If the moment center is moved to the right, the front suspension of the car tends to get s
Preparing the setup in an asphalt stock car for a new season involves very important processes. Over the winter and early spring, we have lots of time and little pressure so we can properly plan how we will set up our cars. With the right approach, we can have a car that will handle almost like a new one with a much greater chance of success.
The process for dirt and asphalt is similar in some ways and very different in others. That is why we divided the overall theme so that we could address each group separately. The division between the two genres is becoming both wider and narrower, depending on which aspect of chassis dynamics and tuning we are talking about.
I will note when a particular subject pertains to both types of stock car racing. So, all you dirt guys, just because you skipped this article and moved on to your labeled piece doesn't mean you won't have to come back here and take in some of this technology, and vice versa.
The very first step in the process of preparing for the new season is to consider all performance-related items and how they worked last season. Plan changes that could help improve performance or durability, both necessary components needed to win championships. Here are what we consider to be the 10 most important areas of chassis setup.
We want minimal rear steer as the car negotiates the turns. A small amount of steer to the
We always start with the front-end geometry on a stock car, or any race car with a double A-arm front suspension, be it dirt or asphalt. If this component is not set properly, then the whole car suffers, no matter what setup you have in the car.
The dynamics of the moment center and the effects of camber change are very important pieces of the setup puzzle. We have drilled this into you for a long time, and we'll continue to remind you, lest you forget.
The influence of the location of the front MC can be compared to a sliding volume control found on cheap stereos of the past. As you slide the knob to the right, the sound gets louder. Just like that, as you move the MC to the right, the chassis up front gets stiffer. The effect is huge.
Cars that won't turn are very likely to have poor MC designs. I can't tell you how many times I have refined the MC location in a car and had it totally change the way the car turned, for the better. I have had lots of feedback from teams who did the same and had the same results.
You should check your front steering system for the presence of Ackermann. You can do this
The rear geometry layout in your car must be evaluated and set correctly. The control arm angles affect the rear steer, and the third-link angle can redistribute load upon acceleration.
It is not advantageous to have the rear end steer to the right at any time on asphalt. A slight amount of rear steer to the left has been shown to help bite off the corners when needed. But the rear steer must only occur on acceleration and not at midturn.
Generally, you should have the front of your right-side control arm about a third higher than the total amount it will travel in the turns. With setups that use a very stiff right-rear spring, the angle of the right trailing arm will be less than when using a conventional softer spring.
The steering system must be evaluated and any negative characteristics must be eliminated. Negative aspects include excessive bumpsteer (over 0.030 bump in an inch of travel is considered negative by most designers), excess Ackermann (over 1/4 degree added steer in either wheel in 10 degrees of steering input is considered excessive), and incorrect steering quickness.
Eliminate most of your bumpsteer and Ackermann and install the correct steering ratio for your track that would suit the driver. If all of these issues are evaluated and corrected, then you can move on.
The rate of the shocks for compression and rebound should match the spring stiffness you a
It has been found that alignment issues present serious drawbacks to a finely tuned chassis and setup. Alignment issues are defined as: a) rear end alignment, b) contact patch alignment, c) driveshaft to pinion/transmission alignment, and d) engine alignment.
The rear end does not need to be any different in alignment than at 90 degrees to the centerline of the chassis and/or to the right-side tire contact patches. Those patches also need to be in line.
The driveshaft alignment is also critical due to the generation of vibrations and harmonics that are damaging to the bearings and can be felt by the driver. The general rule is that the angles between the driveshaft and both the pinion shaft and the transmission output shaft need to be equal and in opposite directions.
The driveshaft doesn't "know" the view from which these angles are resulting, just that they are equal and opposite. If we have a top-view differential in alignment between the engine (crankshaft and transmission output shaft) and the pinion shaft and they are parallel, then the angle created by that misalignment may be sufficient to provide needed angular differentials.
A 1 1/2 -inch misalignment with a 44-inch driveshaft results in nearly a 2-degree angle at the tranny and pinion shafts. The engine should always be aligned perpendicular to the rear end and/or parallel to the centerline of the car.
If the brake bias is at or nearly out of range for the adjuster in your car, it is time to
The setup we choose for our car needs to be arranged so that the dynamics are balanced between the front and the rear suspensions. Each suspension system desires to do its own thing. Components that affect the desires are: the spring stiffness and spring split, the sprung weight it has to handle, and the moment center location.
Each end has its own moment arm length and resistance to roll as well as other factors. The bottom line is that at midturn, each end will want to roll to its own degree of angle. If those desired angles are different, then we term the setup unbalanced.
Unbalanced setups exhibit certain characteristics, such as an unusually high degree of wear and temperature on one tire versus the other tires. The car may or may not be neutral in handling, but the handling will not be consistent. Work to determine if your setup is balanced and then make the necessary changes to bring it into a balanced state.
Another trick that has been used in the past involves mounting the left spring in front of
Once you have evaluated the above and feel fairly confident that the car is set up correctly, you should then work to tune the transitions with the shocks. The overall work that a shock does is to resist the rebounding of the springs and control the rate of compression. Since the spring promotes rebound and resists compression as its properties, the shock's compression rate must be less than the rebound rate.
The amount of difference is directly related to the installed motion ratio of the spring and the spring's rate. A very soft spring would need more compression rate and less rebound rate, whereas a stiff spring would need a lot of rebound rate and much less compression rate.
Shocks affect the motion of the corners of the car and the placement of loads during transitional periods. If one corner of the car is shocked stiff, then, as that corner desires to move in compression, more load will be retained by that corner as well as the opposite diagonal corner of the car. This will happen during the compression cycle only.
If the same stiffly shocked corner is in rebound, less load will be retained by that corner, as well as its diagonal corner, during the rebound cycle only. That is the essence of shock technology related to handling influences. Plan your shock layout by comparing the shock stiffness to the other corners and to the spring stiffness at the corner you are trying to control.
This diagram illustrates the action and reaction of antidive forces. The braking force tri
Once the setup has been balanced and the shocks are chosen, we need to evaluate our turn-entry characteristics. Brake bias is a very important influence at this segment of the track. We do not want to try to solve turn-entry problems with the brake bias. We just need to make sure the car stays neutral in handling when the brakes are applied.
Brake bias influence can be easily determined by entering the corner with medium to heavy braking first and then entering with light braking to see if there is a difference. If there is, try to adjust the brake bias to eliminate the condition.
Once you have made the entry good, check to see if the adjuster is centered. If it is too far to one side, then changes to the brake master cylinder sizes and/or the pad compounds may need to be made in order to solve the problem while maintaining a centered bias adjuster. Off-centered adjusters can be very inconsistent.
A trick that was developed a few years ago and is still not well known is to stagger the h
In situations where the exit portion of the track provides less traction and/or the corner is more flat, we may have the need to develop more rear traction upon acceleration. Just giving the car more rear traction does not help us if the car becomes too tight in the middle of the turns.
We must develop ways to create more rear traction on acceleration only. There are ways to do that without changing the handling at other points around the racetrack. One way is to have a rear-spring split, where the right-rear (RR) spring has less spring rate than the LR spring. This creates more crossweight as the car squats on acceleration.
Another way to gain bite, which we have described in the past, involves the use of a spring-loaded pullbar that allows a certain amount of rear-end rotation to steer a car equipped with different-length rear control arms. As the rear end rotates on acceleration, the left wheel moves rearward more than the right wheel, creating a slight amount of rear steer to the left.
As the link extends, the rear end moves back, but the left side moves more than the right
Antidive and antisquat are mechanical influences that can help our transitional phases of entry and exit. Antidive helps prevent sudden nosedive on entry by mechanically resisting the downward motion of the suspension using the rotational forces created through braking.
As the brakes are applied, the caliper grabs the rotor and the motion of the wheel/rotor tries to rotate the spindle. This force is resisted by the ball joints (BJ). The upper BJ is being forced in a forward direction, and the lower BJ is being forced in a rearward direction.
If, from a side view, we arrange our arm angles correctly, then the upper BJ would need to move to the rear and the bottom BJ would need to move to the front as the car dives. Since the antidive forces are in the opposite directions, there is a serious resistant force to dive preventing the front suspension from moving quickly.
Aero downforce is the result of the creation of low pressure zones under the engine compar
The amount of resistance is directly related to the degree of sideview angle we put in our control arms. The left-side suspension usually is designed with about half the angle of the right side in a conventional design. For the big bar, soft spring setups, teams often introduce prodive into the left-front suspension to encourage rapid dive on entry to get the left front down quickly.
Antisquat results from the third link trying to straighten out, or become more horizontal, as the car accelerates and the rear end desires to rotate. The more third-link angle you have, the more antisquat there is. Lateral movement of the third link can change the placement of added load among the two rear tires that results from acceleration.
A small amount of pressure differential can create a lot of added "load," which increases
The very last thing you need to worry about is your aero package. I'm not saying this is not important at some level, but on short tracks, I would stress that aero downforce is overrated in most cases.
I say that with confidence because I have gone up against more aero-efficient cars with setups and body configurations that were aero-deficient and still outran them. Still, teams want the most they can get out of their cars. If all of the above nine items are in order, then go ahead with aero tweaking.
Try to understand how aero downforce is created and then configure your car so that you take advantage of every area where you could produce more downforce.
If you've been diligent in maximizing the above 10 areas of most concern, then you are well on your way to a successful season. Remember that success comes in all forms. Advancing your finishes over last season is a good step. Don't think that just your setup will lead quickly to Victory Lane. Improve your finish, learn how to win, and then, at the right moment, you'll find yourself holding the checkered flag.