If this looks familiar, then...
If this looks familiar, then we just might be able to help. A car that will not hug the bottom and needs excess steering input has a problem. Your job is to find the problem(s) and fix them. See if any of these tips are familiar.
The approach to setup is a mental process first and a mechanical process after that. We need to decide what our goals are in the very beginning, and the information presented here will help you formulate those goals. We need to step back and look at the big picture every once in a while. That includes where we stood with our competition during the first half of the season and what our experience level is at this point in time (our realistic expectations are directly tied to that). Also, what is our level of readiness, and finally, do we have the right tools and equipment to get the job done?
Over the past year and certainly over the past five years, we have outlined the various setup items that are most important and offered explanations and methods that will help you cope with these. Here are ten top areas of setup that can affect your handling.
1. Front Geometry - The front moment center location plays a huge role in how the front end wants to work. The MC should always be somewhere close to the centerline that is midway between the tire contact patches. The farther left the MC is located, the more efficient the front end will be and will want to roll.
Do not be afraid to attack...
Do not be afraid to attack your front end geometry and make changes where necessary. Hey, it's your car and your destiny. If you want to run up front, do what front runners do, make the changes that will help the car perform.
The farther to the right of the centerline, the stiffer the front will be and the less it will want to roll. Generally speaking, low-banked tracks require a location more to the left, and higher-banked tracks are best set up with an MC more to the right of centerline.
Camber settings dictate how large the contact patch is. The RF and LF wheels will always experience changes in camber as the car enters and rolls into the turns. If the front geometry is not designed correctly, then as the car dives and rolls, the cambers relative to the racing surface will not be correct to provide the largest possible contact patch.
With the advent of the BBSS asphalt setups, both front wheels experience a great deal of camber change as the chassis dives three inches or more in the turns with an accompanying reduction in chassis roll. Because of restraints in design and the need for geometry controls for Moment Center placement, we have to live with those properties. Initial camber settings must be revised when changing from conventional to BBSS setups. The LF static camber must be increased quite a bit and the RF static camber must be decreased.
The lower control arm angles...
The lower control arm angles control the amount of movement of the moment center from static to dynamic location. Tune your control arm angles to position the MC and keep it from moving too far as the car dives and rolls.
2. Ackermann - In the front end geometry there is a condition called Ackermann. This is an effect that increases the amount of toe-out in our race cars when we turn the steering wheel.
The opposite of Ackermann is called Reverse-Ackermann. That is an effect that causes an increase or decrease in the amount of toe-out as we steer, and can actually cause the front tires to end up with toe-in if Reverse is severe. It is possible to have Ackermann in our steering system when we steer left and Reverse Ackermann when we steer to the right. You do not need Ackermann in your race car, period.
3. Rear Geometry - A car that is loose in the middle and/or loose on entry to the corner can have several problems. If the car is severely loose, and nothing seems to help, it is almost always rear end alignment. If the rear end is pointed to the right of the centerline of the car, it will want to swing to the right as the car is steered left.
If the rear end is not aligned properly, the car may be either tight or loose in all three phases of the turns. One of the very first tasks in setting up a race car is to make sure all of the alignment issues have been corrected. The rear end should be at right angles to the chassis centerline and the right side tire contact patches should be inline.
Ackermann is one setting that...
Ackermann is one setting that can ruin an otherwise great setup. In this day and age, we no longer need Ackermann to help turn the car. Reduce your Ackermann to near zero.
Every race car needs a certain amount of tire stagger. The rear tire sizes must be different in order to compensate for the turn radius so that both rear wheel RPM will be equal. Excess stagger should never be used as a crutch to help make the car turn if it is tight.
4. Balance and Crossweight - A loose or tight car can also be caused by a tight or loose setup. Either of these two can be caused by an unbalanced setup, or by running the wrong amount of crossweight percentage. Tire temperatures can tell a lot about the setup and where we need to look to fix the setup balance problem.
In the case of an unbalanced setup causing a tight condition, the rear of the car wants to roll more so than the front. There are several things we can do to help balance the car. We can raise the panhard bar to raise the rear moment center which will cause the rear suspension to want to roll less. We can reduce the rear spring split if we are using a softer right rear spring by stiffening the RR spring and/or reduce the LR spring rate.
To reduce rear steer, find...
To reduce rear steer, find the trailing arm angles that will serve to locate the rear end with chassis movement so that there is very little rear steer. Even with the dirt teams, rear steer is being re-evaluated.
At the front end, we can do a few things to cause the front to roll more to try to match the rear roll angle. If we have a much stiffer RF spring, we can soften the RF spring, stiffen the LF spring or run a stiffer LF spring than the RF spring on flatter tracks. The stiff LF spring setup does not work well on tracks banked over 10 degrees. Changing to a smaller sway bar will also increase the front roll angle. With the BBSS setups, reduced roll angle is the overall goal, but teams have been changing to smaller bars of under 1 1/2 inches recently.
With the BBSS setups, the front may want to out roll the rear, causing excess load to be put on the right rear tire through the turns. This happens when the crew knows there needs to be a spring split in the rear by installing a stiffer RR spring than the LR spring, but goes overboard and uses much too stiff a RR spring. When the LR tire is the coolest on the car, the rear spring split may be too much.
5. Tight/Loose Syndrome - A car can appear to be loose when in fact it is tight. This condition is very hard to detect from a driver's perspective. The feel is that the car is loose right at mid-turn and off the corner. What sometimes happens is that the car is tight and the driver turns the steering wheel far enough to get the car to turn.
Balance in chassis setup involves...
Balance in chassis setup involves the relationship of the front suspension to the rear suspension in a dynamic sense. These two systems influence each other because they are attached by the chassis. So, we need to make sure they are happy with each other in their actions. Getting along applies to our setups too.
Because the front tires generate more traction with a greater angle of attack, the driver is actually putting more traction into the front end. The once tight condition now switches to loose as the front gains grip from excess steering angle. This happens very quickly and the rear end snaps loose as the throttle is applied. All the driver knows is that the car is loose. To correct this, we have to fix the tight condition to cure the loose condition. This malady is more common than most racers know.
6. Shocks - For a car to be fast, the driver must have a good feel for what the car is doing. A soft ride that feels sloppy does nothing to give a driver confidence in knowing what the car will do next.
Many racers think that increased compression in the shocks should help this problem, but too often that has an opposite effect. The car may indeed need more compression in the shocks, but the rebound should always be higher than the compression to control excess body sway and roll. In most cases, just increasing the rebound resistance will solve the problem.
Again, with the Big Bar and Soft Spring setups, excess movement of the suspension can be a problem. Higher rebound rates are essential for controlling suspension movement. Many of the tech support persons who work for short-track shock companies have worked out shock valving solutions for those who want to experiment with the BBSS setups.
For the teams who run swing...
For the teams who run swing arm rear suspensions where the shock/spring is mounted on the trailing arm, be aware of the motion ratio. Depending on the mounting point location, the car can feel around 50 percent of the installed spring rate or less. These cars must be sprung double the spring rates as those used on cars with the coilovers mounted to a clamp or birdcage on the rear axletubes.
For dirt cars where a lot of vertical movement is desirable to get more load transfer on dry slick racetracks, reduced compression and rebound may be helpful, and a lot of movement should be expected. Of course, this depends on the track conditions. The tighter the track, meaning the more grip, the more we need to control the suspension movement by stiffening the shock rates, especially the rebound.
7. Brakes - Make sure your brake bias is tuned correctly. If too much of the bias is on the rear brakes, the car will be loose under heavier braking. If you lightly brake into the corner and the problem diminishes, then brake bias is the culprit. It helps to install brake bias gauges and then adjust the amount of pressure front to rear. Usually a 60- to 65-percent front and 35- to 40-percent rear bias works for most asphalt tracks where a greater amount of rear brake works to help a dirt car on entry.
8. Anti-Pro Dive - If the car is diving excessively under heavy braking, the RF wheel loses camber quickly and that tire will loose traction. Although the camber change is quick and the wheel returns to normal camber settings a short time later, once the push starts, it is hard to stop it without slowing down. Anti-dive effect can help the situation.
Adjustable shocks can be a...
Adjustable shocks can be a major tuning tool. The graph shown shows the rebound sweep, or the range of resistance available in this build. This is one of the Ohlins shocks we are using on our asphalt project Late Model car. We have a lot of choices with these shocks.
We can also use Pro-Dive to hasten the movement of the left front corner on turn entry. Most teams that do this also are running the BBSS setups and desire to drop the front end as low and as quickly as possible on turn entry. Using Ant-Dive on the RF and Pro-Dive on the LF helps square the front end to the racetrack and along with a softer spring setup provides an enhanced aero effect.
9. Driving Style and Track Transitions - The shape of the racetrack can affect how the car is balanced when exiting the turns. If the transition is abrupt and the top of the track drops to match the inside edge elevation, then the RF will follow the drop-off and unload the LR wheel. Shock rebound rates need to be reduced to allow the LR tire to stay in contact with the racing surface.
Driving style can have an effect on handling too. The best driving line might be in a different place than what feels fast to the driver. The stop watch and passing performance depend on driving the correct line, not what feels fast to the driver.
Some teams use Pro-dive on...
Some teams use Pro-dive on the left front upper arm to enhance dive on entry under braking. Instead of causing a resistance to dive from the braking forces, pro-dive promotes dive and causes the left front to quickly lower and provides a flat and low profile of the front nose of the car.
A driver that dives into the corner low and then pinches the middle does the tires no good and will end up losing a lot of ground to drivers who are more disciplined and drive in wider to increase the radius of the middle of the turn. Carefully watch the line your driver is using and think out if that line is the best one for helping to maintain momentum in the turns.
10. The 99 Percent Rule - If we race long enough, we will eventually stumble on a setup that wins and may provide us with that coveted championship. But racers are racers and we all like to experiment. So, we lose track of the setup that might have won the first race of the year. One very important aspect of race car setup is the 99-percent rule. When you are the fastest car on the track and you are winning races, any change you make has a 99-percent chance of slowing the car down.
Make sure you keep good notes.Refer to those notes before, during and after making any changes. Reference how fast the car is on short runs and on longer runs. Two setups might be equal on shorter runs, but one may be more consistent and that is the one you need to stay with. Most teams are only after the fastest lap setup, but will get beat time and time again by cars that are more consistent and faster at the end of the race.
We hope these tips will cause you to rethink certain aspects of your approach to handling problems. If you are in the points lead or close to a good points position, go over some of these items and make sure everything is where it should be. Then push on to the end of the season and make every effort to run as hard as you can. This all might help you end your season on a high note.