In years past, a fast race car was considered one that was neutral in handling. Neutral is definitely a goal, but we have learned more about what makes a race car capable of winning. What we really need is a car that is neutral and dynamically balanced that will stay consistent throughout the race. If you have listened to Nextel Cup or Formula 1 racing, you have heard the teams speak in terms of the balance of the setup. This is what they are talking about.
When the car is not neutral, there are both good and not-so-good ways to make it neutral. Here, we will examine the problems associated with a poor-handling race car and some logical changes to create a more-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), or what the "left-and-right" racers refer to as "oversteer" and "understeer." These conditions can occur in any of the three phases of the turns, entry, middle, or exit, or any mix of the three. The cure must address the phase where the car is not handling, while ideally, not taking away from the areas where the car is working well.
Dividing the turn into three...
Dividing the turn into three phases or segments helps us concentrate on the way the car handles in each phase.
Let's take a look at each phase of the corner and present handling solutions based on what the car is doing at each point. We will start with midturn handling because the problems that affect the car in the middle can also affect entry and exit performance.
If we can get the car to be balanced in the middle, then we might solve some of the entry and exit problems, too. Usually, improved midturn handling offers the most gain in overall track performance, and that is why we start there and then make sure that segment remains good as we make changes to improve the other two phases.
Midturn HandlingMost midturn handling problems have been related to cars that do not turn very well. With the advent of new big bar and soft spring (BBSS) setups on asphalt, that trend has reversed so that the more common problem with BBSS setups is that the car is loose in the middle.
By far the most common handling problem across the industry is a car that will not turn. This can be caused by certain individual conditions or a combination of several. We can go through a checklist to eliminate some familiar problems. The following, in order of significance, is a checklist of things that can prevent the front end from turning.
These two cars exhibit very...
These two cars exhibit very different attitudes, which leads us to think they have entirely different setups in their cars.
1. Front Moment Center Location As has been stated many times before, the front moment center location plays a huge role in how efficient the front end will be. The MC should always be located in close proximity to the centerline that is established as the midway point between the tire contact patches.
The farther left the MC is located, the more efficient the front end will be, and the car will feel like it has softer springs. The farther to the right of the centerline, the less efficient the front end will be, feeling somewhat hard-just like running very stiff springs. Cars running on lower-banked tracks require a location more to the left, and cars running on higher-banked tracks are best designed with an MC more to the right of centerline.
The center-of-gravity (CG) height also influences where the MC should be located. Cars with a lower CG can have an MC design that is located farther to the left than that of cars with a higher CG.
2. Excess Ackermann In the realm of front-end geometry, there is a condition called Ackermann. This is an effect that is part of the design of the steering system. If Ackermann effect is present, there is an increase in the amount of toe-out when we turn the steering wheel. The Ackermann effect can happen only when the wheels are turned left or when turned both directions.
The moment center (what used...
The moment center (what used to be called the roll center) location is very important in determining how efficient the front end will be, and a proper design helps the car turn and provides a more balanced overall setup.
The opposite of the Ackermann effect is called reverse Ackermann. This is a designed-in effect that causes a loss in the amount of toe 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.
With Ackermann designed into our cars, whether deliberate or not, we can gain a lot of toe-out, which causes the front tires to scrub and lose traction. With excess Ackermann, the front end will push and no adjustment to other setup parameters will help the situation. We must eliminate most of the Ackermann in our steering systems. The solution is different for the two most common types of steering systems we find in circle track stock cars.
In the rack-and-pinion steering system, if we have equal-length steering arms and still have excess Ackermann, we need to reduce the top-view angle of the tie rods. We do this by moving and mounting the rack more forward. As we take the top-view angle out of the tie rods and make them more perpendicular to the centerline of the car, we reduce the amount of "spread" that occurs as we turn the steering wheel, and the outer tie-rod pivots move rearward through the arc created by the steering arms.
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 the most practical way to adjust Ackermann in a dirt Late Model due to the fact that we steer both ways on dirt. This solution eliminates Ackermann in both steering directions and does not create reverse Ackermann.
A common solution for asphalt cars, and one that is not recommended for dirt cars by virtue of them having to steer both ways, is to change the lengths of the steering arms so that each spindle turns the same number of degrees as the other. If we have Ackermann present in our car, we can lengthen the left steering arm to slow down that spindle and/or shorten the right steering arm to speed up that spindle. Again, this only works to reduce Ackermann when we steer to the left.
In a stock-designed drag-link system, we can move the drag link forward to reduce the amount of Ackermann for dirt or asphalt cars. On asphalt, the same quick fix can be used by lengthening or shortening the steering arms, as discussed earlier with the rack-and-pinion systems.
3. Rear Alignment 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 the alignment issues have been resolved. The rear end should be at right angles to the chassis centerline, and the right-side tire contact patches should be in line.
If the rear end is misaligned, with the wheels pointed left of centerline, then the car will be very tight and won't turn well. This is another condition that will override proper MC design, a balanced setup, and minimal Ackermann. If not remedied, this problem will ruin an otherwise great race car.
Some spindles have a slotted...
Some spindles have a slotted hole in the left steering arm. This allows adjustments to the length of the steering arm in order to reduce Ackermann effect.
4. An Unbalanced Setup A tight car can also be caused by a tight setup, a result of an unbalanced setup or running the wrong crossweight percentage. Tire temperatures reveal a lot about the setup and where we need to look to fix the balance problem.
If the average temperatures of the front tires are higher than the average temperatures of the rear tires, then the car is probably tight and may have too much crossweight. The car should respond to a reduction in crossweight, but this adjustment does not necessarily fix a setup that is dynamically unbalanced.
In the case of an unbalanced setup causing a tight condition, the rear of the car will tend to roll more than the front. There are several things we can do to help bring a better balance to the car. We can raise the Panhard bar to raise the rear roll center, which will cause the rear suspension to stiffen and roll less.
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.
We can reduce or eliminate the rear spring-rate split if we use a softer right-rear spring. That too will reduce the rear roll angle. If we are running on a banked track of 12 degrees or more, we can also increase the rate of the RR spring over the LR spring rate to reduce the rear roll angle.
At the front end, we can do a few things to cause the front to be softer and tend to roll more in order to try to match the desire of the rear. We can soften the RF spring and stiffen the LF spring to make them equal, or even install 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. Using 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 conventional setups.
5. Crossweight Percentage Crossweight percentage is defined in circle track racing as the sum of the RF and LR wheel weights divided by the total vehicle weight. If all else is correct, such as alignment, moment center location, dynamic balance, camber change, and so on, and the car is still not neutral, then the crossweight percentage is probably wrong for the weight distribution in the car. Reduce the percentage of crossweight for a tight car and increase the crossweight percentage for a loose car.
A balanced car is evidenced by tire temperature readings. The front and rear averages should be close to the same (add the front two tire temperatures and compare to the rear two tire temperatures), and each of the side tires should have nearly the same temperature front to rear. For example: LF + RF = LR + RR, LF = LR and RF = RR. Work to get these temperatures correct and then fine-tune the handling balance with the crossweight percentage.
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 tend to do the same thing in the turns. We need to maintain this setup balance as we try to fix entry and exit handling problems.
When the car turns well but the rear is not gripping as well as the front, the car is said to be loose. The feel of the car as well as the tire temperatures can reveal a lot about what is causing the loose condition.
A loose car usually has a RR tire temperature that is higher than that of the other three tires. That is because a loose car does not have enough traction off the corners and spins the rear tires, especially the RR tire. Here are several probable causes and solutions for a loose car.
1. Rear Alignment The very first consideration is rear alignment. If the rear end is out of alignment, with the RR wheel farther back than the LR wheel, the car will be loose at all three segments of the turns. This should have been checked in the shop long before the car rolled off the trailer.
A simple stringing of the wheels in relation to the chassis side rail will tell you if the rear-end alignment is off. When testing or in practice, do a quick adjustment-bring the RR wheel forward and go back out on the track. The condition should be better. Do a thorough alignment check when you return to the shop.
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 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.
2. High Rear Roll Center The Panhard bar, or whatever represents the rear roll center height, may be too high for the rest of the setup. If you have a J-bar setup or a Panhard bar, lower it to tighten the car.
Small changes will make a noticeable difference. If the car is way off, make changes in 1/2-inch increments. As the car approaches neutral, make 1/4-inch changes on both sides and then on only one side.
3. Stiff Rear Springs The rear springs may be too stiff, resulting in the front tending to roll more than the rear. This was not a common occurrence in years past, but it is very possible with the advent of the BBSS setups. Soften the rate of the rear springs to help eliminate a loose condition.
Soften only the RR spring in a BBSS setup. Rear spring changes have a significant effect on the handling balance, so be careful. The changes you make, if in excess, can cause the car to revert to a tight condition in a hurry.
With these changes, if you are able to set up the car so that it is neutral and balanced through the middle of the corner, then the next step in the process is to work on entry performance.
The rear trailing arms are...
The rear trailing arms are positioned so that as the right side of the chassis moves down in the turns, the right-rear wheel is moved back, causing a significant amount of rear steer to the right and making the car loose.
A car that is loose into the corner may have one or a combination of the following problems. Let's look at what makes a stock car loose on entry.
1. Rear Alignment A rear end that is out of alignment can cause a car to be very loose, especially on entry to the corner. If the rear end is aligned so that it points to the right of the centerline of the car, then the car will probably be loose into the corner as well as through the middle and off the corner. Nine times out of ten, a car that is loose into the corner has a rear alignment problem that needs to be addressed right away.
2. Improper Shock Rates The LR shock may be too stiff in rebound or the RF shock may be too soft in compression, which transfers load from the LR tire to the RR tire, and from the RF tire to the LF tire on initial entry under hard braking. To fix this, reduce the rebound in the LR shock and/or stiffen the compression in the RF shock.
3. Brake Bias Imbalance Incorrect brake bias adjustment can cause a loose-in condition. Make sure your brake bias is tuned correctly. If too much of the bias is on the rear brakes, the car will be looser under heavy braking than if you lightly brake into the corner. Install brake bias gauges and know the amount of pressure at each set of brakes. Usually, a 60 percent front and 40 percent rear bias works for most tracks.
For dirt cars, we sometimes see a bias adjustment between sets of brakes on the same "axle." Usually, this is done at the front, and the RF is made to brake less, or not at all, to prevent it from losing grip on entry. This could overwhelm the LF tire, so a change in front-to-rear brake bias is recommended along with a left-to-right bias adjustment at the front.
A useful design tool is antidive....
A useful design tool is antidive. Antidive keeps the front suspension from moving too quickly and too far. It only works while we are braking, and that is exactly when we need it to work. Antidive is accomplished by angling the control arms from a side view so that the front is higher than the rear. Slotted upper control arm mounts using slugs make setting antidive easy.
4. Rear Steer Some rear suspension systems can be adjusted for rear steer. If the adjustments are such that the rear end is made to move so that the RR wheel is farther to the rear than the LR wheel, we have rear steer to the right. This makes the car very loose and we need to adjust the suspension components, such as the trailing arm angles, so it will not steer in this way.
If the car is a dirt Late Model and the track is very dry-slick, a small amount of this type of rear steer can actually help the car keep grip with the rear tires. This is a special case, and in almost every other situation, we try not to steer the rear of the car to the right, be it dirt or asphalt.
A car that is tight on entry, once the middle phase has been sorted out, could be negatively influenced by conditions that are only caused by the motion and dynamics of braking. Braking can contribute to conditions such as excess camber change, improper load redistribution, excess dive (causing bumpsteer), or chassis compliance problems (bending of components) as well as the obvious brake bias adjustment.
1. Improper Shock Rates The shocks control the motion of the suspension during the transition phases. Corner entry is one of these phases, and as the car slows and turns left, the loads on the tires are redistributed.
If the car is tight on entry, the LR shock may be too soft in rebound or the RF shock may be too stiff in compression. Either will tend to load the RF and LR tires on initial entry under hard braking. The sum of the loads carried by these two corners make up the crossweight percentage, and anytime this percentage is increased, we tighten the car. To fix this, increase the rebound in the LR shock and/or soften the compression in the RF shock.
Chassis roll moves the upper...
Chassis roll moves the upper ball joints to the right, changing the front cambers so that the LF loses positive camber and the RF loses negative camber.
2. Spring Rates The spring rates in the car may contribute to a tight condition on entry. If the front spring rates are split so that the RF spring rate is higher than the LF spring rate, then an effect similar to that described above (with the shock rates) takes place while braking.
The stiffer RF spring causes the crossweight percentage to go up as we enter and brake into the corner and the front end dives. Reducing the spring split across the front to reduce the effect of increased crossweight percentage during braking on entry can make the car more neutral on entry.
3. Brake Bias Imbalance Again, make sure your brake bias is tuned correctly. If too much of the bias is on the front brakes, the car will push under heavy braking. If indeed brake bias is a problem, then lightly brake into the corner; it should get better.
4. Lack of Antidive If the car is diving excessively under heavy braking, the RF wheel will lose camber quickly and the tire will lose both footprint and traction. Antidive properties can help the situation. Although the camber change is quick and the wheel's camber settings return to normal a short time later, once a push starts, it is hard to stop it without slowing down.
Chassis dive pulls both top...
Chassis dive pulls both top ball joints toward the centerline of the car and changes the camber, with the LF losing positive camber and the RF gaining negative camber. The action of rolling and diving can cancel each other out at the RF wheel and result in a desired lack of change in camber through the turns.
For the BBSS asphalt setups, the LF wheel loses a good deal of camber and the RF wheel gains a lot of camber.
We want to eliminate as much of the camber change as possible by designing antidive into our front suspension. If we angle (from a side view) the upper control arm shaft that is mounted to the chassis so that the front is higher than the rear, we will have introduced some amount of antidive into the front suspension. We can also create more antidive by raising the rear chassis mounting point of the lower control arm, although this has less effect than angling the upper control arm shaft.
5. RF Camber Change The RF wheel will always experience movement as the car enters and rolls into the turns. If the front geometry is not designed correctly, then the RF camber relative to the racing surface will change as the car dives and rolls into the turns, and the tire will lose grip.
In testing over a five-year period, it was discovered that most tires "want" little or no change in RF camber relative to the racetrack surface as the car dives and rolls. We cannot read this type of camber change merely from bumping the wheel because the added effect of chassis roll on camber change is missing when we do that. Many of the geometry software programs on the market will allow you to simulate chassis movement and see the true camber change.
We have now tuned the car for the middle phase first, then the entry phase. This represents the most logical progression in refining the setup in our cars. The middle handling influences both entry and exit, and entry performance can influence midturn handling.
In Part II of "Basic Handling Solutions," we will explore the problems associated with the exit phase. Many racers believe the problems that occur here can be the most detrimental to performance in an actual race. That is because in practice, we never have to pass another car in "anger."
Problems involving the exit while accelerating can be managed better when we are by ourselves, but in the race, we need the car to turn well and to have good bite as we drive up and under another car. If the push or "loose-off" condition rears its ugly head, it will prevent us from moving up through the field.