To win races, the car needs to handle at every point on the track. The turns are key areas
Good handling is often thought to be a car that is neutral as it runs through the entry, middle, and exit of the corner. While that may be fine as a goal, what we really want is a balanced and neutral setup that will stay consistent throughout the race. When the car is not neutral, there are some good, and some not so good, ways to make it neutral. Here, we will examine the problems associated with a poor-handling car 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), known by road racers as oversteer and understeer. For our purposes, we'll stick to the circle track lingo. The tight or loose condition can be in either of the three phases of the turns: entry, middle, or exit, or any mix of the three. The cure must address where the car isn't handling and ideally not affect where the car is good.
We will look at each phase of the corner and present handling fixes based on what the car is doing at each point. We will 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 good in the middle, we might have solved some of the entry and exit problems. Usually, improved mid-turn handling offers the most gain in overall track performance and that is why we start there and make sure that segment remains good if we need to make changes to improve the other phases.
We divide the turn into three phases or segments. This way, we can concentrate on the way
Mid-turn handling problems can be caused by a car that is either tight or loose. By far, the most common handling malady is when the car will not turn. This can be caused by several different conditions, or a combination of several. We will need to go through a checklist to eliminate some familiar problems. The following is, in order of significance, a checklist of things that can make the car not want to turn.
1. Front Moment Center
Location-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 that is midway between the tire contact patches. The farther to the left the MC is located, the more the front end 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 setup with a MC more to the right of the 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 than would cars with a higher CG.
The moment center (sometimes called the roll center) location is very important in determi
2. Excess Ackermann
In the front end geometry related to steering, 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 to the left. The opposite of Ackermann is called Reverse-Ackermann. That is an effect that causes a decrease 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, intentionally 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 help the situation. We must eliminate most of the Ackermann. The fix is different for the two most common types of steering systems we find in circle track stock cars.
The amount of Ackermann in our rack-and-pinion steering system can be regulated by moving
In the rack-and-pinion steering system, if we have equal length steering arms (the arms that are attached to the spindle that the tie rods are bolted to) 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, 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.
A common fix, and one that is not recommended for dirt cars because those cars have to steer both ways, is to change the lengths of the steering arms so that one spindle will turn a different number of degrees than the other. If we have Ackermann present in our car, we can lengthen the left steering arm to slow that spindle down and/or shorten the right steering arm to speed that spindle up. Again, this only works to reduce Ackermann when we steer to the left. If we do this and then steer the car to the right, the opposite occurs and we gain toe because the right wheel will turn faster than the left wheel increasing the amount of toe-out.
On a 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.
We can change the amount of Ackermann in our drag-link steering system in a way similar to
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 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 in line.
4. An Unbalanced Setup
A loose or tight car can also be caused by a tight or loose setup. These 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.
If the average of the front tires is hotter than the average of the rear tires, the car is probably tight and may have too much crossweight percentage in it. The car should respond to a reduction in crossweight.
The primary goal of all setups is to develop a balance between the two ends of the car so
In the case of an unbalanced setup causing the 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 spring. That, too, will reduce the rear roll angle. We can stiffen the right rear spring and/or reduce the left rear spring rate, if we are running on a banked track of 12 degrees or more, to reduce the rear roll angle.
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. We can soften the right front spring, stiffen the left front spring or run a stiffer left front spring than the right front spring on flatter tracks. The stiff left front spring setup does not work well on tracks banked over 10 degrees. Changing to a smaller sway bar does increase the front roll angle, but not very much. We mostly use the sway bar to tune for traction off the corners.
5. Crossweight Percent
Crossweight percent is defined in circle track racing as the total of the right front and left rear wheel weights added together and divided by the total vehicle weight. If everything else is correct, such as alignment, balance, camber change, etc., and the car is still tight or loose, then the crossweight percentage is probably wrong for the weight distribution in the car. For a tight car, reduce the percentage of crossweight and for a loose car, increase the crossweight percentage.
If the rear end is positioned so that it is aimed to the right of the centerline of the ca
A balanced car is evidenced by matching the tire temperatures. The front and rear averages should be close to the same (adding the front two tires and comparing to the rear two tires), as well as each of the side tires should be nearly the same temperature from front to rear. For example: LF + RF = LR + RR, LF = LR and RF = RR. Work to get these temperatures correct and then fine-tune with the crossweight percent.
A Loose Setup
A loose condition at the mid-turn phase is where the car turns well but the rear end is not gripping as well as the front. The feel of the car as well as the tire temperatures can tell a lot about what is causing the loose condition.
A loose car will usually have a right rear tire temperature that is hotter than the other three tires. A loose car will not have enough traction off the corners and will spin the rear tires, especially the right rear tire. Here are several probable causes for a loose car:
The rear control arms are positioned so that as the chassis moves vertically in the turns,
1. Rear Alignment
The very first consideration is rear alignment. If the rear end is out of alignment with the right rear wheel farther back than the left rear 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.
2. High Rear Roll Center
The Panhard bar, or whatever represents the rear roll center, 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.
The rear springs may be too stiff, resulting in the front wanting to roll more than the rear. While this is not a common occurrence, it is possible. Soften the rates of the rear springs. Soften only the right rear spring if running on a flat track. This has a large effect, so be careful. The car can change to being tight in a hurry.
If you are able to setup the car so that it is good through the middle of the corner, then we need to work on entry performance next.
A useful design tool is anti-dive (A-D), which keeps the front suspension from moving too
A car that is loose into the corner may have any one of, or a combination of, several problems. Let's look at the most common causes of a stock car being 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 set 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 left rear shock may be too stiff in rebound or the right front shock may be too soft in compression which lifts weight off of the left rear wheel on initial entry under hard braking. To fix this, reduce the rebound in the left rear shock and/or stiffen the compression on the right front shock.
3. Brake Bias Imbalance
Make sure your brake bias is tuned correctly. If too much of the bias is on the rear brakes, the car will be more loose 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.
Chassis roll moves the upper ball joints to the right, changing the front cambers so that
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 right rear wheel is farther to the rear than the left rear wheel, we have rear steer to the right. This makes the car very loose and we need to adjust the suspension components so that it will not steer in this manner.
If the car is a dirt Late Model and the track is very dry and slick, 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.
1. Improper Shock Rates
The left rear shock may be too soft in rebound or the right front shock may be too stiff in compression which will tend to load the right front and left rear tires on initial entry under hard braking. These two corners make up the crossweight, and anytime we increase the crossweight percent, we tighten the car. To fix this, increase the rebound in the left rear shock and/or soften the compression in the right front shock.
2. Spring Rates
The spring rates in the car may contribute to a tight car on entry. If the front springs are split so that the right front spring is higher than the left front spring, then an effect similar to the shock notes above takes place. The stiffer right front spring causes the crossweight percentage to go up as we enter and brake into the corner. Reduce the spring split across the front to reduce the effect of increased crossweight percent on entry braking.
Chassis dive pulls both top ball joints in towards the centerline of the car and changes t
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 you lightly brake into the corner, it should get better. That is one way to tell if the front has excess bias.
4. Lack of Anti-Dive
If the car is diving excessively under heavy braking, the right front wheel will lose camber quickly and the tire will lose traction. Anti-dive properties can help the situation. Although the camber change is quick and the wheel returns to normal camber settings a short time later, once a push starts, it is hard to stop it without slowing way down.
We want to eliminate the camber change by designing anti-dive 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 anti-dive into the front suspension. We can also create more anti-dive by raising the rear chassis mount of the lower control arm.
5. Right Front Camber
Change -The right front wheel will always experience movement 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 right front camber relative to the racing surface will change and the tire will lose grip. In testing over a five-year period, it was discovered that most tires want no change in camber relative to the race track surface as the car dives and rolls. We cannot read this type of camber change merely from bumping the wheel because the effect of chassis roll on camber change is missing.
The next segment of the track we will explore in Part Two is the exit portion. Many racers agree that the problems that occur here can be the most detrimental to performance in the actual race. In practice, we never have to make a pass in "anger." Problems with exiting under power can be OK when we are by ourselves, but in the race, when we need for the car to turn well or to have good bite off as we drive under a car, that push or "loose off" condition rears its ugly head and prevents us from moving up through the field.
Next time, we will examine ways to fix exit woes.