If the moment center is moved to the right, the front suspension of the car tends to get stiffer, much like increasing the spring rates. A location that is more to the left makes the front end softer and helps the car turn better.
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 left will help tighten the car. If overdone, the car will push.
1. Front-End Geometry
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 with a laser system or with strings. A very small amount of Ackermann can be desirable on smaller, shorter tracks. A quarter of a degree is as much as will ever be needed.
2. Rear Geometry
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.
3. Steering Geometry
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.