By no means am I a dirt track guy as you can spend your whole life studying tracks and such and still not hit on the right set up. Dirt racing is a black art and as much art as it is science. I have a hard-enough time getting things right on pavement so will just put in my two cents here.On Dirt, you do not want any rear roll over steer on a wet, tacky track. On hard packed dirt, yes, dial it in. That is why I recommend you know the chassis settings at ride height for zero roll steer, max roll over steer and a few settings in between.
4-Link Suspension systems use a Bird cage on each side of the axel that rotates around the axel tube. These bird cages have a top and bottom mount that mount radius rods to the chassis. Usually these are front facing as the pic depicts. Coil overs (sliders in some cases) are then mounted to the bird cage bottom mount on one side and dampers (shocks) are mounted to the back side of the mount. Sometimes the bottom mount attaches to a swing arm (Z link). We will study the more popular 4 Link suspension.
It became popular on dirt due to the ability to angle the top links upward where they attach to the frame mounts and use the tire thrust to load the tires. Any time the link is mounted uphill to the frame and the rear mount is downhill on the axel, the rear end will try to run under the chassis. This will load the tire bigtime. We have axel thrust.
Originally, these 4 links were designed to minimize rear steer during chassis roll. About 20 years ago, we wanted zero change in the wheel base as it was thought that this provided the most stable handling situation. Although it was thought that a small amount of rear roll steer would assist in turning the car but excessive amounts of roll rear steer was to be avoided.
Typical settings on 4-link was upper right link at 17° up hill,
upper left link at 13° uphill,
Both bottom links at 5° downhill.
This set up would add ¼ inch right side wheel base and reduce left side wheel base by ½” for ¾ inch rear over steer. Hardly noticeable.
As with anything having to do with fast cars, young women, and old whiskey, it was not long before some wild man started running more rear roll over steer than the next guy and now we have insane gobs of wheel base change and all kinds of body twist and shout!
Wild…
Now the wheel base changes up to 4 or more inches and we have link settings like
Typical settings on 4-link was upper right link at 18° up hill,
upper left link at 22° uphill,
Left bottom links at 5° Uphill. Right bottom level to the ground.
But a picture is worth me typing 1000 words and even more fun is watching this action.
This is rear over steer in action - Jake Bridge-Left rear dirt late model
2008 Hoffman Dirt Modified 4 link Rear Suspension with sliders torque link /damper
E-Mod on dirt Matt Stagman Rear Suspension Cam
Why you had better have that torque link and damper properly mounted
Modified 4 link camera on right rear. Cool index of bird cage. Tie down that brake hose!
Passmore Racing Dirt Late Model Torque Arm Video
I could watch this stuff all day...
