If the right trailing arm...
If the right trailing arm is mounted higher than the left-side arm, then as the rear end rotates, the LR tire will move to the rear more so than the RR tire, resulting in rear steer to the left.
Asphalt cars merely need to maintain a straight-ahead attitude when cornering. Dirt cars must steer the rear end to the right on dry-slick tracks to develop a more sideways attitude that will point the car in the right direction to be better able to get off the corners. In past years, the drivers on dry-slick tracks needed to throw the car sideways in the turns and, in the process, break the rear tires loose in order to point the car.
When it was time to get back into the throttle, the tires had already lost traction and just spun, producing little forward bite. With the advent of radical rear steer geometry, the cars now roll over, the rear end steers to the right to point the car, and the rear tires maintain grip with the track surface and are ready to provide forward bite when the driver gets back into the throttle.
A fairly new concept for added bite on asphalt involves a geometric design that produces rear steer upon application of power. We can utilize a certain type of rear suspension to create rear steer only under acceleration. In the three-link rear suspension system, if we use a pull bar, lift bar, or other similar device that allows the rear end to rotate under acceleration, we can steer the rear end to the left while the car is accelerating.
As the rear end rotates under power with the pinion moving upward, the whole rear end will move rearward. If the lower control arms are mounted at different distances from the axle, then one side of the rear end will move farther than the other. If the left-side trailing arm is mounted lower than the right-side trailing arm, then the LR wheel will move rearward more so than the RR wheel, resulting in rear steer to the left, which will tighten a car off the corners.
Data acquisition not only...
Data acquisition not only tells us exactly how our drivers use the throttle, but also how the traction control devices are working. In this example, we see a graph from a dirt Late Model car at a test at Eldora. We can see that as the throttle is applied (purple top line), the pull bar (red line) begins to extend.
Initially, the driver applies about 30 percent throttle and then gradually increases throttle all the way down the straightaway to 100 percent near the end. The engine rpm (black line) never spikes, indicating that the rear tires never break loose. The pull bar controls the engine torque, and the driver uses good throttle control.
It is not widely known, but some top dirt racers have adjusted their cars' engines to produce less horsepower when slick track conditions would not allow great amounts of torque and horsepower to be put to full use. Using smaller carburetors, adding restrictor plates, unhooking the secondary butterflies, or using electronic traction control that changes the timing or breaks down the ignition on one or more cylinders are all ways teams reduce engine output.
We have seen teams change to a smaller engine when they knew they were going to a traditionally dry-slick track. Again, anything we can do to help the rear tires maintain grip at all times will give us a better chance to apply the power available to accelerate the car
When all available and useable methods of promoting traction control have been utilized, it may still be difficult to apply power without losing rear traction. In that case, it comes down to the drivers using their skills to help prevent loss of rear traction when coming off the corners.
Many top drivers have perfected the art of throttle control to help maintain traction. This means that if the driver knows he or she cannot apply full throttle without the rear tires spinning, the driver will work to apply just enough power to accelerate without breaking the tires loose. This method applies to both dirt and asphalt racing and is much harder to master than most might think. Truth be known, many of our most successful drivers overcame less than perfect setups using this technique.
There is a story about the late and great Dale Earnhardt Sr. at a test at the Richmond racetrack years ago. Among the many teams there, one team in particular was having unknown problems and going slow. The struggling team's owner knew Dale and asked him to take the car out and see if he could determine the problem.The car had a data recording system, and one of the functions that the system showed was throttle travel.
Dale promptly went out and ran a full second quicker than the usual driver with the same setup. Later on, a close review of the throttle graph showed that Dale was rolling on and off the throttle, and the graph looked much like a roller coaster. The other driver's throttle graph looked like a group of large square buildings-straight up and down, or quickly on and off the throttle. He was off the throttle much too quickly going into the corner, and was waiting too long to get back into the throttle. He delayed using the throttle off the corners to avoid spinning the tires as he accelerated. This example best defines driver-induced traction control. It can be a major factor in reducing lap times. Improving traction off the corners is mostly about three things:
1. Balancing the setup and geometry so that the rear tires are always gripping the racetrack, ensuring that the car is not tight (leading to the "tight/loose" syndrome).
2. Applying traction methods to enhance weight distribution and overall mechanical grip off the corners as needed.
3. Learning to recognize the amount of traction that is available and helping the driver know when he or she has done all that is mechanically possible to enhance forward bite. At that point, it is up to the driver to modulate the throttle correctly to further maintain grip between the tires and the track surface.
Your driver may never be able to mash the gas and go, but as Scott Bloomquist once said, "My goal is to go wide open all of the way around the racetrack. I know that's not possible, but the closer I can get to doing that, the better I like it." Like Scott, learn to develop a legal traction control package that maximizes performance through enhanced traction off the corners. Your lap times will get better, and the car will be more competitive while you try to get by lappedtraffic or pass for position.