In years past, a fast race car was considered one that was neutral in handling. Neutral is definitely a goal, but we have learned more about what makes a race car capable of winning. What we really need is a car that is neutral and dynamically balanced that will stay consistent throughout the race. If you have listened to Nextel Cup or Formula 1 racing, you have heard the teams speak in terms of the balance of the setup. This is what they are talking about.
When the car is not neutral, there are both good and not-so-good ways to make it neutral. Here, we will examine the problems associated with a poor-handling race car and some logical changes to create a more-balanced setup.
A poor-handling car is defined as one that is either loose (rear has less traction than the front) or tight (front has less traction than the rear), or what the "left-and-right" racers refer to as "oversteer" and "understeer." These conditions can occur in any of the three phases of the turns, entry, middle, or exit, or any mix of the three. The cure must address the phase where the car is not handling, while ideally, not taking away from the areas where the car is working well.
Dividing the turn into three...
Dividing the turn into three phases or segments helps us concentrate on the way the car handles in each phase.
Let's take a look at each phase of the corner and present handling solutions based on what the car is doing at each point. We will start with midturn handling because the problems that affect the car in the middle can also affect entry and exit performance.
If we can get the car to be balanced in the middle, then we might solve some of the entry and exit problems, too. Usually, improved midturn handling offers the most gain in overall track performance, and that is why we start there and then make sure that segment remains good as we make changes to improve the other two phases.
Midturn HandlingMost midturn handling problems have been related to cars that do not turn very well. With the advent of new big bar and soft spring (BBSS) setups on asphalt, that trend has reversed so that the more common problem with BBSS setups is that the car is loose in the middle.
By far the most common handling problem across the industry is a car that will not turn. This can be caused by certain individual conditions or a combination of several. We can go through a checklist to eliminate some familiar problems. The following, in order of significance, is a checklist of things that can prevent the front end from turning.
These two cars exhibit very...
These two cars exhibit very different attitudes, which leads us to think they have entirely different setups in their cars.
1. Front Moment Center Location As has been stated many times before, the front moment center location plays a huge role in how efficient the front end will be. The MC should always be located in close proximity to the centerline that is established as the midway point between the tire contact patches.
The farther left the MC is located, the more efficient the front end will be, and the car will feel like it has softer springs. The farther to the right of the centerline, the less efficient the front end will be, feeling somewhat hard-just like running very stiff springs. Cars running on lower-banked tracks require a location more to the left, and cars running on higher-banked tracks are best designed with an MC more to the right of centerline.
The center-of-gravity (CG) height also influences where the MC should be located. Cars with a lower CG can have an MC design that is located farther to the left than that of cars with a higher CG.
2. Excess Ackermann In the realm of front-end geometry, there is a condition called Ackermann. This is an effect that is part of the design of the steering system. If Ackermann effect is present, there is an increase in the amount of toe-out when we turn the steering wheel. The Ackermann effect can happen only when the wheels are turned left or when turned both directions.
The moment center (what used...
The moment center (what used to be called the roll center) location is very important in determining how efficient the front end will be, and a proper design helps the car turn and provides a more balanced overall setup.
The opposite of the Ackermann effect is called reverse Ackermann. This is a designed-in effect that causes a loss in the amount of toe and can actually cause the front tires to end up with toe-in if the effect is severe. It is possible to have Ackermann in our steering system when we steer left and reverse Ackermann when we steer to the right.
With Ackermann designed into our cars, whether deliberate or not, we can gain a lot of toe-out, which causes the front tires to scrub and lose traction. With excess Ackermann, the front end will push and no adjustment to other setup parameters will help the situation. We must eliminate most of the Ackermann in our steering systems. The solution is different for the two most common types of steering systems we find in circle track stock cars.
In the rack-and-pinion steering system, if we have equal-length steering arms and still have excess Ackermann, we need to reduce the top-view angle of the tie rods. We do this by moving and mounting the rack more forward. As we take the top-view angle out of the tie rods and make them more perpendicular to the centerline of the car, we reduce the amount of "spread" that occurs as we turn the steering wheel, and the outer tie-rod pivots move rearward through the arc created by the steering arms.