4-bar setup guide

But there is one truth: All race cars all have a neutral line that determines how the chassis will behave see illustration 2 below. If the pickup point is located about this line, the body will separate upon acceleration.

If the pickup point is located below this neutral line, the body will squat. In a perfect situation, the front pickup point should be located near the neutral line. This setup will ultimately work well and prove very stable. The car will neither show squat, nor will it encounter excess body separation.

The dilemma here is how do you actually figure out the neutral line location? Typically the line of thought states that the neutral line of a drag car can be determined by extending a line level with the height of the center of gravity CG until it crosses a vertical line through the front spindle. The neutral line is then represented as a diagonal line that intersects this location and the center of the rear tire-to-pavement contact point see illustration 3 below. Once the front tires are in the air, I do not believe that they have an effect upon neutral line location.

Experience has shown us that the pickup point distance from the rear axles is at least as important as its height.

You should rely on conventional neutral line theory only as a starting point for rear suspension setup. What is instant center? You can find it by simply projecting lines along suspension members to a point of intersection for example, the respective bars of a four-link. Where they intersect is called the instant center see Illustration 4 below. Because the respective brackets found on something like a four-link are under load during acceleration and braking, they must be stout.

When the race car accelerates, the rear-end wraps up, placing the upper bars in tension while the lower bars are held in compression. As you brake, the forces are reversed. The choices made here will determine the length and height of the instant center. These decisions will ultimately impact how the car works. Bickel tells us that if you drive the tire down too hard by way of the IC location, it tends to fold up the sidewalls, which in turn makes for poor surface contact.

Opposite to this, if insufficient force is applied to the tire, it will simply spin without accelerating the race car. Bickel states that if your reaction times are good, a long IC point inches is generally more desirable than a short one 50 inches or less.

This will plant the tires smoothly and keep them planted a long time. However, as we noted much earlier in this article, if too much power is applied to a long IC point, tire shake can result. The other consideration Bickel tells us about is the amount of torque your engine can deliver to the drivetrain coupled with the type of drag slicks you have.

They work best when you limit the rear movement to as little as possible with an IC point on or near the neutral line of the car. That location relative to the rear axle centerline will make a difference in performance, even if the IC point remains the same. The closer to the housing the upper bar is, the less the car tends to wheel stand.

The neutral line examined previously slopes within the car from front to rear. Bickel says that should you decide to change the length of the IC, you must also change the height in order to maintain the same anti-squat relationship.

The farther back you move the IC, the higher it must be. Big power stick shift cars typically need to stay inches above the racing surface. The bottom line here is you have to take your time setting up the four-link for your particular car. Like any other part of the race car, Bickel recommends you follow the above methodology and that you make only one change at a time.

A bit late reply, but: Jack your car up so the wheels are hanging freely. Then adjust so that the pressure point is just resting against the spring. Then tighten everything up and put the car back on its wheels.

I disagree with most of what was said in above article that was the way it was done 20 years ago all info is outdated. I feel a 4 link is superior to ladder bar, but more time consuming to set up. When the 4 link is right their is nothing better for a high horse power car. Hello my name is Robert article from Mr bickel is very informative it leads to a good starting point espically if someone has it allover the place you want the car to move in a forward motion with a minimum wheel stand all is done is a brakage of all peices below chassis.

Every race car is different and the track is the best to test a given set up my experience is the keep it as simple as possible only make one change at a time his article on pinion angle is also helpful. Thanks to Mr Bickel for very helpful article. Your four link information is not great. Four links need to be a parallelogram. By putting them to an instantaneous centre you are inducing twist in the diff housing when the vehicle rolls.

I am setting up a 4-link in my 74 corvette. Why does your line go to cam height over front spindle? Why go through the trouble of weighing the car front to back to find cent. Your email address will not be published. Your Website. Save my name, email, and website in this browser for the next time I comment. This site uses Akismet to reduce spam. After drilling the holes, there was a little burr left from the drill bit.

The weld bung slides nicely into the 1. At this point, the links are ready to be welded. After TIG welding the bungs to the tube, I used my grinder to level the welds and then used a dual action sander with grit to smooth the tubes out. With my 4-link bars all welded up, I am finally ready to get my rear suspension setup and in place.

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