In past segments of this series, we took a close look at why ARBs work so well in drag racing. To recap the last segment, the torque rotation of the engine tends to increase the traction of the left rear wheel and decreases traction to the right rear wheel. Without some form of correction, this torque rotation will push the car to the right upon acceleration. We also looked at inertia, which, by it self can smoke the tires. Unfortunately, that’s not the end of it either. There’s still more to the equation:
Rear End Torque Rotation
The rear end gears turn the driveline power 90-degrees to the axles, but they actually create rear end torque rotation in doing so. Here’s why: The inertia of the car resists rotation of the wheels, axles, spool (posi, locker, etc.) and the ring gear. The resistance causes the pinion gear to impart rotational force to the rear end housing. Confusing (it is for us too)? Pro chassis builder, Jerry Bickel, suggests we think of it another way: “Imagine that the driveshaft is connecting to a rear facing airplane propeller. As the driveshaft rotates clockwise (viewed from the front), the propeller rotates in the same direction. Like an airplane propeller, a racecar rear end torque-rotates in the same direction as the driveshaft.”
So far so good, but what this rear end torque rotation does is it tends to increase the traction of the left rear wheel and simultaneously, it decreases traction to the right rear wheel. Without some form of correction, the rear end torque rotation will push the car to the right as it accelerates.
So now you’re faced with a plate full of different forces working against the chassis as you accelerate the car. Obviously, as you add both steam under the hood and traction, then the respective forces are magnified. It just means the more you have (power and hook), the more of a handful your car becomes.
Over the years, there have been a couple of quick band-aid fixes used to resolve these issues: One way to control the roll is to install extremely stiff coil springs – with a different bias for each side of the car. Another common approach used in the past and still rather common today is to install air bags inside the back springs (stock spring applications). Then you pump the bags up with different levels of air to counteract the roll. Both of these approaches may limit roll, but both creates a very rigid suspension system that cannot comply with racetrack irregularities. The car is also “lop-sided” when static (typically due to a lot of preload on the passenger rear). They’re not much fun to drive, rubber wears poorly and honestly, they look goofy (been there, done that). If you have a high horsepower car with a four-link suspension or with coil rear springs, the real answer is an anti-roll bar.
Obviously, Band Aid fixes are not what this is all about. Instead, we’re approaching this with a solution that works. In the following photos, we’ll continue our look at drag race anti roll bars. Check it out.
Part I: Go Here
Part II: Go Here
Sources – Loose As A Goose
2450 Smith St
Kissimmee, FL 34744
Jerry Bickel Race Cars
141 Raceway Park Drive
Moscow Mills, MO 63362