Garage Storage Organization and Garage Cabinets

2TONE_93GT · 12-30-2005, 03:58 PM

taken from another site...

Quote:

Here is how I learned to think about launching a car. Imagine pushing on a refrigerator on a tile floor. Your feet are representing the tires on your car. The Center of Gravity (CG) of the refrigerator is imagined to be in the very MIDDLE on one of the shelves. If you were to push on the refrigerator somewhere above the CG then you will probably push it over (the refrigerator won't move) and you won't feel much pressure on your feet. Now, if you push on the refrigerator 2" from the ground, you will slip on the ground (not getting traction) and the refrigerator won't move. If you push on one side of it then it will turn and not go straight.

But somewhere in between the CG and the ground will be the "sweet spot" where you will get the most traction and the refrigerator will move the easiest. When changing the suspension, what you are looking for is the Least amount of power to move the car the quickest. This is Efficiency.

Definitions:

Center of Gravity (CG):

Imagine the weight of your car concentrated in an area the size of your fist and located on top of your shifter handle. The actual position will need to be calculated but this is just for a visual aid.

Instant Center (IC):

Ladder Bar- The IC is the front ladder bar mounting hole.

Four-Link- The upper and lower bars are angled toward each other. The IC is the imaginary point of intersection if you were to draw a line along the length of the lower and upper control arms forward.

Percentage of Rise (PR):
Imagine a line drawn down to the ground from the CG (your shifter handle). Now draw a line forward from the contact patch of the rear tire through the line from the CG (the line should be drawn so it is below the CG). This intersection is the PR.

See Graph (attachment #1)

Getting back to the CG. Let's say the CG is 26" above the ground, sitting on top of your shifter handle. This 26" is represented as 100% and 13" (halfway up from the floor) is represented as 50%.

When you found the PR (when you drew the imaginary line from the contact patch through the vertical line from the CG) it intersected it at, let's say 18" from the ground. Then the suspension is said to have a PR of 69% (18" / 26" = 69 or 69%). Generally, cars equipped with automatic transmissions need a PR greater than 50%. Cars equipped with manual transmissions need a PR less than 50%.

The HIGHER the PR the HARDER the suspension Hits the tires. The LOWER the PR the SOFTER the suspension Hits the tires.
Manual transmission cars already hit the tires plenty hard when the clutch is dropped so need very little PR compared to an automatic equipped car. By comparison, automatic cars (no T-brake) don't hit the tires hard at all.
See Anti Squat for another term used for describing how to set up a chassis.

Shocks

The goal of the front shocks is to control the rise and fall of the front end. The most efficient launch is when the front end rises slowly and settles down slowly while the car is still accelerating. The rate that the shocks extend and collapse is dependent on many factors: Tire size, rear gear ratio, first gear ratio, T-brake, torque converter stall, vehicle weight, horsepower, track conditions, etc.
If you were to graph the front bumper during a launch you want a nice even rise and a nice even fall throughout the first 20-60 feet. You don't want the bumper to pop up quickly then fall slowly. you also don't want the bumper to pop up quickly then fall quickly.

Fact: Maximum weight transfer occurs when the front shocks are at Maximum extension.

If the front end is soft and rises easily then maximum weight transfer happens within the first 2 feet of the launch. Once the shocks are fully extended, the only direction they can go is back down. Once the shocks start collapsing, the rear tires start to unload. What can happen is that the front end will rise quickly and get traction but then the front end starts to settle. With a car that produces a lot of power this will cause the car to hook hard initially for the first 3-5 feet then start to spin the tires while the shocks are collapsing from full extension. If the car does not have enough power to spin the tires then the car just wasted energy on raising the front end instead of pushing the car forward.

*Remember: It's not about getting traction. It's about launching the car Efficiently.*

If the front end is soft and takes little effort to lift the front bumper then the very first reaction during a launch is for the front end to rise instead of the car to move forward. I prefer to have the front end rise as slowly as possible. This means that any available energy is directed toward making the car move forward instead of up. If the car is moving up, then it is not moving forward which slows down the 60' time. There can be a fine line where the front end does not rise quick enough and can slow down the 60' times because it is working the engine too hard and doesn't allow the engine to rev quick enough. This is where adjustable shocks help.

Here is an example that will help explain how the front shocks and the rear tires react to each other.
Imagine standing on a bathroom scale and holding one end of a 12 foot long board. The other end is being supported by a friend. Your feet represent the rear tires and your friend represents the front springs/shocks.

-Try lifting the board out of your friends hands from your end of the board. With no help from your friend the board will feel very heavy and as you try to lift the board, you will apply pressure to the bathroom scale. This is similar to the reaction that the tires will feel with stiff rebounding front shocks.

-Now do the same thing but allow your friend to help lift the board. As your friend is helping, the reading on the bathroom scale will read Less than when he wasn't helping. This is similar to the reaction that the rear tires feel with soft rebounding front shocks

*So during the time that the front of the car is lifting the front end (but before the shocks are topped out) the stiffer rebounding shocks are applying more force to the rear tires.*

Rear Springs

Rear springs should be fairly stiff for a drag car but many people think that the car should "squat" during the launch so they install softer rear springs on the car to accomplish this. The only cars that should be squatting during the launch are those cars that shock the tires very hard (4-speed cars) and with enough power where the car will overpower the tires. ProStock cars actually squat during launch because they develop enough torque and hit the tires so hard that the squatting helps absorb some of the shock and keeps from overpowering the tires. But, setting up the car to squat is not a function of the springs. It is the position of the Instant Center (IC) that determines how the car squats. The springs still need to be stiff to transfer the force to the tires.