Chapter 6

Making the Adjustments

This section will integrate the information thus far. This is how the fine tuning of the chassis is done. When reading this chapter remember my layered problem discussion from the Introduction part of this book. The changing a spring rate won't work if the alignment is wrong and vice versa. All the adjustments have to be right simultaneously. But when they are all right, the car becomes very sensitive to any one of these adjustments. This phenomenon is what makes this sport such a challenge. You have to get all of the adjustments right at the same time.

This is why, as discussed in the Introduction section, understanding the theory and applying it practically are two different disciplines. All persons are not able to do both. Making the adjustments calls for a good troubleshooting person to discern the layers of problems that can occur. It takes teamwork.

Handling vs. Cornering Power

This section has a couple discussions concerning Handling vs. Cornering Power. Handling is defined as how the car responses to the driver. Handling expresses controllability and Cornering Power amount of centrifugal force the car can generate. As track conditions (say more slippery) change, the car setup needs to change. If the car does not develop the cornering forces because it is slippery, the car's handling characteristics will not change as they had before. The wheel rates cannot be the same because the same cornering (centrifugal) force is not being attained. This means you put even stiffer springs in the front so same tire loads will happen at a lower cornering force.

By no means is this a complete list of scenarios that could happen, but the scenarios listed are typical.

• We achieve most of our handling characteristics by varying the wheel rates. The beginning driver would want a lot of stiffness in the front because it makes the car understeer or push. An understeering car is much easier to drive, but does not have a lot of Cornering Power because the front Ct (grip) varies so much. As the driver becomes more proficient, the driver will want to soften the front wheel rates, gaining Cornering Power, but sacrificing handling and controllability.
• Left side bias is a good way to achieve maximum Cornering Power. It has at least two hidden pitfalls though. But if you have the right amount of left side bias the tire loads will equalize in the corner thus yielding the most Cornering Power. It can really improve your Cornering Speed. Here is a list of left side bias pitfalls:
• The change in tire loads that change the Cts does not care if you are turning or not. When you enter a corner with left side bias the weight is already transferred but in the wrong direction and the car's handling characteristics are how they are until you can transfer weight because of the cornering force. The risk is that as the weight transfers there will be some handling characteristics that you cannot drive.
• Cars with a lot of left side bias can be hard to drive in a straight line. There is so much weight on one rear tire and so little on the other rear tire that the car will spin out with very little power applied.
• Left side bias also causes chassis/body roll, which causes wheelbase and camber changes.

Alignment

This section is discusses a few alignment concerns and a short alignment procedure. Alignment (direction) of the tires is very important. The tires must point in the proper directions. Alignment is not a straight forward subject.

The front is toed out like this picture. No amount of calculations thus far can prove any benefit of using toe out. The toe out would make the tires work against each other. Therefore, their Cornering Power is wasted. This alignment may be beneficial at times, if the car is not working and you don't have the tires or springs you need to adjust it properly, toe out can make it push for you.

Aerodynamics

Empirical (based on experiment and observation) is the word on aerodynamics at every level of auto racing. There are very few formulas that can be practically applied. Even very well financed teams will rent a wind tunnel and test their ideas. Then everyone else tries to copy what these leading teams are doing.

There are two considerable forces caused by aerodynamics. They are Lift, which can be up or down, and Drag.

• Drag can be described as a Coefficient of Drag times the Frontal Area of the car times ((the Air Density + the Speed squared) divided by 2).
• Lift, hopefully as a down force, is added directly to the tire loads. This down force does change the Cts of the tires in the same way that other loads do. But a freebee, because the down force because of aerodynamics is not associated with any mass, therefore, it is free Cornering Power.

Here is a list of aerodynamic practices that usually cause down force:

• A body with a low front and an open back panel.
• Wings and bi-wings.
• Side dams that keep air from flowing off the top of the car.
• Large side dams on the inside of the car keep the car from going sideways.
• And a spoiler on the rear deck.

Tire Selection

Tire selection is not always straightforward, that is, softer is not always more traction. Think of the tire contact as more of a union between the track surface and the tire surface. The ideal union would be if both the surfaces were checkerboards of bumps so that the gripping would be infinite. With softer tires the rubber compresses around the small changes of the racing surface. It nearly completes or fills the checker board. Unfortunately, with the soft tires, the "tire checkerboard" picks up small particles of dust and dirt from the "racing surface checkerboard" which inhibits the surfaces from meshing properly. So pick the softest tire that works.

Dirt tires operate much like the checkerboard surface theory above. But keep this in mind, the Cts (grip) of dirt tires change radically when the tires start gripping the ground below the loose dirt. This is one reason why dirt racing is so challenging. The suspension setup could be totally opposite.

Castor

The dictionary definition of castor is "a small wheel usually free to swivel used to support and move furniture, trucks, and machines." An example of castor is the front wheel on a shopping cart. When you push a shopping cart, the wheel is forced to steer in the direction you push the cart.

Castor is measured in degrees, the amount the steering pivot (king pin) is angled back from vertical. Because the tire patch is located behind the steering pivot (king pin) the cornering side forces will try to unturn the steering. This is why race cars have power steering.

Castor causes the tires to steer in real cars, also. There is a little difference, however, in cars castor causes camber when the steering forces it off its normal position. These camber changes cause slight changes in tire loads. Many times these small changes are enough to influence the car's handling characteristics. The amount of castor is very often used to adjust the car's handling characteristics coming into a corner.

Camber and Steering Stability

Camber also affects steering stability. If the cambers are not equal, one wheel may have more rolling resistance than the other. This rolling resistance changes as the car moves over irregular surfaces. The car will steer because of the irregularities. This is especially true on rough surfaces where the outside of one front tire may catch a bump and the other side does not. The outside of the tire has a lot more leverage on the steering than the inside of the tire.

Rear Tire Stagger

The relative size of the Rear Tires, commonly called Stagger, is an important consideration. Stagger is added in Oval Racing for many reasons.

• To make the car want to turn. While the car is still on the straight, the outside (larger) tire is trying to push the front of the car to the left.
• When the car is in the corner, the tires should not be fighting each other. To achieve this the outside tire is slightly larger, because it is going a slightly longer distance.
• Also, the difference in the size of the tires causes a slight change in the tire loads.

To help you understand what Stagger does, let us review the Coefficient of Traction as defined at the very beginning of this book. The cornering power (c) is the sum of the vectors (c 2 = a 2 + b 2 ). This is a given amount of traction. If the car is going straight then one tire is braking while the other is accelerating, so to speak. This picture shows the forces created by Stagger. The inside rear tire is slightly smaller in circumference, so it does not want to travel as far as the outside rear tire. This creates a drag on the inside which pushes the front of the car to the left. These forces can add cornering power to the front, and subtract cornering power from the rear. In the corner, if the stagger is right, the forces because of stagger should minimize, thus optimizing cornering power.

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