WEIGHT TRANSFER, CG, TRACK AND WHEELBASE
We talked about weight transfer earlier, let's go back to it for a moment. As we discovered, the weight of the car pushing down on the tires will make them grip better. At one point, they have too much download on them so they 'let go' and begin to slip.
Three factors determine the amount of download you put on tires: the cars wheelbase, track and its center of gravity. Without going into the details of why, a car can attain higher levels of lateral acceleration when the CG is lower to the ground and the wheelbase and track is wider. All else being equal a tall, skinny car with a short wheelbase will overload its tires before a low, wide car with a long wheelbase. This is why F1 cars are so low and wide, and the tires are pushed out to the far corners.
Obviously, at least two of these factors are out of your control in GT3, but we can talk about one that is: CG. You can change the ride height of any car with Full Race suspension. There's a simple principle here: go as low as you can, until the car begins to bottom out.
SO WHY DO WE HAVE SUSPENSIONS?
Reason one: bumps. If the world was as smooth as a billiard ball table, we could probably mount the wheel to a solid beam that bolts right to the car's frame. But a car with such a stiff suspension would knock its driver and itself senseless in the real world. The real problem is that if the car encounters a bump while cornering, it would bounce and go airborne -- this sudden reduction in download would do truly terrible things to a car's handling and probably send it right off the road.
The second reason why suspensions exist is to help distribute download across all the tires. We can't change the amount of weight transfer when a car corners, but we can change where it goes and how quickly. To a degree.
So the suspension in a race car has two goals: 1) to ensure the amount of tire download does not change dramatically when the car encounters a bump, and 2) to ensure the best possible distribution of that download across the available tires.
There are 3 basic factors in your suspension that help you achieve these goals. The Spring Rate, Damper Stiffness and Stabilizer Stiffness.
SPRING RATE
We all know what springs are and what they do. Lets change our thinking about them slightly. Each spring holds a certain portion of the cars total weight. Thus, if we change the stiffness of the springs, we can change (to a degree) how much weight is distributed to each tire when the car corners.
As a general rule, you want to set your car to run with the highest spring rates that the course will permit. The reason is that high spring rates will allow you to set the ride height low while reducing the possibility of bottoming out. As we discovered earlier, the lower, the better. As you encounter bumps or the rumble strips (sometimes called aprons), too firm a spring rate may cause the car to lose download.
You can also use spring rates to trim car balance, which we'll talk about in the next section.
DAMPER (Shocks)
A shock absorber or damper resists motion. If you've ever held one, you may notice its not too hard to compress , but it is very hard to compress it quickly. The same is true when a shock absorber extends.
When a car hits a bump, the spring absorbs the shock of the bump instead of transmitting it to the rest of the car. After the initial impact, the spring will extend to its original height with a similar amount of force. If this force is not contained and controlled, a car that hits a bump will continue to bounce several times, losing a little energy each time. Clearly this will do bad things to the amount of download on our tires, so we have a shock absorber that is designed to let the car absorb the initial impact of a bump, then re-extend to its original height just once. The shock absorbs the excess energy contained within the spring. Thus, the shocks have a supporting role with the springs and should be thought of as a supplement to good spring rates.
As a general rule, the stiffer your spring rates, the higher your shock stiffness should be. It is very important to match the amount of shock stiffness with your spring rate. Too stiff and your car will be jittery over bumps. Too soft and your car will oscillate after bumps.
You can also use shocks to augment spring rates in trimming car balance, which we'll talk about in the next section.
STABILIZER (Sway-bar, or anti-roll bar)
A sway bar is a simple torsion bar that transfers download laterally. During cornering, a certain portion of the download on the outside of the car is transferred to the inside of the car. The stiffer the bar, a greater portion of download is transferred. This ensures that the inside tires are retaining some amount of download so as not to overload the outside ones.
As a general rule, you should use a sway-bar to eliminate excess body roll that the springs do not eliminate, or to trim car balance, which we'll talk about in the next section.
Avoid over-reliance on sway-bars. Too stiff a bar will hurt you in the long run because you are in effect linking two sides of the car together, thus, making your suspension LESS independent.
In the next post, we'll talk about triming car balance with these suspension parts.