The single most sought after goal for all racers is the pursuit of increased traction for added speed in the turns and for better forward bite. The "traction control" spoken of here is about making the tires grip better while going through the turns and while under power off the turns and down the straightaway. We will provide some valuable information about how tires gain traction and then how we can design our cars so that we take advantage of that knowledge.
There's been a lot of talk over the past few years about illegal traction control being used in circle-track racing. We know that it's been used and may have helped win some races, but there may be better ways to legally go about developing more traction, especially while under power. We know that many legal teams have been able to run faster than the ones known to be using illegal means.
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 our goal is to find the achievable limits. We need to learn to recognize when we get to that limit so we can stop looking, lest we go backwards.
If traction increased at the...
If traction increased at the same rate as loading, we would see a result indicated by the dashed line. It doesn't, so we see, as shown by the solid line, that as the number of pounds of loading on the tire increases, the units of traction do not increase at the same rate. 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.
The principle of stopping when 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. They rarely interfere with each other and each one will add a little to the package. Collectively, they can add up to a marked improvement in available traction.
In this two-part series, we will take a look at the various areas of influence that affect available traction 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. Let's begin our lesson.
Tires, as most race car engineering books will tell you, are the ultimate connection between the car and the racing surface. That basic principle is a concept that has always been at the forefront when trying to understand ways to increase handling performance in a race car. It's also at the very top of the list when we discuss traction under power. There are five basic effects that influence the amount of traction that a set of race tires will develop:
1. Vertical Loading
Increasing the amount of vertical loading on a tire increases the available traction, but in a non-linear way. This loading can be the result of static weight increase, lateral load transfer, or aero downforce. As we increase the loading on a tire, it will gain traction, but not in an amount equal to the percent of increase in load. If a tire has "X" amount of grip with 400 pounds of load on it, the grip will be less than double if we apply double the loading of 800 pounds to it. The amount of traction will be somewhat less than twice X.
2. Contact Patch
The size and cross-sectional loading of the contact patch helps determine how much grip we will have for a particular tire. An added effect related to the contact patch and traction involves grooving and siping with dirt tires and will be discussed later.
Reducing the air pressure will usually increase the size of the tire contract patch 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 grip 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 and equal loading across the width of the patch.
When we put asphalt tires...
When we put asphalt tires on a Dirt Late Model, we need to be more aware of tire pressures and cambers. Dirt is a medium that is more forgiving for many settings, including camber, pressure, toe, rear steer, and Ackermann.
Always check your cambers...
Always check your cambers and when you find the correct setting that will produce the optimum heat across the tread and even wear, maintain those cambers. For different conditions you might need to reset the cambers. For tight and wet tracks on dirt, more camber is required than for dry slick track conditions.
As the tire pressure is reduced...
As the tire pressure is reduced from optimum, the pressure on the middle portion of the tire is reduced resulting in less overall grip. We may see more contact patch area, but less equal loading.
The same occurs as we over-inflate...
The same occurs as we over-inflate the tire. The outer edges of the tire loose pressure to the racing surface which results in less traction. At optimum pressure, the entire width of the tire contact patch will exert equal pressure on the racing surface.
If we could look down on the...
If we could look down on the tire contract patch during cornering, we would want to see an even pattern across the width of the tire as shown.
If the tire had too much negative...
If the tire had too much negative camber set into it, at mid-turn, the contract patch might well look like this pattern and the tire would have less overall grip.
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 load than the other and this also reduces traction.
Some tracks and sanctioning...
Some tracks and sanctioning bodies allow the use of tire treatment which softens the rubber compound. This can be a way to limit cost allowing a team to run otherwise uncompetitive hard, old tires. Other tracks outlaw tire soaking but look the other way on this issue and the teams must soak their tires in order to be competitive. Promoters should define and enforce tire rules either way.
3. Chemical makeup
The chemical makeup of the compound of the rubber will help to determine how much traction is available from a tire. A softer tire will provide more grip, but the maximum amount of traction that can be utilized over a long period of time concerns how the tire holds up to increased heat and wear. A tire that is a little harder may sometimes hold up better and be faster toward the end of the race when the tires have built up a lot of heat and are well worn after a number of laps.
4. Angle of attack
The amount of traction available from a tire can actually be enhanced simply by increasing its angle of attack relative to the direction the car is traveling, but only up to a point. From traveling straight ahead, we can turn the wheel and with each degree of angle of deviation from the direction of travel, the traction in the tire increases.
There is a point we reach where the gain is reduced and we approach the limit of the attack angle that the tire can handle. Once that point is reached, going beyond causes a sudden loss of grip and traction falls off drastically. This principle is true of all four of our tires whether they are the front or rear tires. We will provide more on this subject later.
5. Equal loading
An opposing pair of tires (tires on the same axle or at the same end of the car) will develop maximum grip when they are equally loaded. That is a generally true statement that has been made many times in the past in countless publications. Upon more careful examination of how we do things in circle track racing, there is a unique situation where that is not exactly true.
The situation is when we have a tire on one side of the car (usually the left side) that is built with a softer compound than the opposing tire whereby it may be able to develop more grip under the same loading as the opposing tire. So, increasing the vertical load on the inside tire with the goal of attaining equal loading for both tires, by whatever means, may not actually generate more traction because of the difference in grip per pound of vertical loading created by differences in compounds.
The shape of the track for both dirt and asphalt can influence the available traction in several different ways. As we apply power, we need to know a little about how the track is banked, how the banking angle is changing coming off the corners and how the radius of the turn might be changing.
A highly banked racetrack is very forgiving when it comes to the need for bite off the corners. There's so much downforce due to the banking and associated lateral forces, that many times the tires are loaded to the extent that the power generated by the motor can't break the tires loose. The tracks we are most concerned about getting off the corners are the ones that are flatter and with less surface grip.
The severity of change in banking angle of the racing surface in the portion of the track where we are initially accelerating can cause changes to the pitch angle of the chassis that works to unload one or more tires which can reduce traction. A track that goes from high banking in the turns to low banking on the straights fairly quickly can cause the left rear tire to unload quickly making the car loose. There are two ways this can happen. One is when the outside edge of the track drops in elevation and the right front tire follows the drop-off which, in-turn, lifts load off of the left rear tire causing loss of traction in that tire.
As a driver turns the steering...
As a driver turns the steering wheel, the front tires develop an angle of attack relative to the direction of travel of the car. The more the wheel is turned, the greater the angle of attack.
With increased angle of attack,...
With increased angle of attack, the front end gains traction up to a point where the angle becomes excessive and the tire gives up most of its available traction resulting in a severe push. We use this effect to overcome a tight car. A severely tight car is termed "tight-loose" and the excess steering input results in the car becoming loose past the mid-point of the turn.
Many current dirt tracks as...
Many current dirt tracks as well as some asphalt tracks that used to be dirt have developed a "D" shape. This is caused by having a wall along the grandstand side only and as the track gets raced on and graded, the back side away from the grandstands gets pushed out. This makes the radii of Turns 1 and 4 smaller and tighter than Turns 2 and 3. More steering is required for the tighter turns and in Turn 4, it's usually very difficult to get traction under power as opposed to exiting Turn 2.
The other problem occurs when the inside edge of the track rises up to match the elevation of the outside edge of the track. As the left front tire rises up, the LF and RR tires become more loaded momentarily causing loss of loading in the opposing pair of tires. The loss of crossweight percent (RF to LR) makes the car lose traction in the rear.
A track that has a decreasing radius in the latter portion of one of the turns can cause a car to develop a loose condition at that point. Usually, older tracks that were originally dirt and then paved retain a straight front stretch and a rounded out back "straightaway." This "D" shape causes Turns 1 and 4 to be a smaller radius than Turns 2 and 3 for that reason. So, Turn 4 is difficult to accelerate off of due to the decreasing radius.
Remember we said that traction increases for a set of opposing tires when we increase the angle of attack as we turn the steering wheel. If the car is neutral in and through the middle of the turns, then as we approach the tightest portion of the turn past midway, where the radius is the least, we need to turn the steering wheel more, and that produces more front traction than rear traction. The balance we enjoyed through the middle of the turn is now upset and the car becomes loose just when we are getting back on the throttle. This causes loss of rear traction. We will study ways to compensate for this later.
The Racing Surface
The surface we race on largely determines the amount of traction available under power and we will look at dirt and asphalt tracks separately. On dirt tracks, the amount of moisture dictates the amount of grip the track gives us. Bumps, grooves, banking angles, and the overall radius all help determine how much grip is available for traction in and off the corners. The setup related to cambers, shocks, springs and rear geometry help determine how much traction will be available for a certain set of conditions.
On asphalt tracks, and even some dirt tracks that have been oiled to the point of almost being asphalt, the surface is more consistent and, other than holes or bumps and rises in the surface, we can expect the grip to be the same over the course of the event. Flatter banking and older asphalt dictates the need for more traction control efforts.
Now that we have some kind of understanding of just what affects traction in the rear tires, we need to examine how we can use that information to enhance the tractive properties of the rear set of tires. In Part Two of Legal Traction Control coming in next months issue of CT, we will offer some suggestions for overcoming the problems some teams have getting enough bite.
Engine Torque Promotes Equal LoadingThere is one effect that helps promote traction that every stock car has, but few realize, and that is the effect of engine torque. When we get back on the throttle, the torque from the rotation of the engine, through the driveshaft, tries to rotate the whole rearend in a counter clockwise direction when viewed from the rear. This action, or force, loads the left rear tire as well as the right front. When those two corners are more loaded, the crossweight percent goes up and the car gets tighter. Also, if the RR tire was supporting more weight than the LR tire, then with this effect, the two rear tires would be more equally loaded providing more traction.
A question often asked is why the car does not get loose immediately when we gas it up if the rear tires are already providing all of their available traction keeping the car off the wall. The introduction of power would cause the tires to lose traction if it were not for the added affect of the engine torque. There's no way to enhance this effect and the magnitude is dependant on the amount of torque the engine develops at a given rpm verses the width of the rear tires. The wider the rear track width, the less effect torque will have on adding load to the LR tire.