The lift arm helps control...
The lift arm helps control the acceleration and deceleration forces in a dirt car. The more grip there is, the stiffer the arm's components need to be.
On dirt, when do we not need more bite off the corner? The exit portion of the track provides little traction, and most corners are usually more flat. We almost always need to develop more rear traction upon acceleration. To give the car more rear traction, we need to understand a little about the dynamics at work on the car.
We must develop ways to create more rear traction (on acceleration only) to avoid ruining our midturn handling. There are several ways to do that without changing the handling at other points around the racetrack. One way is to reduce the "shock" of sudden application of throttle and torque to the rear wheels.
We can use lift arms and pullbars with various stiffness of shocks and springs. More motion is needed for slick conditions and much less motion for the tackier conditions.
Another way to gain bite involves the use of a spring-loaded pushrod that allows a certain amount of right-rear wheel movement to steer the rear end more to the left. As the car accelerates, the right-rear wheel moves forward, creating a slight amount of rear steer to the left.
Antidive and antisquat are mechanical influences that can help our transitional phases of entry and exit. We can regulate the amount of both depending on the need.
A small amount of antidive on our dirt cars can help prevent sudden nosedive on entry by utilizing mechanical resistance to the downward motion of the suspension. We do this by using the rotational forces created through braking. Read the section named "The Anti's" in "Preparing for the New Season-Asphalt" (pg. 49) to learn more about how antidive works.
 A right-side spear rod, which...  A right-side spear rod, which replaces the lower trailing arm, causes the right-rear wheel to move forward during acceleration. This tightens the car off the corners while preserving midturn rear-end alignment. |  It's not that hard to weld...  It's not that hard to weld a new set of bungs to a dirt Late Model car. This way, the arm angles can be changed fairly quickly for different track configurations and conditions. |  Dirt cars have been modified...  Dirt cars have been modified over the years to a more wedged shape that directs oncoming air over the top of the hood and not under the car. This will produce some amount of downforce due to creation of low-pressure areas under the hood. |
Antisquat is the result of the pullbar trying to straighten out, or become more horizontal, as the car accelerates and the rear end desires to rotate. The more pullbar angle you have, the more antisquat there is. The lift arm also creates antisquat and can actually lift the rear of the car on acceleration. Lateral movement of the lift arm's front end (a result of acceleration) can alter the loads among the two rear tires.
The rear spoilers create drag...
The rear spoilers create drag and downforce. The extra lip, or "Gurney strip" as it is called in road racing, at the top of the spoiler curls the air up and away from the back of the spoiler, increasing its effectiveness.
Racers discovered the need for better aero designs some years ago. Just look at the dirt Late Model cars and how they have evolved. The front ends are wedges that scoop the oncoming air up and over the car. The wheelwells are shaped to route air out and away from the front tires, creating downforce.
How much you need to get involved in aero for your car depends a lot on what you run and where. Aero influence varies with the speed of the vehicle. There is an algebraic increase in both drag and downforce associated with increases in speed through air. That is why a car with twice the horsepower does not go twice as fast.
Try to understand how aero downforce is created and then configure your car so that you take advantage of every area where you could produce more downforce.On dirt, we need the most loading on our tires we can get, and aero-generated load is not weight we have to accelerate.
Dirt is a tough medium for which to set up. Get your car set up correctly for the basics of alignment and geometry. Plan your approach to the track on which you intend to run. As with all forms of motor racing, remember that success comes in stages. Improving your finishes is where you start on the road to winning. Don't think that just the work done to improve the setup will quickly lead you to Victory Lane. Learning how to win is a process, and when the moment is right you will find your way to the winner's circle.