Take advantage of the off-season to refine your chassis setup with the top 10 most importa
Preparing the setup in a dirt car for the upcoming season involves some processes and knowledge of technology that has been developed over the past 10 years. The approach we advocate has resulted in a lot of success and made racing much more enjoyable for a lot of dirt teams. For obvious reasons, knowledge is not passed around freely in racing circles. No one is prone to let other competitors in on performance secrets.
The processes for dirt and asphalt are similar in some ways and very different in others. That is why we decided to split the story into separate articles so that we could speak to each group separately. As I said in the asphalt piece, if you read it first, the separation between these two genres is becoming both wider and narrower, depending on which aspect of chassis dynamics and tuning we are discussing.
You may need to go back to the asphalt article when some of that information pertains to dirt racing, too. So, all you dirt guys, just because you skipped the asphalt article and moved on doesn't mean you shouldn't go back and take in some of the technology presented in the asphalt piece.
On this dirt Stocker, we cut and lowered the stock mount to improve the upper control arm
For any race car with a double A-arm front suspension, we always start with the front-end geometry, be it dirt or asphalt. If the moment center design on your car is not set properly, then the whole car will suffer, no matter what setup you have in the car.
One of the primary complaints coming from dirt drivers is that the car does not turn well. The number-one reason for that is the front geometry is incorrectly designed. Just improving that aspect of the car's overall design can make a huge difference in performance.
The dirt car moment center design is different from that of an asphalt car. On dirt, the average g-force is much less than on asphalt because the track does not provide as much grip. So the MC needs to be located farther to the left in order for the car to work well. Trust me when I tell you that most top touring dirt Late Model teams have learned the importance of correct MC location. If not, then they are getting beat by those who do.
Monoball ball joints allow adjustment in height to change the angle of the control arm. Th
The dirt Late Model rear geometry layout is varied and highly adjustable. The car must be evaluated for where it is to be raced and then set correctly. The trailing arm angles affect the rear steer, and the pullbar or lift arm can redistribute load upon acceleration.
Many teams will tell you that there is a need for rear end steer to the right at times. A slight amount of rear steer to the left would probably improve lap times during tight and tacky conditions. But the use of rear steer to the left should only occur on acceleration and not at midturn.
Pushrods and pullbars that move substantially and lift arms that are allowed to move are components that will help create more bite off the corners in dry and slick conditions.
Dirt car steering systems must be designed to work in both left- and right-turn attitudes. Effects such as Ackermann could be more beneficial on dirt than on asphalt, but again, only to a certain degree. The Ackermann must be developed in the design of the tie rods' angles from a top view and not by creating differences in steering arm length.
To control rear steer and provide more forward bite, some dirt teams opt for the spear rod
If you were to run different-length steering arms to create Ackermann, then turning one way would produce Ackermann and turning the other way would produce reverse Ackermann.
Alignment issues, such as rear end and driveshaft alignment, present just as serious a drawback for a dirt car as for an asphalt car. There is no reason to misalign the rear end. In tests we have participated in, we have run the same lap times with the car "sideways," due to excess rear steer, and when running it straight ahead with no rear steer.
I believe that, just as stated for an asphalt car, the rear end's alignment does not need to be different from 90 degrees to the centerline of the chassis and/or to the right-side tire contact patches, and those patches need to be in line, even on dirt.
When having to steer to the right, as this driver is doing, the Ackermann effect should be
It is very difficult to maintain a correct driveshaft alignment on a dirt car. We should nonetheless try to start out with something that is close to ideal. The commonly accepted rule is that the angles between the driveshaft and both the pinion shaft and the transmission output shaft need to be equal and in opposite directions.
The driveshaft doesn't "know" which view these angles are resulting from, just that they are equal and opposite. If we have a top-view differential in alignment between the engine (crankshaft and transmission output shaft) and the pinion shaft, and they are parallel, then the angle created by that misalignment may be sufficient to provide needed angular differentials.
A 1 1/2-inch misalignment with a 44-inch driveshaft results in a nearly 2-degree angle at the tranny and pinion shafts. The engine should always be aligned perpendicular to the rear end and/or parallel to the centerline of the car.
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 we need to balance the car the way we would for asphalt, which means matching the desires of the front and rear suspensions.
The term balance means that each end of the car has its own moment arm length and resistance to roll, as well as other factors, and will desire to roll to its own angle in the turns. At midturn, each end will want to roll to its own degree of angle. The relationship between the desires of the two ends will determine the balance of the car.
The No. 00 car of Freddy Smith shows more rear roll versus front roll in this photo. Note
The No. 0 car of Scott Bloomquist, running the same turn and same race as the No. 00 car,
The cylinder with the large crank is a weight jack adjuster. With this unit, you can alter
Greatly unbalanced setups exhibit certain characteristics, such as an unusually high degree of wear and temperature, as well as wear on one tire versus the other tires and an unwillingness to turn the corner. The car will also have less bite off the corners, and the handling will not be consistent.
The best setup for slick tracks has a small imbalance 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.
Always have your shocks rated periodically by someone experienced with racing shocks. Reme
Research on shock influences on dirt have 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. Many top teams are experimenting with their shocks.
Dirt cars show a lot of travel as they negotiate the four turns. This extreme degree of wheel travel indicates that shocks on dirt cars get to do more of a job than those on asphalt cars. A shock cannot have much influence if it does not move.
Each corner of the car needs 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.
Turn entry on dirt is critical to how we are able to negotiate the turn, so we need to evaluate our turn-entry characteristics. Brake bias is a very important influence at this segment of the track. We may want to solve turn-entry problems with the brake bias on dirt.
Brake bias influence can easily be determined for any race car by entering the corner with medium-to-heavy braking first, and then entering with light braking to see if there is a difference in the car's attitude. If there is, try to adjust the brake bias to improve the entry condition.
Once you have made the entry better, check to see if your brake adjuster is centered. If it is too far to one side, then changes to the brake master cylinder sizes and/or the pad compounds may need to be made in order to solve the problem while maintaining a centered bias adjuster. Off-centered adjusters can be very inconsistent.
The lift arm helps control the acceleration and deceleration forces in a dirt car. The mor
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 replaces the lower trailing arm, causes the right-rear wheel
It's not that hard to weld a new set of bungs to a dirt Late Model car. This way, the arm
Dirt cars have been modified over the years to a more wedged shape that directs oncoming a
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 and downforce. The extra lip, or "Gurney strip" as it is cal
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.