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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.
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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.
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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.
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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.
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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.
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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.
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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.
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There are five things that influence the amount of traction that a set of dirt or asphalt tires will develop:
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<li> 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.
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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.
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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.
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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.
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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.
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<li>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.
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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.
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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.
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As a driver turns the steering wheel, the front tires develop an angle of attack relative to the car`s direction of travel, which increases the amount of front traction. The more the wheel is turned, the greater the angle of attack.
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If the RF tire had too much negative camber set into it, at mid-turn, the contact patch might look like this pattern, and the tire would have less traction.
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<li>Chemical Makeup - The chemical makeup of the compound of the rubber will help determine how much traction is available from a tire. A softer tire will provide more traction, but the maximum amount of traction that can be utilized over a long period of time concerns how the tire holds up to 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.
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<li>Angle of Attack - The amount of traction available from a tire can actually be enhanced by simply increasing its angle of attack relative to the direction the car is traveling, but only up to a point. From going 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 up to a point.
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There is a limit in the angle of attack that we reach where the gain in traction begins to go away. Going beyond that limiting point causes a sudden loss of grip, and traction falls off drastically. This principle is true of all four of our tires. This is a very important point to consider because it is at the very core of handling balance. We regulate our handling balance with the steering wheel within a small range of difference in front-to-rear traction.
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Some tracks and sanctioning bodies allow the use of tire treatment that changes the rubber compound. This can be a way to limit costs, allowing a team to run otherwise uncompetitive harder, older tires. Other tracks 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.
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<li>Equal Loading - An opposing pair of tires (tires on the same axle at the same end of the car) will develop maximum traction 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 in which that is not exactly true.
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That 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.
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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 needing traction. The car creates a greater amount of downforce than a flatter track due to the banking and associated lateral forces. Many times, the tires are loaded to the extent that the available horsepower cannot break the tires loose. The tracks at which we worry about increased cornering forces and increased bite getting off the corners are the ones that are flatter and have less surface grip.
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If the RF tire had too much negative camber set into it, at mid-turn, the contact patch might look like this pattern, and the tire would have less traction.
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As a driver turns the steering wheel, the front tires develop an angle of attack relative to the car`s direction of travel, which increases the amount of front traction. The more the wheel is turned, the greater the angle of attack.
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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 forward traction. A track that goes from high banking to low banking 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 weight off the left-rear tire. This causes loss of traction in that tire.
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The other problem occurs when the inside edge of the track rises to match the elevation of the outside edge of the track. As the left-front tire rises, the LF and RR pair of tires become more loaded momentarily, causing loss of loading in the opposing pair of tires. The loss of crossweight ( RF to LR ) makes the car lose traction in the rear.
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With more angle of attack, the front and gains more traction up to a point at which the angle becomes excessive and the tire loses grip and gives up most of its available traction, resulting in a severe tire push.
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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. Some older dirt tracks and ones 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 have a smaller radius than Turns 2 and 3. So its difficult to accelerate off Turn 4 due to the slower speeds caused by the decreasing radius.
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Remember, we said traction increases for a set of opposing tires when we increase the angle of attack (simply put, this is when we turn the steering wheel more). If the car is neutral in and through the middle of the turns, as we approach the tightest portion of the turn past midway, where the radius is less, we need to turn the steering wheel more; 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 into the throttle. This causes loss of rear traction. We will study ways to compensate for this later.
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We see one car can run the very bottom of the racetrack while the No. 1 car runs high. When the side bite is there the shortest way around the track is on the bottom. If we also have forward bite, we can accelerate off the corner sooner and with a more straight-ahead line.
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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 turn radii all help determine how much grip is available for traction off the corners. The setup related to shocks, springs, and rear geometry help determine how much traction will be available for a certain set of conditions.
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On asphalt tracks, and even some dirt tracks that have been oiled to the point of almost being asphalt, the surface is more consistent. Other than holes or bumps and rises in the surface, we can expect the grip to be the same over the course of the entire event. Flatter banking and older asphalt dictates the need for more traction control efforts.
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Now that we have a good understanding of exactly what affects the amount of traction in our tires, we need to examine how we can use that information to enhance the tractive properties of all four tires. In Part Two of ~Get More Bite,~ we will offer some suggestions for overcoming the problems some teams have getting enough lateral and forward bite.
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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 groomed, the back side away from the grandstand gets pushed out. This makes Turns 1 and 4 tighter than Turns 2 and 3. More steering is required for the tighter turns, and it is usually very difficult to accelerate off the corner in Turn 4 as opposed to exiting Turn 2.
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There is one traction-promoting effect that every stock car has, but few realize. It is the effect of engine torque. When we get back into the throttle, the torque from the rotation of the engine, through the driveshaft, tries to rotate the whole rear end 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 forward traction.
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A question often asked is, ~why doesn`t the car 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 effect of the engine torque. There is no way to enhance this effect, and the magnitude is entirely dependent on the amount of torque the engine develops at a given rpm versus the track width of the rear tires. The wider the rear track width, the less effect torque will have on adding to the LR weight.
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Author:ï¿½Bob Bolles
