We’ve covered the entry and mid-turn, now it’s time to see where problems can arise at the exit of the corner. Keep in mind that some handling problems have multiple sources.
Once again we’ll remind you that before you undertake this analysis, you need to make sure your team has already completed the tasks of proper alignment of the rear end, checked and set the correct toe in the front wheels, checked and eliminated bump steer and checked and reduced the Ackermann to a minimum.
We’ll also assume that your team has evaluated their front geometry and re-designed it as necessary for a more efficient front end dynamic. If not, please go back and read our numerous articles on those subjects. If so, and any one of these were out of whack, then maybe those were some of the problem. If everything checked out, then let’s continue.
Corner Exit Performance
If your car is good on entry, good through the middle, but loose or tight off the corner, then there are a few things that could be the problem. Let’s see what could be happening to hurt the car on exit.
Past mid-turn, we are beginning to accelerate. With that we have weight transfer from the front to the rear and naturally the front tires will lose grip while the rear tires will gain grip.
At the same time, as the car accelerates, the rear tires must provide sufficient grip to keep them from spinning from the torque of the engine pushing the car forward. So, some of the added grip we got from the load transfer is used up by the acceleration forces trying to spin the tires. This trade-off is not always net zero.
Much of the grip loss from acceleration happens on the initial application of power. There are a few tricks we can utilize where we can gain rear grip on initial acceleration. One way is to add compression rate to the LR shock. That way, when the car squats on initial acceleration, the load will increase on the LR as well as the RF tires and add to the cross weight percent. The increase in cross weight will momentarily tighten the car while the shock is in motion, but goes away quickly when the rear of the car settles in.
A more prolonged approach would be to initiate rear steer to the left. We do that by adding a pull bar third link, for those systems that are setup for that, and stagger the height of the trailing arms so that the left arm is lower than the right arm. When the rear end rotates as the third link is pulled out, the left wheel goes back farther than the right wheel causing rear steer to the left to tighten the car up off the corner.
If you have done all you can to provide extra rear grip on acceleration and you are still loose off, then the driver must modulate the throttle until he can go full throttle. It is easy to just stomp the throttle, but as the driver gains experience, they will learn how to modulate to keep from losing momentum off the corners.
For cars that are tight off the corners, there are several common causes. One is that the LF shock might have too much rebound setting for the spring, and/or bump you are using. In bump setups, the stiffer RR spring will resist the motion that would affect loading on the LF tire, but for more conventional setups, a stiff LF shock in rebound can seriously affect loading.
Many teams will try to run similar shocks, or stiff sway bars, to mimic the bump setups. Doing this causes the problems we have with being tight off the corner. Both the stiff rebound LF shock and a large sway bar will take load off the LF tire when we accelerate with the conventional setups. Remember, there is nothing wrong with chassis roll. Trying to eliminate it will ruin your setup.
Setups have been changing over the past five years for both dirt and asphalt race cars. With those changes come new problems, mostly created when we changed things around.
A big part of the attraction to racing is the development of the art of setup. And believe me it is an art. Some catch on easily and for some it takes more time. The better we understand what is happening to our car through the three turn segments, the quicker we can find a solution to any problems we might have.
Remember to solve all of your alignment and geometry problems first before you get into working with the setup. Problems with any of those items could be most of your problem and if left unsolved will always haunt you.
Design Engineering Inc DEI
DMI / Bulldog Rear Ends
DRP Performance Products
Integra Shocks and Springs
Longacre Racing Products
Landrum Performance Springs
Performance Friction Brakes