Many of the articles you read in Circle Track cover chassis setup, areas of critical concern, one at a time and over the years we have tried to refine and update the information. In this installment, we will present the top chassis challenges you will face when setting up your race car. If you can manage to refine these 13 challenges, then we believe you will be well on your way to success.
In the example shown above of a Drag Link system, we see why it is designed as it is with
1. Steering Challenges
A correctly designed steering system is an essential element in the make-up of a winning stock car. The amount that each wheel turns as the car is steered can have a major impact on how your car will handle.
The amount of static front end toe you need largely depends on the size of the racetrack, the banking angle, and the type of tire being used. Regardless of the amount of static toe-out you use, the toe numbers can change as we turn the steering wheel.
If our car gains toe when it is steered then we have what is called Ackermann effect. If our car looses toe when it is steered, we have reverse Ackermann. In today’s race cars, we do not need the Ackermann effect. Static toe provides all of the required difference in steering angle we will need to negotiate the turns.
This is a very clever idea we came across. This team drilled and tapped the spindle and we
2. Spindle Challenges
Many times we are faced with incorrect arm angles for proper Moment Center design because of a spindle that is either too short or too tall. If we can find a spindle with different dimensions, we may be closer to having the correct arm angles.
If we change from a 73/4-inch tall spindle, with an offset of 31/2 inches from the bottom of the spindle to the center of the pin, to an 81/2-inch tall spindle with a 31/2-inch offset from the bottom to the pin center, then we have raised the upper ball joint by 3/4-inch and not changed the lower control arm angle.
We can also install a 91/4-inch tall spindle with a 41/2-inch offset from the bottom to the pin and gain 1/2-inch of height of the upper ball joint while lowering the bottom ball joint by 1 inch. This does two things, it increases the upper control arm angle and also reduces the lower control arm angle.
At any rate, be aware of the different spindle designs related to the changes you may need to make to refine your MC design. Always keep in mind that spindles are very easy to change and you should never get locked into using a specific spindle. Rather, install what will make your car work better.
Be very careful to align the brake brackets before welding. Check them carefully after wel
3. Brake Challenges
In my experience, you can get all of the information concerning the proper choosing and use of brake components for your type of racing from your racing brake supplier and/or manufacturer. What is probably more important than components is the installation of the brake brackets.
This is an area where brake pros can’t help you. Many times we see where a car builder or team will hastily install the brake caliper brackets and not take the time necessary to insure the proper alignment and spacing. This will provide problems that are impossible to fix unless we address the real problem.
Take the time to do a good job of aligning the brake mounting brackets so that the pads will be perfectly parallel to the rotor and that the pads are spaced equally on each side of the rotor. This will provide smooth and efficient braking from now on.
The Moment Center controls the dynamics of the front suspension in a double-A arm suspensi
4. Moment Center Challenges
The growth of information about the front moment center during the last several years has helped us to understand the way in which this invisible point controls the front dynamics of our race car. We have defined exactly what the MC does and where it should be located
The primary reason why two seemingly identical cars will handle differently can often be traced to a front MC that is in a different location from car to car. Knowing the role of the MCs and being willing to make changes so that our MCs are in the right position is one of the very first and most important steps we take to achieve the total handling package.
Front wheel camber change is influenced by both chassis dive and chassis roll. It is the c
5. Camber Challenges
Using excessive or deficient camber in either of the front wheels can be one of those racing crutches that can mask other problems. This usually means that the car has a setup and/or geometry design problem that is causing incorrect weight transfer or incorrect camber change during cornering.
The most useful definition of Camber Change is the deviation from the static camber that happens when the car enters and negotiates a turn and goes through a combination of dive and roll of the chassis. The number of degrees of camber that the front wheels lose or gain relative to the racing surface from static (down the straightaway) to dynamic (in the middle of the turns) chassis attitude is true camber change.
If we try to determine the amount of camber change by bumping the wheel with the car at static ride height, we will not see a true picture of our camber change characteristics. The true camber change relative to the racing surface, which is all the car knows, results from a combination of roll effect and dive effect measured together in combination.
It’s a good idea to buy or borrow a good quality spring rating fixture so you can accurate
6. Spring Rate Challenges
The primary components used to set up a stock car are the springs. When we have chosen the correct spring rates, in conjunction with well designed Moment Centers and weight distribution, then we get what we want—a balanced and fast race car.
All too often we crutch the car using inappropriate spring rates and weight distribution that will serve to provide neutral handling, but not yield the desired result of consistency.
The very first thing to consider when talking about springs is, what is the exact spring rate at each corner of your car. You must test each spring and do it in the proper way. You need to know the spring rate of your springs at the ride height and range that they will be working in the car.
Make sure of your spring rates, replace bent or fatigued springs, and always know your wheel rates when altering the mounting points or transferring the setup from one car to another. The car basically rides on four springs and the more we know about how they work in our cars, the more accurately we can develop a winning setup.
7. Shock Challenges
Shock selection can enhance or ruin a good setup. We should never try to solve basic setup problems with odd selections of shocks. What we have learned over the past decade is that using shocks to overcome mid-turn handling problems can be frustrating and futile.
Solve your setup problems first before experimenting with shocks. Never crutch a bad setup. Most shock technicians will tell you to put standard rate shocks on the four corners until the setup is sorted out. Then make changes to one corner at a time to see and feel the results. The most important task is to make the driver more comfortable and that will translate into faster lap times.
And, shocks should work in conjunction with the spring rates you have. If you are running on bumps, find the spring rate for the bump and use a shock that will work with that spring rate if that is what the car will use through the turns.
With the rearend steering to the left of centerline, the rear of the car will want to run
8. Rear Geometry Challenges
Rear steer in a circle track race car is a condition caused by suspension movement. Under the right conditions, RS can be beneficial and enhance performance. Under the wrong conditions, it can ruin your handling. We need to have a solid understanding of what produces RS and what effect RS has on the handling in our cars.
The first and foremost thing to understand about RS is that it is caused by rear suspension movement. As the rear corners of the car move, along with the controlling arms that locate the rearend fore and aft, each side can move the wheel on that side forward or to the rear.
Obviously, if both of the wheels did not move or moved in the same direction by the same amount, we would have zero rear steer. It is when one wheel moves more than the other that we have rear steer.
On asphalt, don’t make large changes to components that influence rear steer. Make small adjustments if you feel you need to and once you find the correct amount of rear steer, stay there and tune the handling with the other components.
When racing on dirt, watch the conditions and be prepared to make changes accordingly, not just to the setup, but also related to rear steer. That way, the car will stay fast and balanced throughout all of the changing conditions.
9. Bite Challenges
If there is one thing we usually can’t get enough of it is forward bite in our race cars. We need to learn ways to make the tires stick while we are under power off the turns.
An opposing pair of tires (tires on the same axle at the same end of the car) will develop maximum traction when they are equally loaded. The closer we can get a pair to being equal, the more traction they will have.
The shape of the track for both dirt and asphalt can influence the available traction in several different ways. As we apply power, we need to know a little about how the track is banked, how the banking angle is changing coming off the corners and how the radius of the turn might be changing.
The tracks we worry about getting off the corners are the ones that are flatter and with less surface grip. When all available and useable methods of promoting traction have been applied, the car may still be difficult to apply power to without losing rear traction. In that case the drivers must use their skills to help prevent loss of rear traction coming off the corners.
Many top drivers have perfected the art of throttle control to help maintain traction. This means that if the driver knows he/she can’t apply full throttle without the rear tires spinning, then they will work to apply just enough power to accelerate without breaking the tires loose.
When we are cornering, a lateral acceleration force commonly called a G-force tries to ove
10. Weight Distribution Challenges
In order to really understand race car handling, we must know something about the load distribution on the four tires and how those loads change through the course of a typical lap. When we fully understand the principles of weight distribution and load transfer, we can better plan out our setup so that our car will have a better load distribution when cornering.
The extensive studies of the properties of tires all came to the conclusion that a pair of tires will produce more combined traction when they are evenly supporting the weight upon an “axle.” The axle term is used here to mean any two opposing tires in a suspension system.
The relationship between the two suspension systems will dictate how that transferred load ends up being distributed upon the four tires.
As we make positive changes to bring our car to a more balanced setup, we will need to make corresponding changes to the crossweight percent. Reducing front roll stiffness causes more front traction and the crossweight percent must be increased to keep the car from becoming loose. Increasing the rear roll stiffness will also cause the same effect, so too is the need to up the crossweight percent.
Don’t get stuck on a particular crossweight percent number. Be flexible and understand what is happening when you make those spring rate changes or Panhard bar movements or when you move weight around in the car. If you understand the influence of weight distribution and load transfer, you can then make more intelligent chassis setup decisions.
The alignment of the driveshaft to the transmission output shaft and the pinion shaft shou
11. Pinion Angle Challenges
In the past, pinion angle has been measured relative to the ground. This approach does not represent the true picture of PA. What should be of concern is the angle of the driveshaft to both the pinion and the transmission output shaft.
When the U-joint operates with any amount of drive line angles, it has a problem. The bearings speed up and slow down twice per revolution of the driveshaft. This causes an oscillation in the powertrain. The more angles that we have, the higher the peaks of oscillation we see and therefore the greater chance of vibration.
Driveline angles are a cause of vibration and power loss. If your race car must have drive line angles from a design standpoint, the angle of the driveshaft to both the transmission output shaft and the pinion shaft should be equal and also opposite. The angles should be kept to a minimum when at all possible.
Driveshaft angles are not only measured from a side view, but also from a top view. Some offset late-model cars can have as much as a 11/2 inch displacement of the rear of the driveshaft from the front. That equals almost 2 degrees of driveshaft angle at both the transmission and the pinion. So, we can align the driveshaft, from a side view, to zero angle and still have 2 degrees of overall driveshaft angle present.
This is what we should end up with after aligning the rear to the right side tire contract
12. Alignment Challenges
Poor alignment can ruin an otherwise great setup. How critical is whole car alignment? It is very critical. Four-wheel alignment can be the final setup parameter that can take you to the front or keep you in the rear of the field.
The problem is that no amount of manipulating the other setup components will overcome a wheel alignment problem. While it is probably true that a car out of alignment is more forgiving on dirt, it is still very important for both dirt and asphalt to have your wheels properly aligned.
This whole process of aligning your race car should only take about an hour or two if there are several team members helping. That is very little effort expended to make sure your car will track correctly.
The Roll Angle Analysis Method allows us to understand that each end of the car wants to r
13. Setup Balance Challenges
In past articles of Circle Track we have used the term balance when referring to setups. The balanced setup has noticeable results in performance. That is why we are so adamant about getting our readers to fully understand the concept.
There are several critical reasons why a balanced setup is essential to optimum chassis performance. First of all, we can accurately predict load transfer if the setup in the car is balanced.
Secondly, we will have less (almost non-existent) chassis flex with a balanced setup. Compliance, or flexing of the chassis, can’t occur if we remove the forces that force this to happen.
Last, and most importantly, a balanced setup is much more forgiving when the track conditions change or the driver runs different grooves. The speed of the car does not fall off as much, either, as the race goes on and the tires wear. It is the tendency of the balanced setup to help maintain a neutral handling characteristic and retained speed after a long run that helps win races.
Whichever type of racetrack, and whether you run dirt or asphalt, attention must be paid to the relationship of the front suspensions desires to the rear suspension desires. When both ends are close to wanting the same attitude in the turns, then all four tires will be doing more work and the car will be faster and more consistent.
For the specifics about each Challenge, dig out your old copies of CT and read the related articles. For your convenience, Motor Books International has compiled a group of chassis related articles that have appeared in CT over a four year period in a book titled Chassis & Suspension Handbook. And, keep reading CT for updates and presentations on advanced chassis setup techniques and cutting edge breakthroughs.