(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 Racing Surface
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.