ground. Depending on the angle of the pull bar the car can experience quite a bit of anti-squat, or even lift, while exiting the corner.To control the unwrapping of the rear end under braking a long ladder bar runs forward from the rear end and hooks to a spring in the middle of the car via a chain. When the driver lifts off the gas and presses the brake, the slack in the chain, formed under acceleration, is eliminated and a force is exerted on the spring, cushioning the braking torque. The braking spring is commonly referred to a sixth coil.
The main difference in the new car Dan wanted built was the replacement of the pull bar with a fifth coil. A fifth coil is a spring mounted to the ladder bar just behind the sixth coil, up near the middle of the car. The other difference is a different style panhard bar mounted on the left side of the chassis and running over the top of the drive shaft to a mount on the right side next to the drive shaft yolk. This is what we call a j-bar. J-bars do tend to put more side bite in the car, but most drivers say they tend to take forward bit out of the car. The mounts for both the long right side panhard bar and the pull bar were left out of the car and the fuel cell was moved forward four and a half inches to cut down on the swinging moment of inertia of the fuel cell behind the axle.
Well, over the winter the panhard bar problem was solved by installing mounts to run both style panhard bars. The long right side bar was actually in the car when Dan set the qualifying track record at East Bar Speedway back in February. And now this week we installed a pull bar mount in the car. The pull bar gives the car more instantaneous traction whereas the fifth coil will seem to keep pulling the car further down the straight away. We also put a soft left rear spring in the car with a bunch of preload to help keep the tire contact patch loaded when the car rolls to the right.
Well, I’ll post tomorrow and update on how everything went.
Til next time,