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.