In this right-side view of...
In this right-side view of the Z-link, downward chassis movement causes the right rear to move to the rear producing rear steer to the right.
If we just look at the way the car steers, we might conclude that this isn’t a very good idea. On asphalt this would produce a very loose car that would be undriveable. But if we look at the whole picture, including the aerodynamics of the body, we start to see why our lap times may be lower by doing this on dirt, especially on a very dry slick racetrack.
Winged Sprint Cars will generally run at an angle to the direction they are moving through the turns. The tall sides on the wing catch a lot of air and will produce a lateral force that is the opposite of the centrifugal force that tries to take the car to the wall. Long story short, the aero force counteracts the lateral g-force and helps the car go faster through the turns, just like having more tire grip.
The combined effects that raise the whole rear of the car also put the rear spoiler higher into the wind stream and that can produce more aero downforce at the rear. This helps give us more traction to
provide better bite off the corners.
If for each suspension system,...
If for each suspension system, the number “1” position produced minimal rear steer or movement of the axle at that side (which it should), then if we move from numbers 1 through 4, we would see more rear steer as the left side of the chassis moved up. The four-link left side view shows how moving the links up through the numbers produces more axle movement by causing the birdcage to move forward at both the top and bottom ends.
If the track has a lot of grip already, then we need much less rear steer and the associated aero help and so we make changes to our rear links so that less rear steer occurs. We may even benefit from creating opposite rear steer, to the left, to gain more rear traction, just like we do on asphalt. The operative word here is change. We must be willing to make changes and a more thorough understanding of what happens with each change will make it easier to do with better results.
What happens at many dirt tracks is that the track is wet and tacky as the day starts out. A car that is jacked up and rear steered to the max just won’t get through the mud as well as one that is more level with all four tires on the ground. We can position the links so that there is very little rear steer for these conditions.
As the track dries out and becomes more slick, we may need more rear steer and rear jacking to get the rear spoiler up into the airstream for more rear downforce and to drive the LR tire into the track. The rear steer has more effect on the angle of the body related to the direction that the car is traveling and an aero side force helps pull the car to the left to keep it from sliding. Putting more angle in the J-bar is warranted now.
The Z-link is a little different...
The Z-link is a little different in respect to the mounting holes because the top link chassis mounting points must be moved down to create the same effect. This shows how going up in number moves the wheel to the front aiding in producing more rear steer.
Once we fully understand how link angle changes produce rear steer at each side, we can make helpful adjustments at the track as the conditions change. We need to plan out which changes to make and be able to do them fast with little effort. A setup sheet that shows which holes to mount the links to for each set of conditions would help the crew make fast changes. If you don’t want your crew to know why you’re doing things (secrecy is an asset at times), then just number the different sheets and tell them to set the car to “Sheet 3,” period.
Because we need to adjust other parameters on the car for changing conditions, we can include spring rate changes, shock changes, and fifth- and sixth-coil changes as well when we make up the setup sheets. Once we develop our setup sheets, as we race the car, we can tweak the numbers according to the results. The process of dialing in the car to the conditions using our setup sheets may take a few races, but at least we’ll have a plan that takes us in a positive direction.