Believe it or not, an anti-roll bar mounted on the rear of the car is a piece of equipment you shouldn’t do without on a street car, street-strip car or even on an all-out drag car. “Huh? You gotta be kidding.” Not so fast roll-meister.
First, let's take a look at why you really need an anti-sway device on the back of a car that mainly see straight line use (and keep in mind that the anti-sway bar does a far different job than a track locating device): The first thing to do is to consider the torque loads placed upon the rear housing. If you haven't considered these factors, you should. George Cathey of Pro Designs (Pleasant Grove, Arkansas – and if you don’t know who George is, he’s the guy who invented the sheetmetal rear end housing) has, and offers this insight:
"Rear axle torque loads are very easy to calculate. First, let's look at a hypothetical set of relatively mild (and easily attainable) car specs:
(a) Engine Torque: 500 foot-pounds
(b) Torque Converter Multiplication factor: 2.2:1
(c) Transmission First Gear Ratio: 2.48:1
(d) Rear Axle Ratio: 4.10:1
Next, plug these numbers into the following (super-simple) formula:
(a) X (b) X (c) X (d) = Rear axle torque load
500 X 2.2 X 2.48 X 4.10 = 11184.8 foot-pounds
"As you can see, the loads that are attempting to twist the rear axle assembly apart (and out of the car) are substantial. If maximum traction is available, then something can break or at the very least, bend."
Engine Flywheel Torque Rotation…
Still skeptical? Let’s back up a bit and see exactly how physics forces things to happen inside a car. Jerry Bickel points this out: “Engine flywheel torque reaction has a decided effect upon how the car reacts the moment the clutch is released or when you leave the line in an automatic by way of a transmission brake or a foot brake. Sir Isaac Newton’s Third Law of Motion states that for every action, there is an equal and opposite reaction. For example, when you fire a gun, it “kicks back” as the bullet is propelled from the barrel.
“In the same way, the engine exerts forces and counter-forces that affect the operation of the car. Pistons and connecting rods apply torque to the crankshaft. Viewed from the front, the crankshaft rotates clockwise. Newton’s Third Law Of Motion applies here. As the crankshaft is turned, an equal amount of torque is applied in the opposite direction to the engine block. Engine mounts transfer engine torque into the chassis, which will try to roll rotate counter clockwise.