Forces on a Banked Oval-Part 1

Understanding the forces on the four "corners" of the race car's suspension will help in the determination of the ideal spring and damper setting selection/s.

The race car on an oval experiences rapidly changing forces:  1) From the "Twist" of the banking ribbon transition between the curve and straight; 2) The rapid increase in downforce from the banking; 3) The normal "cornering force" that causes chassis roll in turns; and 4) Forces that result from deceleration and acceleration.





It is useful to think of the race car having three different "roll" axis. The first is a line drawn from front to back of the car. Lets call this the "L axis" for longitudinal. The second is a line drawn from corner to corner. Let;s call this the "X axis" for cross axis. The third is a line drawn thru the center of the car from side to side. Let's call this the "P axis" for pitch axis.

The force/s introduced by the banking transition act from corner to opposite corner about the X axis.  LF to RR; or RF to LR, etc. These forces are momentary but can be quite large and result in substantial spring compression and changes in handling. (See figure above)

The second force is produced by the extra "weight" the car experiences on all four corners because of the banking.

The third force, deemed cornering force is the centrifugal force on the center of gravity of the car that results in a reduction of weight on the inside tires and an equal increase in the weight on the outside tires about the L axis.

An analysis of suspension telemetry will show these forces as "displacements" or changes in ride height.  These changes in ride height are affected by spring choice and damper settings. The car will generally see a force about the X axis on corner entry, followed by all four corners being compressed by banking forces, while simultaneously weight is being transferred about the L axis as the car rolls in the turn. As the car exits the corner, these forces will be reduced. The weight change about the L axis from turning will return to the straight line forces. The banking compression will diminish and the car will see an opposite force about the X axis on corner exit. 

Stiffer springs will absorb less "energy" and hence, the weight transfer about the X axis, the L axis, and/or the P axis will occur faster and with a greater magnitude. Increasing the rebound damping on the shock/damper that is losing weight will cause the weight transfer to occur faster. Increasing the compression damping on the shock/damper that is gaining weight will cause the weight transfer to occur faster.

Weaker springs will absorb more "energy" and hence, the weight transfer about the X, L, and/or P axis will occur slower and with less magnitude. Decreasing rebound damping on the shock damper that is losing weight will cause the weight transfer to occur slower.Decreasing the compression damping on the shock/damper that is gaining weight will cause the weight transfer to occur more slowly. (This second set of facts can be counter-intuitive.)

The next question is usually:  How do I choose to make the car go faster?   The answer is not a universal one as the correct choice of springs and damper settings depends on the track, the conditions (e.g. track temperature and tire design) and driving line. Often the optimal choice is determined by experimental testing--starting with a base setup and making small changes to determine the changes that result in better lap times.