Have a rough season last year? Take advantage of the off-season to refine your chassis setup. Here are the top 10 most important areas of concern facing teams in dirt track racing.
Preparing your dirt car for the upcoming season should involve some processes and knowledge of technology that have been developed over the past 10 years. The approach we suggest has resulted in a lot of success and has made racing a lot more enjoyable for a lot of dirt teams.
Let's review the most important aspects of chassis setup we've presented over the last few years. Racing knowledge isn't usually shared among race teams, and for good reason. Information shared can be used against us. That's why we at Circle Track keep our eyes and ears open as we talk to racers across the country. Here are the top 10 topics for setting up a dirt car.
1. Front End Geometry For any race car with a double A-arm front suspension, we always start with an analysis of front-end geometry. If the moment center (roll center) design on your car is not right, the whole car will suffer, no matter what setup you have in it. This we have established as fact.
The primary complaint coming from dirt drivers is that their car does not turn well. The number-one reason for that is usually because the front geometry is incorrectly designed. Just improving that aspect of the car's overall design can make a huge difference in performance.
The mono-ball joint is adjustable...
The mono-ball joint is adjustable for height so you can change the height of the center of rotation and the arm angle. This helps when you need to redesign your moment-center location.
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, they are being beaten by those who have. The MC can start out left of centerline and move, after dive and roll, to around centerline or somewhat left of centerline. If you don't know where your MC is located, then you don't know the most important thing about your car.
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 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. But 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.
Pushrods and pull bars that move substantially and lift arms that are allowed to move more freely are all different ways to create more bite off the corners in dry and slick conditions. We've seen conditions where no matter what we tried, there were no improvements in lap times. The track would just give so much traction, period, and no more.
The angle of the control arms...
The angle of the control arms determines the location of the front moment center. On this dirt modified, there are two holes on each mounting tab to allow some degree of change to the upper control arm angles. The left-side arms are in the bottom holes and the right-side back link is in the top hole. This locates the MC just to the left of centerline.
It then 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 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, 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.