It's been three years since we discussed the subject of handling fixes. In that time, a lot has changed with how racers on asphalt set up their cars. So, with some of the information we have learned over those years applied, here is a modernized version of that article. The basics remain the same, but with a few critical adjustments.
Good handling has often been thought of as a car that is neutral as it runs through the entry, middle, and exit phases of the corner. That is fine as a goal, but what we really want is both balanced and neutral. The setup that will stay consistent throughout the race is the one that wins, and balance provides that consistency.
We should divide the turn...
We should divide the turn into three phases or segments in order to analyze the handling. The middle phase is most important to overall track performance. Entry and exit performance helps us pass cars on the racetrack.
Here is a recent quote from a reader who has found that perfect balance. "In the 50-lap Main, our fastest lap time was clocked on Lap 43. We were 0.13 faster than we qualified. The chassis was as good or better at the end than it was at the beginning."
When the car is not balanced, the neutral handling does not stay with the car for very long. An unbalanced car can be very fast, although the thrill lasts but for a short time. So testing for the fastest lap does not guarantee success. Here, we will examine the problems associated with a car that handles poorly and some logical steps to take to find the most balanced setup.
A poor handling car is defined as one that is either loose (rear has less traction than the front) or tight (front has less traction than the rear). The wine-and-cheese crowd refers to these as oversteer and understeer. Let's stay with the circle track lingo. The tight or loose condition can exist in one or more of the three phases of a turn (entry, middle, and exit). The cure must address where the car is not handling and ideally not affect those areas where the car is good.
The moment center (sometimes...
The moment center (sometimes called the roll center) location is very important in determining how efficient the front end will be. It helps the car turn and provides balance for the overall setup.
We will look at each phase of the corner and offer handling remedies based on the phase they affect. We should start with the mid-turn handling because problems that affect the car in the middle can also affect the entry and exit. If we can get the car to handle well in the middle, then we might have already solved some of the entry and exit problems, too. Usually, improved mid-turn handling offers the most gain in overall performance, and that is why we start there. We also want to make sure that adjustments to other segments later on do not affect the mid-turn handling.
Mid-turn handling problems are caused by a car that is either tight or loose. By far the most common handling malady historically is inability to turn. This can be caused by several different conditions, or a combination of those. We will need to go through a checklist to eliminate some familiar problems. The following is a list of things that can make the car not want to turn or make the car loose.
The amount of Ackermann in...
The amount of Ackermann in our rack-and-pinion steering system can be regulated by moving the rack forward or backward in the car. This adjusts the top-view angles of the tie rods to change the amount of spread that occurs between the ends of the steering arms as we steer the car. This is a great way to adjust Ackermann for dirt cars, where steering is in both directions.
The front moment center (MC) location plays a huge role in how the front end wants to work. The MC should always be somewhere close to the centerline (i.e., 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. The farther to the right of the centerline, the less the front end will want to roll. Low-banked tracks require a location more to the left and higher banked tracks are best set up with a MC more to the right of centerline.
The center of gravity (CG) height influences where the MC should be located. Cars with a lower CG should have a MC that ends up farther to the left side of the scale than would cars with a higher CG.
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 a decrease in the amount of toe-out as we steer and can actually cause the front tires to end up with toe-in if the effect 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.
We can change the amount of...
We can change the amount of Ackermann in our drag link steering system in a way similar to how we adjust the rack-and-pinion system. If we move the drag link forward in the car, we will take top-view angle out of the tie rods and reduce the amount of Ackermann in this system.
With excess Ackermann designed into our cars, on purpose or not, we can gain a lot of toe-out, which causes our front tires to work against each other. When this is severe, the front end will push and no adjustment to other setup parameters will seem to help the situation. When running balanced setups that work the left-front tire, we must eliminate most of the Ackermann.
In the common asphalt setups of today, where we use a larger sway bar and softer springs (BBSS), the presence of Ackermann effect could be more detrimental. As we use the left-front tire more and more, the negative results of Ackermann become more apparent.
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.
The primary goal of all setups...
The primary goal of all setups is to develop a balance between the two ends of the car so that they will want to do the same thing in the turns. Once we find a balance that works through the middle of the turn, we need to maintain this setup balance as we try to fix entry and exit handling problems. The Big Bar and Soft Spring setups can be very unbalanced, causing big problems.
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 with the wrong amount of crossweight. 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 roll 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 (RR) spring by stiffening the RR spring and/or reducing the LR spring rate.
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 increases the front roll angle, but not very much. We mostly use the sway bar to tune for traction off the corners. With the BBSS setups, reduced roll angle is the goal, so using a smaller sway bar is out of the question.
There is a correct amount...
There is a correct amount of crossweight for every combination of setup and weight distribution for your car. If your car needed 51 percent and you run 52 or 53 percent, the car will be tight. There is no need to change springs to try to loosen the car. You need to lower the crossweight by taking cross or wedge out of the car. The correct procedure is to balance the car with some amount of crossweight distribution and then read the left-side tires. If the LF and LR do not have matching tire temperatures, start changing spring rates, moment centers, and so on to balance the car. As the balance is corrected, the crossweight must change with the other changes to maintain the handling balance.
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 and installs a stiffer RR spring than the LR spring, but goes overboard and uses a RR spring that is much too stiff. When the LR tire is the coolest on the car, the rear spring split may be too much.
If all else were correct, such as alignment, Ackermann, setup balance, and so on, and the car was still tight or loose, then the crossweight percentage is probably wrong for the weight distribution in the car. Reduce the crossweight in a tight car and increase the crossweight percentage in a loose car.
A car can appear to be loose even though it is tight. This condition is very hard to detect from a driver's perspective. The car is loose right at mid-turn and off the corner. Sometimes the car is tight and the driver turns the steering wheel far enough to get the car to turn.
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.
The pullbar is just one device...
The pullbar is just one device that racers use to reduce "shocking" of the rear tires as the driver gets back into the throttle. The link is spring loaded and allowed to extend against the pressure of the spring to absorb some of the force of initial acceleration.
The entry and exit to and from the middle are affected by transitional components in the car. Transitional components include the shocks, rear roll steer, brakes, rear steer under power, camber change, rear stagger and the Anti's (dive and squat). Let's go through each item and explain how they can affect our turn entry and exit performance.
The overall rate and the layout of different shock rates on the car can greatly affect the weight distribution, and therefore the handling, in the transitional phases on the racetrack. If we are loose going into the corner, the LR shock may be too stiff in rebound or the RF shock may be too soft in compression, which transfers load off the LR tire on initial entry under hard braking. To fix this, reduce the rebound rate in the LR shock and/or stiffen the compression rate on the right-front shock.
If the rear end is positioned...
If the rear end is positioned so that it is aimed to the right of the centerline of the car, the rear tires will continually want to roll outside the front tires. This is obviously going to make the car very loose in all three of the turn phases. It is very important to align the rear end to point straight ahead and also to line up the right-side tire contact patches.
Try to install shock rates to complement the car's setup. Most top shock technicians will be able to help you select the proper shock rates to go along with your particular setup related to your type of racetrack.
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 60-65 percent front and 35-40 percent rear bias works for most tracks.
Some rear suspension systems can be adjusted for rear steer. If the geometry is such that the rear end is made to steer on turn entry so that the RR wheel is farther to the rear than the LR wheel, we have rear steer to the right. This can make the car very loose and we need to adjust the suspension components so that it will not steer in this manner.
There is a design for a three-link...
There is a design for a three-link rear end that utilizes the motion of a pullbar. The LR spring is mounted in front of the rear end and the RR spring is mounted behind the rear end. When the car accelerates and the rear end rotates as the pullbar extends, the LR spring compresses and the RR spring decompresses. This adds load to the LR wheel and takes load off the RR wheel. This usually causes the rear tires to be more equally loaded, and the car will have more traction to help provide better bite off the corners.
If the car is diving excessively under heavy braking, the RF wheel will lose camber quickly and its tire will loose traction. Antidive effect can help the situation. 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.
We can also use prodive to hasten the movement of the left-front corner on turn entry. Most teams that do this also run the BBSS setups and desire to drop the front end as low as possible and as quickly as possible on turn entry. Using antidive on the RF and prodive on the LF helps square the front end to the racetrack and, along with a softer spring setup, provides an enhanced aero effect.
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 RF camber relative to the racing surface will change and the tire will lose grip. In testing conventional setups over a five-year period, it was discovered that most tires want no change in camber relative to the racetrack surface as the car dives and rolls.
The front mounting bracket...
The front mounting bracket on a three-link rear suspension is adjustable to allow the team to change the angle of the trailing arm. The driver can feel small changes to the height of the front of the right trailing arm.
With the advent of the BBSS setups, both front wheels experience a great deal of camber change as the chassis dives 3 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.
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 the rpm in both rear wheels will be equal. Excess stagger should never be used as a crutch to help make the car turn if it is tight. Doing this will probably make the car loose off the turns while under power.
A pushrod trailing arm is...
A pushrod trailing arm is designed to compress when the car is accelerating. This shortens the link and allows the rear end to steer to the left, which tightens the car considerably. Most teams that find this useful find it necessary to tighten the preload on the rubber biscuit to limit the amount of movement. Small amounts of rear steer go a long way toward tightening the car off the corner.
Some teams refuse to run sufficient stagger to match the radius and banking of the racetrack. I have talked to racers who run on tracks that require 1.75 to 2.00 inches of stagger. They report running about 0.75 inch and complain that the car is tight off the corners. It's no wonder.
Stagger affects handling in each phase of the corner if the car has a locked rear differential. With a Detroit Locker, or similar differential, the axles will unlock going in and through the middle and lock up on exit while under power. So, with the Detroit Locker rear end, stagger should match the radius of the turn where the car is starting to accelerate and the rear end is locked.
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 adjusted to allow the LR tire to stay in contact with the racing surface.
A useful design tool is antidive...
A useful design tool is antidive and prodive. Antidive keeps the front suspension from moving too quickly and too far. Prodive causes the front suspension to move more quickly. These two only work while we are braking, and that is exactly when we need them to work. Antidive is accomplished by angling the control arms from a side view so that as the spindle tries to rotate under heavy braking, the motion of the ball joints is in the reverse direction and resists dive. Prodive works in an opposite manner.
If the LR shock has too much rebound, then that tire will lose a lot of load and not be able to provide traction. The RR tire will be the only one trying to accelerate the car, and it might spin. Decrease the amount of rebound in the LR shock and/or soften the rebound in the RF shock to help this situation.
When attempting to tune your car's handling balance at the racetrack, always start with the middle phase of the turns. Run the car at a moderate speed through the middle well below race speed and note how far the steering wheel is turned. Speed up and do a few hot laps, and again note the position of the steering wheel.
If the wheel is turned farther at speed, the car is tight. If it is turned less, it is loose. If you have to steer to the right at mid-turn, bring the car back in. That simple test has helped many teams quickly determine the status of their setups so they will quickly know which direction to go when tuning the mid-turn handling.
Next, tune the entry balance and then tune the exit balance. When all three phases are balanced, work on driver finesse and practice passing maneuvers running high and low off the corners. With the car set up correctly, it is just a matter of experience and a little racing luck that brings that first win. In the next issue of CT, we will delve into the setup problems for a dirt car.
The rear stagger should be matched to the racetrack and not used to correct handling problems. A particular car at each racetrack will require a certain amount of rear stagger. The track radius used to determine stagger matters the most where the car will be accelerating. On some tracks, with cars using Detroit Locker rear differentials, the accelerating portion radius will be larger than the mid-turn radius. Therefore, less stagger should be used so that both rear wheels are turning the same rpm off the corner to avoid wheelspin.