When your car has lots of...
When your car has lots of forward bite, it can lift the left-front tire off the ground. Here, Shannon Babb, who runs a balanced setup through the turns, powers off the corner with lots of speed.
If there is one thing we usually cannot get enough of, it is traction related to side bite and forward bite in our race cars. The bite we are talking about is what makes the tires stick while we are going through the middle of the turns and while under power off the turns and down the straightaway. Fast cars have more traction, and that traction is more balanced to make the car neutral in handling.
There has been a lot of talk over the past few years about illegal tire treatment and traction control being used in circle track racing. We know that it is being used and may have won some races, but there are better ways to legally go about developing more traction. We also know that many legal teams have been able to run faster, longer than the ones known to be using illegal means to help their tires.
Legal traction-enhancing technology has grown in recent times. We have collectively learned what the tires want and somewhat how to give them the opportunity to maintain grip with the racing surface as much as the laws of physics will allow. Let's face it-there are limits to everything in this physical world, so we go in search of the ultimate limit. We try to learn to recognize when we get to the limit so we can stop looking, lest we go backward.
The principle of stopping while you're ahead is true in developing a good handling package and remains true when developing the best traction package. Know when enough is enough. The word package is an important one, because we might well be using several different approaches at the same time to enhance traction. These rarely interfere with each other, and each one adds a little to the package. Collectively, they can add up to a marked improvement in available traction while under power.
We can see that as the number...
We can see that as the number of pounds of load the tire supports increases, the units of traction do not increase at the same linear rate. The dashed line represents an ideal linear increase in traction in relation to the increase in weight supported by the tire. That's not how it works. In reality, the solid line more closely represents the true picture. At 300 pounds of load, the units of traction are 2.4. If we double the load to 600 pounds, the units of traction only increase to 4.4 instead of double, which would be 4.8.
Let's take a look at the various areas of influence that affect the amount of traction a tire can produce and how we can maximize how our car reacts to those influences. Some are almost the same for dirt or asphalt, and some of what we discuss is very different and will be talked about separately.
Tires The tires are the ultimate connection between the car and the racing surface, as we have been told many times before. That basic principle is not a new one, but a concept that has always been at the forefront when trying to understand ways to increase handling performance in a race car. It is again at the very top of the list when we discuss traction under power.
There are five things that influence the amount of traction that a set of dirt or asphalt tires will develop:
1. Vertical Loading Increasing the amount of vertical loading (weight or downforce) on a tire increases the available traction, but in a non-linear way. That is to say that as we increase loading on a tire, it will gain traction, but not in constant multiples. If a tire has "X" amount of traction with 400 pounds of load on it, the traction will be less than double as we apply 800 pounds of loading to it. The amount of traction will be something less than 2 times X.
Vertical loading can be increased without the negative influence of added weight in the car. The use of wedged bodies, large spoilers, and softer setups has caused our cars to go faster over the past five years. Downforce is talked about in the upper levels of asphalt racing, but we see the influence has trickled down to Saturday night racing, too.
The dirt teams are paying more attention to the body shapes and working to increase negative pressure under the car, which produces valuable downforce. The asphalt teams are all over the Big Bar and Soft Spring setups that lower the car's ride height, as well as the center of gravity (CG), in the turns.
With a lower CG, less load transfers in the turns and more load is retained on the left-side tires, leading to more equally loaded sets of tires per axle. Not only is the downforce adding more load to the tires, but they are also more equally loaded and, therefore, produce more traction.
Here, we see the No. 06 car...
Here, we see the No. 06 car running loose on the bottom while the No. 3 car runs high and looks completely neutral in handling. Loss of rear traction will eventually heat the right-rear tire and make the condition worse.
As the tire pressure is reduced...
As the tire pressure is reduced from optimum, the pressure exerted on the middle portion of the tire is reduced, resulting in less traction.
The same occurs as we over-inflate...
The same occurs as we over-inflate the tire. The outer edges of the tire will lose loading on the racing surface, which results in less traction. At optimum pressure the entire width of the tire contact patch will exert equal loading on the racing surface.
If we could look down on the...
If we could look down on the tire contact patch during cornering, we would want to see an even loading pattern across the width of the tire, much like this sketch.
2. Contact Patch The size and cross-sectional loading of the contact patch helps determine how much traction we will have for a particular tire. An added benefit related to the contact patch and traction involves grooving and siping with dirt tires and will be discussed later.
Reducing air pressure will usually increase the size of the tire contact patch, or footprint, which would seem to enhance traction, but excessively low or high pressures may reduce the loading on portions of the tire so that the total pressure footprint of the tire is reduced and we end up with less available traction for that tire. There is an optimum operating air pressure for each tire that will offer maximum contact patch area with equal loading across the width of the patch.
Camber also affects the size and cross-sectional loading of the contact patch. The correct camber angle compensates for the deflection of the tire sidewalls as the lateral force is applied when we turn the car. More or less camber than what would be ideal means that one side of the tire will support more loading than the other, and this also reduces traction.