One of the characteristics of a good driver is that he or she is able to use the potential of his vehicle to the maximum in a safe manner. Whatever the type of vehicle, the foundation of being able to use all of the performance available is to use the friction between the tires and the road surface as best as possible. With a tire at each corner, the contact patch of each is usually about the size of a book, and all forces generated during the course of driving must be transmitted through these patches.
The first thing to consider is tire pressure. For a given tire and load, the ideal tire pressure is the one that does not distort the structure of the tire and keeps the entire tread surface in contact with the road surface. Keeping load the same, too much pressure will lift off the edges of the tread from the road surface since the tire will bulge out, and too low a pressure will lift up the center of the tread from the road surface. This effect will be more on a wider tire than on a narrow tire, both with the same contact patch area.
The next things to consider are the softness/hardness of the rubber compound and the type of tread pattern. Soft rubber will increase the grip since the tire will conform more easily to all the irregularities of the road surface, but will also wear out quicker. For all ranges of hardness, increased temperature will increase grip up to the melting point of the rubber compound. The amount of rubber in contact with the road is also determined by the “void ratio” of the tread pattern. For example, a racing slick tire has a void ratio of 0%, whereas a tire with 10 inches of tread width with five grooves, each an inch wide, will have a void ratio of 50%.
Now we can consider the actual forces that will act through each tire: acceleration, braking, and turning left or right. Each contact patch will have a total amount of force that it can generate by friction with its pressure, rubber hardness, and tread pattern that it can allocate to all of these activities. It is up to the driver to determine how he or she wishes to distribute force available to each of these forces.
The sum of these demands on the total force available cannot exceed the total grip provided by the contact patch. Think of it as a fixed budget available at each corner. The driver can spend all of it on braking, but then he/she has nothing left over for turning. If he/she wants to use some of the budget for accelerating out of a turn, then the amount available to provide cornering force has to be reduced.
With these concepts, we can now see how proper driving technique distributes the “budget” allocation at each corner while driving. When driving at a leisurely pace, the reserves available are so large in comparison to the demands being made that it does not really matter. However, when the pace is quickened, proper allocation becomes more and more important, and driving right at the edge of the performance envelope, it can make all the difference between winning and loosing on a track, or even life and death in an emergency situation on the road.
Let’s consider a car being driven briskly on a twisty mountain road, with curves and gradients. As the car enters a curve at speed, more and more of the force needs to be allocated to turn, so the braking to a safe speed must be done before the sharpest part of the curve comes up. As the car enters the turns, no further braking is required, and some of the allocation can be diverted to accelerating the car out of the turn. The driver also has to consider the effect of sudden rises and drops, since the weight of the car on each corner will change and thus change the amount of force available to be allocated. Obviously, a tire up in the air cannot provide any force at all, so while being airborne may make for exciting photography, it is not conducive to the health of the driver or his/her passengers.
The type of suspension and its compliance also play their role while the car goes around the curve. Suspension geometry will determine how parallel the tire will remain to the road as the car leans. Suspension compliance will determine how far the car leans, and transfer weight to the outside wheels, and the overall weight balance of the car at each corner. In certain situations, it is not unusual for one inside wheel to lift off the road surface altogether.
It is important to remember that all of the above happens very quickly, and is dynamically changing all the time. Therefore, the driver cannot afford to be inattentive for even a fraction of a second. When driving at the limit, there is no margin for error. After attention, the next most important thing is smoothness. A good driver will manage all these transitions in a smooth manner, with no sudden jerks between transitions of forces. Of course, if the road surface is broken, bumpy and potholed, it becomes very difficult, since the transitions become unpredictable. Recovery from sudden unplanned changes if any corner of the car catches a bump mid-corner often takes quick reflexes.
Add to this mix a little bit of weather related conditions like rain or snow, time of day related conditions like fog or darkness, and then throw in the spice of other drivers on the road traveling at various rates of speed, and one can see why driving in Pakistan can be a true challenge. However, if PakWheels is any guide, there are plenty of drivers who have mastered the art of skillful driving in Pakistan. This article is dedicated to these heroes!