Corvette Z06 GT3 Part 4

 Corvette Z06 GT3 Part 4

Springs and Dampers

To begin, let's introduce the concept of "static" vs "dynamic" forces.

Springs "absorb" the weight placed on each of the four wheels of the car. Stiff springs absorb this weight with less compression. Soft springs absorb this weight with more compression.  Springs are rated a Pounds per Inch.  A 1200 pound spring is compressed 1 inch when 1200 pounds is placed on it. 

From a "static" point of view, springs are selected based in part on how much compression distance is desired when the car is at rest. A weaker spring allows the wheel to move up and down more distance than a stronger spring. We will call this concept--"compliance".  A weak spring has more compliance than a strong spring. 

From a "dynamic" point of view, springs absorb energy as the car is being driven and weight is changing due to accelerating, braking, turning, impacts from bumps and dips and changes in the road surface. Weaker springs will allow the wheel/s to move more  (stronger will allow less) distance when these forces are applied. So cars with weak springs will be feel "soft" with more lean when turning and more dive/lift when braking and accelerating. Cars with heavier springs will feel "stiff".

The Corvette seems to be "happy" with 599 and 1142 springs. There are some setups using 599 and 999 but this softer rear spring is to compensate for an ultra low rear wing and high differential stiffness.

Shock absorbers don't absorb shocks. That is what springs do. Shock absorbers are more correctly called Dampers as their role is to resist and slow down the movement of the wheel. Without this damping function, springs would "yo-yo" up and down for a time. Dampers are related to the dynamic performance of the car.

Dampers work in two directions--they: 1) Resist or dampen the compression of the spring and; 2) Resist or dampen the rebound or decompression of the spring. The higher the compression setting, the more resitance to compression. The higher the rebound setting, the more resistance to decompression of the spring. 

In essence from the driver's point of view, the damper settings control the dynamic performance of the spring/damper combination. High compression and spring settings make weight transfer occur more rapidly--this can be good when wanting to change direction in a chicane for example.  This may be bad if too high as weight transfer from rear to front can make corner entry difficult as the front tires may be temporarily overloaded.

Similarly, high rebound forces also cause a more rapid weight transfer and may actually keep the tire off the ground. Lower rebound settings allow the spring to decompress more quickly keepng the tire on the ground. 

A car that is difficult to handle under braking can be "tamed" somewhat by reducing front compression damper settings and reducing rear rebound settings. This however comes with a price as the car will "dive" more and will take longer to recover.

A car that is oversteering excessively can be "tamed" somewhat by reducing the rebound on the rear dampers and increasing the compression on the front dampers. Conversely, a car that is understeering excessively can be "corrected" by the opposite-reducing front compression and increasing rear rebound.

To complicate the matter, the dampers can be adjusted for "rapid or high speed" movement and "slow" speed movement. 

So making these adjustments will require us to go back to that requirement that the driver be "hyper sensitive" to oversteer and understeer in various corners.  Damper settings can improve the handling by changing the dynamic performance of the spring/damper combination that will dramatically affect the handling. 

iRacing provides a very useful tool for analyzing this. Run a fast lap and with camera view, look at the tire's contact with the track in the corner of interest. You can actually view the tire contact patches from under the track whose size is proportional to the weight on the tire. Often, the oversteer or understeer is the result of the tire being lifted off the track momentarily. Changing damper settings can remedy the problem.

View tire contact from under the pavement

Inside rear tire is off the track in the right-hand high-speed turn

Reduce low speed rebound on rear to reduce oversteer

Do not just make changes to dampers and run a couple laps and conclude "I was faster with that change so it was good."  It takes more than a couple laps to draw conclusions. Focus more on reducing undesirabe understeer or oversteer. 

In conclusion, choosing the "correct" setup selections requires a great deal of experimentation and a very good sensitivity of the car's handling. Ultimately, there will be compromises and tradeoffs--safety vs speed. The "fastest" setup is often quite difficult to drive and hence increases the bad consequences of mistakes. We are all human and make mistakes and we are all different. Most often the setup that is slightly slower but safer wins the race.

Once you feel you have the best setup for you, drive the car for 25 laps and compare your lap times. You may choose to make more fine tuning as you progress.

I encourage you to read some of the older articles here-Setting up the Ferrari GT, Braking Dynamics, Aerodynamics and The Diving Turn.