Getting the car to stick is...
Getting the car to stick is a never-ending quest in every form of ovaltrack racing.
We can never get enough traction related to forward bite in our racecars. The traction control in this case is making the tires stick whilewe are under power off the turns and down the straightaway. There hasbeen a lot of talk over the past few years about illegal tractioncontrol being used in circle track racing. We know it is being used andmay have won some races, but there may be better ways to legally goabout developing more traction under power. Many legal teams have beenable to run faster than the ones using illegal means to help keep theirtires from spinning.
Traction-enhancing technology has grown. We have collectively learnedabout what the tires want and somewhat how to give those tires theopportunity to maintain grip with the racing surface as much as the lawsof physics will allow. Let's face it. There are limits to everything inthis physical world, so we go in search of finding the ultimate limit.We try to learn to recognize when we get to that limit so we can stoplooking lest we go backwards.
The principle of stopping when you're ahead is true in developing a goodhandling package. It remains true when developing the best tractionpackage. The word "package" is an important one, because we might beusing several different approaches at the same time to enhance traction.They rarely interfere with each other and each one adds a little to thepackage. Collectively, they can add up to a marked improvement inavailable traction while under power.
We can see that as the number...
We can see that as the number of pounds of weight the tire supportsincreases, the units of traction do not increase at the same rate. Thedashed line would represent a linear equal increase in traction to theincrease in weight supported by the tire. In reality, the solid linemore closely represents the true picture. At 300 pounds of load, theunits of traction are 2.4. If we double the load to 600 pounds, theunits of traction only increase to 4.4, instead of double, which wouldbe 4.8.
In this series, we will take a look at the various areas of influencethat affect available traction and how we can maximize how our carreacts to those influences. Some are almost the same for dirt orasphalt, and some of what we discuss is very different and will betalked about separately.
(above & below) As the tire...
(above & below) As the tire pressure is reduced from optimum, the pressure on the middleportion of the tire is reduced, resulting in less traction. The sameoccurs as we overinflate the tire. The outer edges of the tire losepressure to the racing surface which results in less traction. Atoptimum pressure, the entire width of the tire contact patch will exertequal pressure on the racing surface.
Tires are the ultimate connection between the car and the racingsurface. That basic principle is not a new one, but a concept that hasalways been at the forefront when trying to understand ways to increasehandling performance in a race car. It is again at the very top of thelist when we discuss traction under power.
There are five elements that influence the amount of traction that a setof dirt or asphalt tires, the rears in this case, will develop:
1. Vertical Loading--Increasing the amount of vertical loading(weight) on a tire increases the available traction, but in a nonlinearway. As we increase loading on a tire, it will gain traction, but not inexact multiples. If a tire has "X" amount of traction with 400 pounds onit, the traction will be less than double as we apply 800 pounds ofloading to it. The amount of traction will be less than 2 times X.
2. Contact Patch--The size and cross-sectional loading of thecontact patch helps determine how much traction we will have for aparticular tire. An added area related to the contact patch and tractioninvolves grooving and siping dirt tires and will be discussed later on.
Reducing the air pressure will usually increase the size of the tirecontact patch. That would seem to enhance traction, but excessively lowor high pressures may reduce the loading on portions of the tire so thatthe total loading of the tire is reduced and we end up with lessavailable traction for that tire. There is an optimum operating airpressure for each tire that will offer maximum contact patch area andequal loading across the width of the patch.
Some tracks and sanctioning...
Some tracks and sanctioning bodies allow the use of tire treatment whichsoftens the rubber compound. This can be a way to limit cost, allowing ateam to run otherwise uncompetitive, hard, old tires. Other tracks lookthe other way on this issue and the teams must soak their tires in orderto be competitive. Promoters should define and enforce tire rules eitherway.
Camber also affects the size and cross-sectional loading of the contactpatch. The correct camber angle compensates for the deflection of thetire sidewalls as the lateral force is applied when we turn the car.More or less camber than ideal means one side of the tire will supportmore weight than the other, which also reduces traction.
3. Chemical Makeup--The chemical makeup of the compound of therubber will help to determine how much traction is available from atire. A softer tire will provide more traction, but the maximum amountof traction that can be utilized over a long period of time depends onhow the tire holds up to heat and wear. A tire that is a little hardermay sometimes hold up better and be faster towards the end of the racewhen the tires have built up a lot of heat and are well worn after anumber of laps.
(above & below) If we could...
(above & below) If we could look down on the tire contact patch during cornering, wewould want to see an even pattern across the width of the tire, muchlike the sketch on the left. If the right rear tire had too muchnegative camber set into it, at mid-turn, the contact patch might welllook like the pattern on the right and the tire would have lesstraction.
4. Angle of Attack--The amount of traction available from a tirecan actually be enhanced simply by increasing its angle of attackrelative to the direction of the car, but only up to a point. Fromstraight ahead, we can turn the wheel and, with each degree of angle ofdeviation from the direction of travel, the traction in the tireincreases. There is a point we reach where the gain is reduced and weapproach the limit of attack angle that the tire can handle. Once thatpoint is reached, going beyond causes a sudden loss of grip and tractionfalls off drastically. This principle is true of all four tires whetherfront or rear. We will provide more on this subject later.
5. Equal Loading--An opposing pair of tires (tires on the sameaxle at the same end of the car) will develop maximum traction when theyare equally loaded. That is a generally true statement, but upon morecareful examination of how we do things in circle track racing, there isa unique situation where that is not exactly true.
The situation is when we have a tire on one side of the car (usually theleft side) that is built with a softer compound than the opposing tirewhereby it may be able to develop more grip under the same loading asthe opposing tire. So, increasing the vertical load on the inside tirewith the goal of attaining equal loading for both tires, by whatevermeans, may not actually generate more traction because of the differencein grip per pound of vertical loading created by differences incompounds.
The shape of the track for both dirt and asphalt can influence theavailable traction in several different ways. As we apply power, we needto know a little about how the track is banked, how the banking angle ischanging coming off the corners, and how the radius of the turn might bechanging. A highly-banked racetrack is very forgiving when it comes toneeding bite off the corners. There is so much downforce due to thebanking and associated lateral forces, that many times the tires areloaded to the extent that the available amount of horsepower cannotbreak the tires loose under normal conditions with a balanced setup. Thetracks we often worry about getting off the corners are the ones thatare flatter and with less surface grip.
Many current dirt tracks,...
Many current dirt tracks, as well as some asphalt tracks that used to bedirt, have developed a "D" shape. This is caused by having a wall alongthe grandstand side only. As the track gets raced on and groomed, theback side away from the grandstands gets pushed out. This makes Turns 1and 4 tighter than Turns 2 and 3. More steering is required for thetighter turns and in Turn 4 it is usually very difficult to get tractionunder power, as opposed to exiting Turn 2.
The severity of change in banking angle of the racing surface in theportion of the track where we are initially accelerating can causechanges to the pitch angle of the chassis that works to unload one ormore tires, reducing traction. A track that goes from high banking tolow banking fairly quickly can cause the left rear tire to unloadquickly, making the car loose.
There are two ways this can happen. One is when the outside edge of thetrack drops in elevation and the right front tire follows the drop-off.This lifts weight off the left rear tire, causing loss of traction inthat tire.
The other problem occurs when the inside edge of the track rises up tomatch the elevation of the outside edge of the track. As the left fronttire rises up, the left front and right rear pair of tires become moreloaded, momentarily causing loss of loading in the opposing pair oftires. The loss of crossweight percent (right front to left rear) makesthe car lose traction in the rear.
A track that has a decreasing radius in the latter portion of one of theturns can cause a car to develop a loose condition at that point.Usually, older tracks that were originally dirt and then paved retain astraight 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 forthat reason. So, it is difficult to accelerate from Turn 4 because ofthe decreasing radius.
(above & below left) As a...
(above & below left) As a driver turns the steering wheel, the front tires develop an angleof attack relative to the direction of travel of the car. The more thewheel is turned, the greater the angle of attack. With more angle ofattack, the front end gains traction up to a point where the anglebecomes excessive and the tire gives up most of its available traction,resulting in a severe push.
Remember, we said traction increases for a set of opposing tires when weincrease the angle of attack (simply put, this is when we turn thesteering wheel more). If the car is neutral in and through the middle ofthe turns, then as we approach the tightest portion of the turn pastmidway, where the radius is less, we need to turn the steering wheelmore and that produces more front traction than rear traction. Thebalance we enjoyed through the middle of the turn is now upset and thecar becomes loose just when we are getting back in the throttle. Thiscauses loss of rear traction. We will study ways to compensate for thislater.
The surface largely determines the amount of traction available underpower and we will look at dirt and asphalt tracks separately. On dirttracks, the amount of moisture dictates the amount of grip the trackgives us. Bumps, grooves, banking angles, and the overall radius allhelp determine how much grip is available for traction off the corners.The setup related to shocks, springs, and rear geometry help determinehow much traction will be available for a certain set of conditions.
On asphalt tracks, and even some "dirt" tracks that have been oiled tothe point of almost being asphalt, the surface is more consistent. Otherthan holes or bumps and rises in the surface, we can expect the grip tobe the same over the course of the event. Flatter banking and olderasphalt dictates the need for more traction control efforts.
Now that we have some kind of understanding of just what affectstraction in the rear tires, we need to examine how we can use thatinformation to enhance the tractive properties of the rear set of tires.Next month, we offer some suspension tuning suggestions for overcomingthe problems some teams have getting enough bite off the corners.
Engine Torque Promotes Equal Loading
Engine torque is one effect every stock car has that promotes traction.When we get back in the throttle, the torque from the rotation of theengine, through the driveshaft, tries to rotate the whole rear end in acounter-clockwise direction when viewed from the rear. This action, orforce, loads the left rear tire as well as the right front. When thosetwo corners are more loaded, the crossweight percent goes up and the cargets tighter. Also, if the right rear tire was supporting more weightthan the left rear tire, then with this effect, the two rear tires wouldbe more equally loaded and providing more traction.
A question often asked is why the car does not get loose immediatelywhen we gas it up if the rear tires are already providing all of theiravailable traction to keep the car off the wall. The introduction ofpower would cause the tires to lose traction if it were not for theadded effect of the engine torque. There is no way to enhance thiseffect and the magnitude is dependent on the amount of torque the enginedevelops at a given rpm versus the width of the rear tires. The widerthe rear track width, the less effect torque will have on adding to theleft rear weight.