Garage Storage Organization and Garage Cabinets

2TONE_93GT · 12-30-2005, 04:00 PM

Quote:

If the rear end squats that means that the rear springs/shocks are not pushing the rear tires into the ground. They are just compressing. For the most part you don't want the rear to squat because you want some resistance from the springs/shocks to transfer the force/weight to the tires.

Example:

Make a coil spring out of a coat hanger and place it on a bathroom scale. Push on the spring. The scale is not going to read much because you are not transferring any force to the scale through the softer spring. Now take the spring out of your car and place it on the scale and do the same thing. The scale will read more pressure because it IS transferring more force through the spring.

Four Link and the Instant Center

The goal in setting up a suspension is to apply just enough force to the tires to keep them from spinning and let the rest of the force push the car forward.

Draw an imaginary line through the lower control arm forward. Now draw an imaginary line through the upper control arm forward until it intersects the lower line. This intersection is called the Instant Center (IC).

Now imagine the Center of Gravity (CG) of your car concentrated at the shifter handle. Where the IC (Instant Center) is located compared to the CG (Center of Gravity) is what determines how the force of the suspension acts on the car to get it moving. If the IC is too high then there will be too much energy wasted pushing the car skyward. If the IC is too low then there won't be enough force applied to the rear tires and the tires will spin. There are also variables if the IC is in front of the CG or behind the CG. Somewhere there is going to be a position (or more than one) that will apply just enough force to the tires to keep them from spinning and the rest of the force will push the car forward.

While the car is sitting still, the tires have 100% traction. During the launch you don't want to change this. Properly adjusting the IC will maintain the existing traction during the initial launch or Tire Shock. The IC starts working during the first .001 second of the launch and continues for the next 30 feet or so. However, after the first .001 seconds the shocks are playing a very important roll in "maintaining" the traction and allowing the IC to apply the desired force to the tires. For the most part, the IC is what is adjusted to get the initial hook and the shocks should be adjusted to maintain the traction throughout the 60'.

The four control arms on a four link type suspension, when adjusted correctly for a particular car, can help launch a car quicker and use less horsepower doing it. Compared to a ladder bar suspension a 4 link suspension has the added benefit of changing the length of the Instant Center to accommodate more or less front end lift without adding any more Anti Squat.

Definitions:

Anti Squat (AS):

This is a term used to describe how much the rear of the car will rise during launch. If a chassis has 160% of AS then the rear will rise drastically, planting the tires violently. By comparison if a chassis has 100% AS then the rear of the car will not rise and if a chassis has less than 100% the rear of the car will squat. (See below)

*A common problem with high horsepower cars running too much AS is that the tires will plant the tires very hard for the first several feet but then start to unload the tires and spin when the chassis starts to settle. If your car does this, then look into the value of the AS.

Normal/Neutral Line:

The imaginary line drawn from the tire contact patch through the 50% mark of the Percentage of Rise (PR).

The location of the IC relative to the CG and the Normal Line (or Neutral line) is what determines what the chassis is going to do. One term used to describe the chassis movement for a 4 link suspension is Anti Squat. An IC that is located ABOVE the Normal Line is said to have more than 100% Anti Squat. An IC located BELOW the Normal Line is said to have less than 100% Anti Squat.

* 4-link settings with MORE than 100% Anti Squat will Raise the rear end and hit the tires HARDER.

* 4-link settings with LESS than 100% Anti Squat will cause the rear end to Squat and hit the tires SOFTER.

* 100% = If the IC lies directly on the Normal Line then there will not be any rise or squat. Anti Squat values of 100% should accelerate the car w/o any raising or squatting of the rear of the car.

* IC's that are located IN FRONT of the Center of Gravity (CG) will tend to lift the NOSE of the car.

* IC's that are located BEHIND the Center of Gravity (CG) will tend to lift the REAR of the car.

My General Guidelines for a 4 link:

*Cars that run 10.50 or slower with an Automatic, NO T-brake: 100%-120% Anti Squat with the IC located approx. 5"-15" behind the CG. With a T-brake the 90%-105%.

*Cars that run 10.50 or slower with a Manual tranny: 85%-100% Anti Squat with the IC located approx. 0"-15" in front of the CG. Some manual tranny cars launch better with the IC behind the CG but it all depends on combo and testing will verify where the IC is best suited for a specific combo.

Running less than 100% AS will allow the suspension to absorb the high rpm launches of a stick car. Also, tire size and tire type (Drag Radials vs Slicks) will also determine the location of the IC whether it is in front of or behind the Center of Gravity. The only way to really tell is through testing.

Weight Distribution

Weight distribution plays a roll on how the Percentage of Rise (PR) is determined and how the front end is set up.

If you are setting up a vehicle that is nose heavy, here are some things to try. For ladder bar equipped cars you can raise the IC so that it Shocks the tires harder. Remember that the tires already have 100% traction while sitting still. Shocking or Hitting the tires harder will maintain that traction and help get the front end to start lifting. For 4-link equipped cars you can also lengthen the IC. Fine tuning the front shocks, either stiffer of softer, can get the best launch. Raising the PR can also slow down the 60' if it needs to be raised too far to get traction. When the PR is raised, the energy is directed towards pushing the front end up instead of forward.

If the above doesn't work then increasing the front end travel can have huge benefits. This can allow the PR to remain lower, thus pushing the car forward instead of up and the increased travel will also allow More weight to be transferred to the rear tires.

Remember the example of lifting the board noted above? Let's apply that theory to this scenario. With a stiffer (70/30) front shock we are going to have more force applied to the rear tires during the initial launch. But because the nose is so heavy it doesn't want to lift and the rear tires spin too much. Now we use a softer front shock (90/10). This doesn't apply as much force to the rear tires and causes the tires to hook initially but then spin but does allow the front end to rise. The Further the front end rises, the more force is applied to the rear tires and helps those vehicles with poor weight distribution. So the next step is to try a shock valving of 80/20. Lets' say that this works as expected and nets us 100% traction with just the right amount of front end rise but now we have some more tuning to do. If the 80/20 shock works then there may be Un-necessary front end travel. Remember, we don't want front end travel if we don't need it. So now is the time to start limiting the front end travel until only the minimal amount of front end rise is needed. If this achieved with the proper PR then you can be certain that every bit of energy is being used to propel the car Forward which is what we want.

*The shock valving used in the above examples were used for simplicity only. In actuality Fully Adjustable shocks would be much better so one can adjust the shocks compression and rebounding characteristics.

"Weight Transfer" is a term that is used to mean "shifting" weight to get traction.

Question: If your car Can Not spin the tires on launch, do you need to Transfer the weight?

Answer: No

The reason at this point for transferring weight is NOT to get traction but to allow the front end to rise so the engine can rev quicker and get into its power band. If the car is already in its power band then try limiting the front end travel. There is no need to have any more travel if you already have traction and the car is in the power band during launch.

A perfect example of increasing front end travel to gain traction on the launches was applied to a 1955 Ford PU.

Combo:

557ci BBF, 200hp N2O, 5500rpm stall, Powerglide w/T-brake, 4.56's, 15x33 Goodyear's, Ladder Bar suspension.
*The engine produces approx. 1000 horsepower and launches with the N2O when the T-brake button is released.

The weight distribution of a typical 3000 lb car is 1600lbs front and 1400lbs rear. The truck weighed 3620lbs and the weight distribution was 2600lbs front and 900lbs rear!

Decision:

The PR was left at 59% because it already shocked the tires plenty hard with the N2O and T-brake. The decision was to increase shock travel another 4" with new shocks and then relocate the shock mounts inwards towards the control arm pivot point. This gave the truck a total of 18" of front end rise (up from 8") measured at the middle of the front fender. The front shock settings were also set to slow the front end rise so it would not gain too much energy to lift the front end off the ground and to keep the weight applied to the rear tires during the lift.

Result:

The truck would hook and carry the front tires about 16" off the ground for 40-50 feet just like a ProStock car and then settle the nose back down very slowly with no bounce. The 60' times went from 1.33-1.36 to 1.27.