Most of us have heard about sway bars, and can recognize them when we see them. But what do they do? Quite simply they control the transfer of weight from one side of the car to the other. When does this happen? Why when the car goes around a turn. When the car leans over, from the force of inertia, the stiffness of the bar, which is the only component connecting both corners of the car, resists this action. That is why they are commonly called roll bars.

When you look at the tube frame GT1/Trans-Am cars you immediately notice that the sway bars are different from your street car, or a stock car. Not only do they look different but they are in a different location. That is partly by necessity, partly from design even thought they serve the same function. We will look at each of the two separately. For the purpose of this discussion we will only be talking about the front bar.

On the stock car the bar is typically mounted as low as possible, in front of the wheels. Earlier designs were mounted in two blocks on the bottom of the frame rails, like your street car. Newer designs place it inside a tube which connects the frame rails. This allows the car to be run at a slightly lower ride height. The arms are removable and slip onto splined ends on the sway bar itself. These arms connect the bar to the lower control arm. This design, while not adjustable, is simple and effective.  Its placement is made possible by the “kickup” on the front subframe.

The first thing you notice about the swaybar on a tube frame GT car is its placement. Unlike the stock car, it is mounted high, above the upper frame rail, and generally in front of the wheels. (see the picture above) The reason for this location is that these cars use a flat frame rail. Thus there is no room under the car to mount the bar. The bars are generally mounted in one of two ways. The traditional way is for it to be sandwiched in a pair of split blocks bolted to the upper frame rails. Some newer designs have a heim joint threaded through the bar itself, this is simply attached to a bracket on the upper frame rail with a bolt. Regardless, it like the stock car design is connected to the lower control arm. In this case be tubular bars with heim joints in either end for adjustability of length.

The ends on these  bars are a mixture of fixed and rotating ends. (see the picture for an example of a fixed arm) The fixed arm, while it has different mounting locations  for the links, is not adjustable once attached. The rotating end is unique in that it is driver adjustable while the vehicle is in motion. It consists of a flat bar which is bolted to the sway bar. Mounted inside a bearing on the sway bar, it is free to turn.  The other end of course is, like the non adjustable end, attached to the control arm via means of a link. Driver adjustablity is by means of a cable run back to a quadrant mounted inside the cockpit. By moving the lever the cable causes the blade to be rotated from the vertical. This reduces its ability to resist the vertical forces on it, thus reducing the resistance to roll. While this provides the driver with an ability to reduce handling  problems during the race it is not perfect. The change is not linear. There is no constant amount of change per movement of the bar.

This of course is just a simplistic explanation of sway bars, and I welcome your comments.

Example of sway bar mounting on 2011 Trans-Am car.

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