Mart Nesbitt recently earned his first win in the Hooters ProCup Series in the Lucas Oil 2
Over the years, teams have invented varied ways to set up a stock car. The overall goals, we assumed, were two-fold. First, we all desired to put down the fastest lap among our group of competitors. We also wanted to create a "balanced" race car, meaning the car neither pushed nor was loose. Even if we were able to achieve both of these objectives through a process of trial and error, we still may not have found the ideal setup that would win races.
We have learned the fastest setup on a two- or three-lap run is not usually the fastest setup at the end of the race when running on worn and hot tires. The key to finding the best setup is understanding that our fast setup must remain fast over a long period of time-ideally until the checkered flag falls. The key to that end is to understand the true definition of "balance" so that we can have the desired consistency needed to be a winner.
If you have ever made changes to your setup for handling better, suspecting all along that the real problem was somewhere else, then you have "crutched" the car. This term means that what you are doing to help the car be neutral in handling is not likely the best fix for the problem.
He worked long and hard at correcting all of the chassis problems that plagued his car unt
For many years, and even still today, racers have developed some pretty ingenious ways to "crutch up" their race cars to make them handle better. Handling, in our most basic understanding of the word, can best be described as being able to drive through a turn without the car being either loose (driver looking at the infield) or tight (driver looking at the outside retaining wall). The three main segments or phases of the turn where we might experience handling problems are entry to the turn, through the middle, and upon exit off the turn.
A race car setup crutch could be defined as any change in the setup that is intended to solve a handling problem that, in reality, does not make the car faster and/or causes other problems to appear at other points on the racetrack. We will explain how some specific crutch methods work and why racers think they need these particular crutches. In future articles, we will expand on each topic to explain how to develop more efficient ways to accomplish the same goals.
Here are the top 10 setup crutches:
The balance in his car showed when he was challenged and the car never wiggled or failed t
The way the driver is forced to drive the car can sometimes be a crutch. How many times have we heard a driver say that the car is loose when we can see it appears tight on entry and in the middle of the turns? The driver is most likely steering excessively, trying to overcome a tight condition, but unaware of his action. This excess steering definitely creates more traction in the front tires to help balance the car. Here is why.
The way the driver is forced to steer the car can be an indication of a problem with the setup. This is one of the top indicators that might lead to a crutched setup. A lot of research has been done on tire characteristics related to traction. Tire engineers learned that a tire will generate more traction at increased angles of attack in the direction the car is turning. This means that the front tires will actually gain more traction as the wheel is turned farther left, up to a point.
When the steering gets to an excessive angle of attack, the front tires will suddenly give up all of their traction, causing a severe push. Normally, as the steering wheel is turned a few degrees more than normal to force the front end around in a tight car, the handling balance begins to change.
We should think of the turns as three distinct phases or segments. In doing so, we can eva
As the driver enters the turn, backs off the throttle, and applies the brakes, he (or she) begins to turn the steering wheel and must turn it sufficiently for the front end to come around. If the car is actually set up too tight, the driver will need to turn the wheel further than what would normally be necessary in a car that is neutral in handling balance. When the driver has turned too far, the traction balance reverses from tight to loose as the front traction begins to exceed the rear traction. At this point, the car will start to feel loose. This can happen so quickly that the driver will swear that the setup in the car is loose.
Just past mid-turn, the car will definitely feel loose to the driver. The exit performance off the turn will also suffer as the driver gets on the throttle and the car gets looser from power-induced rear wheel spin. The average temperatures of the rear tires will then probably be hotter than the average of the front tires due to spinning the tires with the loose-off condition. The crew will many times read this as a loose condition and think the car needs to be tightened up. It is already tight, and so a lot of valuable time is wasted searching for solutions to this basic problem.
A great way to quickly discover just what the handling balance really is for your car is to have the driver roll through the turn below the maximum speed. The amount of steering input needed to just drive around the turn should be mentally noted. The crew chief can view the location of the driver's hands from the fence or the top of the hauler. Then, the driver should take the turn at full speed as he would in the race. Again, note the amount of steering input by asking the driver or looking at the position of his hands at mid-turn. If the steering wheel is turned more than when the car was rolled slowly through the turn, the car is set up too tight. Many drivers are very surprised at the outcome of this test. A lot of time can be saved by doing this simple exercise.
We can see where the driver's hands are located when the car is normally turning the corne
We are often in search of more bite off the corners. One way to accomplish that is to soften the right-rear spring. If your car is too tight in the middle, the rear springs may be too soft or the spring split may be wrong for the type of racetrack you are racing on. A softer right-rear spring than the left-rear spring can make a car very tight if other components are not set to balance the car.
There are many ways to promote more bite off the corners rather than by putting excessive rear spring split in the car. Often, a small amount of spring split will do the job while helping to maintain balance setup for mid-turn performance.
The front springs may be too stiff or the spring split may be wrong, causing an unbalanced setup. A stiff right-front spring can make the car too tight by not allowing the front to roll to work with the rear.
In this example, when at speed, the driver's hands are well below the top of the door sill
The way the front springs are arranged as to stiffness is dependent upon the track configuration and banking angles. If the track has a long and larger radius entry combined with a lower banking angle, you can run a softer right-front spring than the left-front spring. This serves to improve turn entry and helps make the front end more efficient at mid-turn. This will not work with a tighter entry combined with a higher amount of track banking angle.
For tracks with medium banking and normal entry characteristics, you can run even spring rates across the front with good results. As the track banking angle increases, so should the right-front spring rate over the left-front spring rate.
Sometimes, we may play with the upper control arm angles and lengths to see if we can improve the way the front end works. When we do this and do not track the moment center (often referred to as the roll center) location, we can drastically change the dynamics of the front suspension for the worse. There is no telling where the moment center (MC) might be located after we make our changes.
The front moment center location controls much of the dynamics of the front suspension.
The front MC is the bottom of the front moment arm. Its position determines the length of the moment arm and the efficiency of the front suspension. If the front moment center were located too far to the left, the front suspension would roll excessively and the right-front suspension travel would be excessive. This will cause the right-front tire camber to change too rapidly and that tire would lose grip, a condition usually described by the driver as the car "falling over" on the right front. If the MC is located too far to the right, the front end will be overly stiff and not want to roll, and the front suspension will not work along with the rear. This is much the same as having stiff springs up front.
The static front wheel cambers we run to maintain proper tire temperatures across the face of the tread is an indicator of the balance of the setup and/or possible problems with camber loss or gain at the right-front wheel. Running excessive camber on the right front tells us that tire is working too hard.
This invisible intersection point is the bottom of the moment arm and should be designed c
For any type of racing, be it dirt or asphalt, high or low banking, we should never need more than four degrees of negative camber at the right front. Teams that run 5-6 degrees of static camber are usually running setups that are unbalanced and that cause an excess amount of weight transfer to the right-front tire.
Just like the front MC, rear MC is the bottom of the rear moment arm. If the Panhard bar is set too low for the springs selected, the rear of the car will be too "efficient" and want to roll more than the front. This causes a tight condition due to excess weight transfer to the right-front tire.
The Panhard bar, J-bar, leaf spring, or Watts link heights determine the rear moment center height. Since the MC is the bottom of the moment arm in the rear of the car, its height determines the moment arm length. The longer the moment arm (due to a low MC height), the more efficient the rear suspension will be and the greater roll angle the rear will want to attain. As we raise the rear MC through whatever means, we shorten the rear moment arm and decrease the efficiency of the rear suspension causing it to be stiffer, similar to putting stiffer springs in the rear.
The car "feels" the rear moment center halfway between the tops of the springs and at its
The changing of the rear MC height is one of the primary tools we use to help create a balanced setup where the two ends of the car are working together in harmony.
Having an excessive amount of crossweight percent, or bite as it is referred to in dirt racing, causes too much weight to be supported by the left rear and right-front tire and can cause a car to be tight in, through the middle, and off the turns.
Running a crossweight number that is too low is a distinct indication of a tight car. If a car needs 51.2 percent crossweight to have proper weight transfer, and is only running 48.8 percent, the team has needed to take cross out of the car because the setup was tight.
There is an optimum percentage of weight supported by the cross corners (right front and left rear) that will make the car neutral. Remember, a neutral car is not necessarily a winning car. It must remain neutral throughout the entire race.
If the steering system creates either too much Ackermann (where the left wheel steers much more than the right wheel in a left-hand turn), or reverse-Ackermann (the reverse effect), the car will have too much toe-out or toe-in at the point of mid-turn. This will cause the front tires to desire to go in different directions and they end up fighting with each other. This will cause one or both of the front tires to lose grip, which makes the car feel very tight to the driver.
Rear stagger is the difference in circumference of the two rear tires. The left-rear tire
Some cars running on smaller racetracks will need small amounts of Ackermann. Remember that one degree of Ackermann, meaning that the left wheel turns a degree more than the right wheel at mid-turn steering angles, represents a full 1/2-inch of toe. If we start with 1/8-inch of toe and add another 1/2-inch, we would have a staggering 5/8 inches of toe at mid-turn, which is too much.
On the smaller tracks, we could stand to gain 1/8- to 1/4-inch of toe to compensate for the small radius turns. We are causing the front tires to work against each other when we run more than that.
Insufficient rear tire stagger will cause the car to "point" towards the outside wall on exit. There is a correct amount of rear stagger for each track based on the overall tire diameters, track width of the rear tires, the radius of the track, and the track banking angle.
Too little stagger will cause the car to drive to the right as we get back into the throttle and the rear end moves on an arc that has a greater radius than the track at that point. The larger radius, if drawn onto the racetrack, would lead into the grandstands and that is definitely not where we want to go.
The rear end should be aligned so that it is perpendicular to the centerline of the chassi
Another setup crutch is the use of excess brake bias at either end of the car to help solve a handling problem. If a car is tight or loose on entry, many drivers have learned that if they make changes to the brake bias, they can improve the handling and performance at that one point on the racetrack. While that is possible, it can lead to problems at other sections of the turn. Using the old trial and error routine, the driver will say the car feels better on entry with the different brake bias, but now wants to work on the mid-turn handling balance, which has gone bad.
So, more changes will need to be made to attempt to solve other newly created problems where those problems did not exist before. It's not hard to see that using a brake bias crutch to solve one problem can lead to more and more problems. Soon, the team is overcome with a complicated series of handling problems while the car is getting slower and slower.
We know the rear end should be aligned perpendicular to the car's centerline and inline with the right-side tires. If the car is tight, some teams will move the right-rear wheel back to help "free up" the car. Steering the rear end either by static alignment or by invoking rear steer to the right will definitely help make the car less tight, but at the expense of exit performance.
If the car is loose, a team might move the right-rear wheel forward or design more rear steer into the left to help tighten the car, but more often than not, the alignment will make the car too tight especially on exit off the corners.
There is an optimum amount of stagger required for each car running at each racetrack that
The use of the excess steering input or abnormal brake bias or any other of these crutches are indications that other problems exist and need to be fixed. What the car needs is an arrangement of spring rate layout, front geometry design (including moment center placement), Panhard bar height (rear moment center height), proper steering characteristics, correct weight distribution, and tire stagger, that will all work in combination to provide a fast and balanced setup. The last things to work with are finding the correct shock rates for optimum entry and exit transitional handling, the correct front-tire cambers, and the correct tire pressures, the latter two being adjusted based on the tire temperature readings.
Once all of these areas of setup are correctly identified and made to work together, the car will give the team what it wants, a fast and consistent handling package that the driver can use to win races.
When you identify your driving and set-up crutches and find the best fix for your handling problems, you and your crew will be more successful and have a lot more fun at the racetrack.
Coming Next Month: Camber Crutches.