We now have a rolling chassis...
We now have a rolling chassis almost ready for action. We have bolted on all of the various parts and set up the car. Here is how we did it. Photo by Rob Fisher
Our Dirt Late Model project car has been undergoing a lot of change over the past month. We installed most of the body, all of the suspension parts, the rearend, and the motor and transmission. Now comes the fun part. We are ready to set up the car. As promised, here is a detailed summary of what we did and why.
We looked at where we were going to be racing and how our driver likes to race and tried to apply the technology we have been presenting in CIRCLE TRACK over the past few years. Fortunately, we have really good sources within the top levels of Dirt Late Model racing circles and we know how the top teams think and the way they approach their racing. We also know how it should be done technically and the two, practical application and theory, are on the same track.
Front Geometry
The first step in any first time setup is the front end geometry settings. We have already redesigned the front moment center location from what we had. Our MC was located, after dive and roll, at about 3.70 inches off the ground and 6.10 inches left of centerline. This is the dynamic location and the static location, the one at ride height, started farther left at about 18 inches left of centerline.
To get to those locations, we needed to drill new upper mount holes and then reinforce those holes with large washers welded on both sides of the square vertical tubing. We also installed Mono-Ball ball joints in both lower arms and spaced them so that the ball joints were as low as possible to take most of the angle out of the lower arms. This controlled our movement and location of the MC.
Before setting our front geometry,...
Before setting our front geometry, we needed to install links to simulate the position of the spindles to where they would be in relation to the chassis when the car is assembled, at ride height and with all of the weight in it.
We needed to set our caster, camber, and toe so we raised our car and installed links where the shocks mount that would simulate the spindle position at ride height with all of the weight on the car. These links can be made of any material, and we chose two strips of one-inch wide aluminum that would overlap. We clamped them with a vise grip plier and drilled a hole and bolted them together.
We decided on a caster split of 3.50 degrees positive caster for the RF and 2.50 degrees of positive caster for the LF. This provides some ease in turning left, but does not overly restrict turning the wheel to the right such as would be the case with a larger caster split.
The cambers we set were: LF = 2.50 degrees positive (top leaning out away from the centerline) and RF = 4.50 degrees negative (top leaning in towards the centerline). Because we will be setting this car up to be more balanced and using the left front tire more so than some setups, we did not need to put high amounts of camber in the RF.
We set toe with the steering rack centered and at 1/4-inch out, which we decided was plenty enough to stabilize the car. Some suggest higher amounts of toe, but we feel that those high numbers work best when the setup promotes a lot of front load transfer and the LF isn't working so hard. Once the LF is set up to stay loaded, high amounts of toe will work against being able to turn the car as the two front tires fight to go in separate directions.
Rear Geometry
We had already made the decision to take most of the rear steer out of the car, so when we mounted the rear links on this Z-link, swing arm car, we did so with that in mind. Both the upper and lower links are more parallel to the ground and with the bird-cage connection to the rearend provides wheel travel with little or no rear steer.