It's been three years since we discussed the subject of handling fixes. In that time, a lot has changed with how racers on asphalt set up their cars. So, with some of the information we have learned over those years applied, here is a modernized version of that article. The basics remain the same, but with a few critical adjustments.
Good handling has often been thought of as a car that is neutral as it runs through the entry, middle, and exit phases of the corner. That is fine as a goal, but what we really want is both balanced and neutral. The setup that will stay consistent throughout the race is the one that wins, and balance provides that consistency.
We should divide the turn...
We should divide the turn into three phases or segments in order to analyze the handling. The middle phase is most important to overall track performance. Entry and exit performance helps us pass cars on the racetrack.
Here is a recent quote from a reader who has found that perfect balance. "In the 50-lap Main, our fastest lap time was clocked on Lap 43. We were 0.13 faster than we qualified. The chassis was as good or better at the end than it was at the beginning."
When the car is not balanced, the neutral handling does not stay with the car for very long. An unbalanced car can be very fast, although the thrill lasts but for a short time. So testing for the fastest lap does not guarantee success. Here, we will examine the problems associated with a car that handles poorly and some logical steps to take to find the most 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). The wine-and-cheese crowd refers to these as oversteer and understeer. Let's stay with the circle track lingo. The tight or loose condition can exist in one or more of the three phases of a turn (entry, middle, and exit). The cure must address where the car is not handling and ideally not affect those areas where the car is good.
The moment center (sometimes...
The moment center (sometimes called the roll center) location is very important in determining how efficient the front end will be. It helps the car turn and provides balance for the overall setup.
We will look at each phase of the corner and offer handling remedies based on the phase they affect. We should start with the mid-turn handling because problems that affect the car in the middle can also affect the entry and exit. If we can get the car to handle well in the middle, then we might have already solved some of the entry and exit problems, too. Usually, improved mid-turn handling offers the most gain in overall performance, and that is why we start there. We also want to make sure that adjustments to other segments later on do not affect the mid-turn handling.
Mid-turn handling problems are caused by a car that is either tight or loose. By far the most common handling malady historically is inability to turn. This can be caused by several different conditions, or a combination of those. We will need to go through a checklist to eliminate some familiar problems. The following is a list of things that can make the car not want to turn or make the car loose.
The amount of Ackermann in...
The amount of Ackermann in our rack-and-pinion steering system can be regulated by moving the rack forward or backward in the car. This adjusts the top-view angles of the tie rods to change the amount of spread that occurs between the ends of the steering arms as we steer the car. This is a great way to adjust Ackermann for dirt cars, where steering is in both directions.
The front moment center (MC) location plays a huge role in how the front end wants to work. The MC should always be somewhere close to the centerline (i.e., midway between the tire contact patches). The farther left the MC is located, the more efficient the front end will be and will want to roll. The farther to the right of the centerline, the less the front end will want to roll. Low-banked tracks require a location more to the left and higher banked tracks are best set up with a MC more to the right of centerline.
The center of gravity (CG) height influences where the MC should be located. Cars with a lower CG should have a MC that ends up farther to the left side of the scale than would cars with a higher CG.
In the front-end geometry, there is a condition called Ackermann. This is an effect that increases the amount of toe-out in our race cars when we turn the steering wheel.
The opposite of Ackermann is called reverse Ackermann. That is an effect that causes a decrease in the amount of toe-out as we steer 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.
We can change the amount of...
We can change the amount of Ackermann in our drag link steering system in a way similar to how we adjust the rack-and-pinion system. If we move the drag link forward in the car, we will take top-view angle out of the tie rods and reduce the amount of Ackermann in this system.
With excess Ackermann designed into our cars, on purpose or not, we can gain a lot of toe-out, which causes our front tires to work against each other. When this is severe, the front end will push and no adjustment to other setup parameters will seem to help the situation. When running balanced setups that work the left-front tire, we must eliminate most of the Ackermann.
In the common asphalt setups of today, where we use a larger sway bar and softer springs (BBSS), the presence of Ackermann effect could be more detrimental. As we use the left-front tire more and more, the negative results of Ackermann become more apparent.
If the rear end is not aligned properly, the car may be either tight or loose in all three phases of the turns. One of the very first tasks in setting up a race car is to make sure all of the alignment issues have been corrected. The rear end should be at right angles to the chassis centerline, and the right side tire contact patches should be inline.