3. Steering Geometry

Dirt car steering systems must be designed to work the same in both left- and right-turn attitudes. Mechanical effects such as Ackermann could be more beneficial on dirt than on asphalt, but again only to a small degree.

The Ackermann must be developed in the design of the tie rod angles from a top view and not differences in steering arm length. That way the wheels always keep the same toe or toe gain in equal amounts while turning right or left.

There will always be times when a dirt car needs to be steered right. In fact, most of the time, even with the "straight ahead" style, the steering will be turned more right than left. So, the steering box or rack must be centered with the wheels pointed straight ahead and the caster split should be minimal or even reversed from what we normally see for asphalt racing.

4. Alignment

Alignment issues present just as serious a drawback for a dirt car as with an asphalt car. There really is no reason to misalign the rearend. In tests we have participated in, we have run the same lap times with the car "sideways," due to excess rear steer to the right, as when running it straight ahead with no rear steer.

I believe that the rearend does not need to be any different in alignment than at 90 degrees to the centerline of the chassis and/or to the right side tire contact patches, and those patches need to be inline, even on dirt.

At the very least, a team needs to adjust the amount of rear steer in the dirt cars. There needs to be less rear steer for tight conditions and more for drier conditions. Most cars are built so that these changes are quick and easy.

So, study your system and learn how much rear steer is happening with each setting and make a decision as to which positions your trailing arms will need to be in for each track conditions in at least three different circumstances. Those would be 1) tight track with a lot of grip; 2) a transitioning track where grip is less, but it has not gone dry slick; and 3) dry slick to where there is very little grip and the lateral g's are much less.

5. Setup Balance

Does a dirt car really need to be balanced? Of course it does. The balance, though, will need to be adjusted for the track conditions. If the track is tacky, then the balance needs to be more like what we would do for asphalt and that is to match the desires of the front and rear suspensions.

The term Balance means that both ends of the car have the same tendency to roll. The truth about setup dynamics is that at mid-turn, each end will want to roll to its own degree of angle. The relationship between those desired angles will determine the balance of the car. On dirt we can manipulate that balance relationship to adjust the car to different conditions.

The setup for slick tracks is with a controlled difference in balance in the front to rear relationship with the rear desiring to roll more so than the front. This provides more rear traction to give us more bite off the corners. If our MC design is correct, the car should still turn through the middle, but have better traction off the slick corners.

Just as with rear steer, we need to develop changes to the balance in order to be ready for changing track conditions. A stiffer right rear spring will cause a more balanced setup for tacky conditions. Then as the track goes more slick as it dries out, the RR spring rate can be reduced to produce more rear roll and along with that, more grip for bite off the corners.

6. Shocks

Research on shock influences on dirt has shown that there are a lot of gains to be had by concentrating on your shocks. This is evidenced by the influx of new designs of shocks into the dirt car market. The age old truth is that we need to perfect our setup first before working with the shocks.

Dirt cars show a lot of travel as they negotiate the four turns. This extreme degree of wheel travel means that shocks get to do more work than with other types of race cars. A shock does not have any influence if it is not moving.

Each corner of the car might need a different shock characteristic. The amount of difference is directly related to the installed motion ratio of the spring and the spring's rate and amount of motion. A very soft spring would need more compression rate and less rebound rate, whereas a stiff spring would need a lot of rebound rate and much less compression rate.

Shocks affect the motion of the corners of the car and therefore the placement of wheel loads during transitional periods, and dirt cars are almost always in transition. That is the essence of basic shock technology related to handling influences.

Sometimes only one corner of the car needs to be adjusted in order to influence handling in the transitions. If I had a choice, I would make the RF shock the one to adjust for rebound and compression.

A stiffer RF shock in compression will tighten a car on entry. A softer RF shock in compression will help the car to turn in better. On the rebound side, a stiffer RF shock will loosen the car off and less rebound will tighten the car off.

For cars that are not allowed adjustable shocks, you can stock three or four different RF shocks to accomplish the same thing. Many shock companies will valve a non-adjustable shock the way you need them to be built. Label the shocks as "tight track," "medium track," and "slick track."