Dirt cars of every form are...
Dirt cars of every form are now using the left front tire more and more. The use of proper front moment center design combined with a more balanced setup keeps the four tires on the track for maximum traction.
"How dare an admitted asphalt guy tell us dirt racers how to setup our cars? Just where does he think he is coming from?" you could ask. I'm sure more than a few dirt racers have said that or a similar expression from time to time. And it's my fault that they might feel that way. I have never fully explained why or told the progression that led me to think the way I think and what my experience working with dirt teams has been. It is spotty at best, but there was a progression, so let me explain.
It was around 1996 that I met a guy named Dewayne Ragland who then worked for Bilstein shocks. He had gotten to know most of the important players in Dirt Late Model racing and was kind enough to show me around the Midwest and introduce me to people, including C.J. Rayburn. I had these crazy ideas about roll/moment center design and setup balance that I thought might as well be applied to dirt cars just like I had applied them to asphalt cars with great success.
I was a complete dummy about any aspect of dirt racing at the time, a condition that I have since found could be a plus when trying to discover something new. I didn't have the restrictions of following in the footsteps of those before me because I didn't know anything about the technology that came before me.
The First Clue
You can substitute a mono-ball...
You can substitute a mono-ball upper or lower ball joint so that you can adjust the height of the ball joints. This changes the angles of the control arms and the location and movement of the moment center. The location of the moment center dictates the efficiency of the front end.
I got a call in mid-1997 from Dewayne and he told me the team he was working with had won a race with a balanced setup. I was pleased and asked what the setup was. "We ran a 400-pound spring on all four corners," he told me. "What?" was my reply. You can't run 400-pound springs on the back of any race car. I didn't then know about the swing arm design on the Rayburn cars and so it was like running 400s up front and 200s in the rear on a four bar car. That made much more sense.
Then in late 1997, Dewayne called me and said he had this dirt guy on the phone and he wanted me to talk to him about some problems he was having. I refused to talk to him because as I told Dewayne, "I don't know squat about dirt cars." He insisted and after a long discussion where I finally agreed, he said, "I've got Billy Moyer here with me." Again I said, no f'ing way, and after another round of arguing he put Billy on the phone.
He told me his car had been very inconsistent from race to race and even in the same event. I asked some basic questions about the car, but remember I was clueless. I asked which side the J-bar was mounted on and of course he said the left side, just like everyone else-dummy. I had found with Asphalt Late Models that when the bar was on the left side of the chassis, the car was inconsistent and I said he might try running it on the other side. How stupid was that?
The angle and length of the...
The angle and length of the control arms determines the location of the front moment center. On our new Dirt Late Model, we see a long left upper control arm. This helps to reduce the upper arm angle and also helps us introduce more positive left tire camber.
Well, the next race was the finale for the '97 season of the Hav-A-Tampa Dirt Late Model Series, the Dixie Shootout, where Billy could clinch the series championship. The stakes were high. I decided to drive up from my home in Ormond Beach, Florida, to see what happened. I was there when the team took the car off the trailer and sure enough, the J-bar was on the right side. This was going to be interesting.
The short version is this: Billy set fast time in qualifying, won the dash for cash, won his heat race, and won the feature-and of course the series championship. I'm not going to sit here and say moving the bar did it, but it sure didn't hurt either. That event told me that maybe there was room for discovery in dirt racing.
The Second Clue
Then in March 1998 Dewayne and I put together a test at Eldora to try running balanced setups. At the test was Kevin Weaver driving our four bar test car and Billy Moyer running his own setups in a Rayburn car. On Kevin's car we ran a pair of 375s on the front and 175s on the rear. All day we were consistently 0.5 second, or more, faster than Moyer who was running the standard stiffer right front and softer right rear springs.
Back then Eldora had a high banked top groove of about 19 degrees and held moisture well. These were ideal conditions to run a setup more like the asphalt setups I was used to. And it worked. We shared the info with Billy and Dewayne helped him set up the Rayburn so that it would be much like Weaver's car for The Dream at Eldora that June. I think we had 375s up front and 350s in the rear. Billy won the race and the $100,000. He also came back and won the World 100 that year with Kevin finishing Second, lapping the entire field up to fourth place.
Most "four link" rear suspensions...
Most "four link" rear suspensions have adjustment of the control links using a series of holes like the new CT Mastersbilt car. We will adjust our car so that we can utilize the correct amount of rear steer depending on the conditions we will be racing. Note the high angles (the car is resting on a stand) of the links. This causes the axle on this side to roll forward and down loading the left rear tire under acceleration.
By that time, we had Scott Bloomquist, Shannon Babb, Donny O'neal, and a few others on the setup. Bloomer set fast time the first round (out of 247 cars) and was disallowed when his car weighed too light. He went back out the second round and set fast time again. He would have done well in the race but a right rear tire separated early on dropping him out.
Are you starting to get the picture here? We were having a lot of success with a process and methods that were all-new and winning is the best measure I know of to gauge how well your ideas fit, no matter which type of race car. There was a measure of validation in the way things were going.
The Third Clue
Fast forward to 2007 and a dirt test we ran at Magnolia Speedway in Mississippi with Dewayne and Jay Dickens. In that test we changed everything you could change on a Dirt Late Model car and the very last thing was to run the J-bar to the right side of the chassis. The track had medium bite, not too dry slick and not at all tacky or black.
This car is equipped with...
This car is equipped with sliding clamps mounted on square tubing. Adjustments to the link angles and J-bar heights can be made quickly and infinitely with this design. When changes are made, the rear axle must be repositioned for proper squaring.
The car laid down on the right side much like an asphalt car and the right rear tire was biting so hard that it looked like a drag slick with wrinkles in the sidewall. The lap times were no slower or quicker than any other laps we had run during the entire test, but the car was more consistent and easier to drive according to the driver (read the full article in the May '07 Circle Track).
It has long been a theory of mine that you don't need to have the fastest car to win on dirt. Many times the winner is the one who makes the fewest mistakes. A car that is hard to drive causes more mistakes and loses more time during those missteps. They don't call Billy Moyer "Mr. Smooth" for nothing and he continues to win a large percentage of the races he runs out of shear consistency.
Today, we see teams and car builders designing their moment centers more carefully and running setups where the left front tire is mostly in contact with the track surface.
In other words, the car is set up with a more balanced dynamic. What we get is not only speed, but consistency and the top teams know that is the way to Victory Lane. Here are ten things you can do this season to be more consistent and give yourself a better chance at winning.
1. Front End Geometry
The mounting of weight including...
The mounting of weight including the battery should be well thought out to gain maximum benefit for load distribution. There are times we need our weight high and to the right for dry slick track surfaces and low and left for tacky conditions.
For any race car with a double A-arm front suspension, we always start with an analysis of the frontend geometry. If the moment center (roll center) design on your car is not right, then the whole car will suffer, no matter what setup you have in it. This we have established as a fact.
The dirt car moment center design is different than that of an asphalt car. On dirt, the average g-force is much less than on asphalt because the track just 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.
2. Rear Geometry
The dirt car rear geometry layouts are varied and usually highly adjustable. Each car needs to be evaluated for where it is to be raced and then set correctly. The trailing arm angles affect the rear steer and bite and the pull bar or lift arm can redistribute load upon acceleration and deceleration.
Many teams will tell you that there is a need for rear end steer to the right at times when the car is tight and you need to get it pointed in order to exit the corner. During tight and tacky conditions, a slight amount of rear steer to the left would probably improve lap times, but only if the car turns well. The use of rear steer to the left must only occur on acceleration and not at mid-turn. This is a possibility with certain designs.
With the lift arm design,...
With the lift arm design, we can usually mount the shock in several locations farther or closer to the rearend to adjust the amount of resistance to axle rotation upon acceleration. The spring is also adjustable to cushion the forces of deceleration.
It all comes down to trying to create better driver comfort and more consistency. If a jacked up setup causes us to make more mistakes than one that places all four tires on the track, speed being equal, then opt for the more consistent setup and you will gravitate to the front.
3. Steering Geometry
Dirt car steering systems must be designed to work the same in both left and right turn attitudes. Mechanical affects 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.
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, and when running it straight ahead with no rear steer.
We are using the Integra gas...
We are using the Integra gas pressure shocks on our CT Dirt Late Model car this year. We use these on the four corners, two on the left rear at times, and also on the lift arm to control acceleration and deceleration.
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.
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.
This pull bar has a long spring...
This pull bar has a long spring that probably will not coil bind as the car accelerates. This serves to improve the bite throughout the entire acceleration zone. It is also adjustable for pre-load. These units must have a shock attached to slow down the movement on acceleration and especially turn entry.
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. 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.
7. Brake Bias
Turn entry on dirt is important and dictates how well we are able to negotiate the middle of the turn. So, we need to evaluate our turn entry characteristics related to brake bias. We may want to try to solve turn entry problems with the brake bias on dirt.
The upper control arm attachment...
The upper control arm attachment on a Dirt Late Model offers the opportunity to easily remount the arm for antidive and redesigning of the moment center. All you have to do is weld on a new set of bungs in the desired location and reattach the control arm. We have done just that with many Late Model cars.
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 conditions under heavy braking to what it is under light braking.
8. Bite Off The Corners
We could always use more bite off the corners on dirt. 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 when we are accelerating.
We should work to develop ways to create more rear traction on acceleration only so we don't ruin our mid-turn 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 pull bars with various stiffness of shocks and springs. More and slower movement is needed for slick conditions and much less movement for the tackier conditions. Another way to gain bite involves the use of a spring-loaded pushrod that allows a certain amount of forward right rear wheel movement to steer the rear end more to the left.
9. The Antis
Dirt cars have been modified...
Dirt cars have been modified over the years to a more aerodynamic wedged shape where the oncoming air is directed over the top and around the sides of the hood and not under the car. This will produce a significant amount of downforce due to creation of low pressure areas under the hood. Note the flair around the wheel wells.
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 nose dive on entry by utilizing mechanical resistance to the downward motion of the suspension.
Antisquat results from the pull bar trying to straighten out, or become more horizontal as the car accelerates and the rear end desires to rotate. The more pull bar 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 front end and/or rear of the lift arm can alter the loads among the two rear tires upon acceleration.
10. Aero Package
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 wheel wells are shaped to route air out and away from the front tires creating downforce.
The degree that you need to get involved with 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 front tires that we can get and aero generated load is not weight we have to accelerate.
The ideas we have presented and the methods we preach have a basis. I would never promote technology that I haven't seen work. I would rather not say anything rather than mislead. No one has to buy into any of what is printed here, but you do need to think out your particular setup and how you attack your racetrack.
To be more successful, it helps when you get your car set up correctly for the basics of geometry, alignment and balance. Develop a proper approach to the setups for the tracks that you intend to race at and be prepared and willing to make changes to your setup when the track conditions change. That ideology will never change.