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April 10, 1998
Making Your Mustang Hook, Part 2
Traction Devices
Now-a-days, it's not uncommon to see a street-driven 5.0 Mustang that has 400 and even 500 hp. With the wide availability of quality cylinder heads and 10 psi from an S-Trim Vortech, power is relatively easy to come by.
Once a person has spent the money to build an engine capable of these power numbers, one of the first things they do is take it to the drag strip for a quantifiable result, an ET slip. Unfortunately, many people are disappointed their first time out and come home with a 1/4 mile ET that is one full second slower than they thought it should be.
One of the most over-looked and taken for granted aspects of a good ET is traction. Consideration has to be given to tire choice, traction bars and other suspension tuning. This Water Box is part 2 in a 3 part series and will discuss traction bars. Part 1 - Tires and Drag Racing can be found in the Water Box Archives. Part 3 - Suspension Considerations is currently featured in the Water Box.
This installment of the "Making Your Mustang Hook" series focuses on traction devices. What follows is a brief overview of what they are, how they work and which ones we recommend.
What are Traction Bars?
The term "Traction Bar" is one that is still used (loosely) to describe a device that helps plant the rear tires during acceleration and increase available traction. They also go by many other names, Lift Bars, Trailing Arms, Solid Control Arms and many others. But they all strive to do the same thing - transfer as much of the car's weight as possible to the rear axle during acceleration.
How They Work
To greatly oversimplify things, during a launch or when under load, the rear axle attempts to rotate upward. If left unchecked, the rear axle will rotate upward to the limits of the flexibility of the stock suspension and then snap back downward in a spring-like effect. This action creates the very undesirable effect known as wheel-hop. It is also the action that causes a suspension to "unload" and loose traction after it initially hooked.
Traction bars take this mechanical energy created by the rear axle rotation and using leverage, lift the front of the car and apply weight to the rear suspension. By limiting the amount of distance the axle can rotate and providing a solid stopping point, wheel-hop is also eliminated (with good tires and quality track surface).
But one important thing to remember is that in order for any rear suspension traction improver to work, the tires must provide enough bite for the rear axle to rotate and apply leverage to the rear. A tire that is spinning does not provide the necessary bite for traction aids to work as they were intended. Even a serious 4-Link type drag race rear suspension will not be effective when used with the Mustang's stock 225 gatorback radials. Many people are disappointed after spending the money on a set of traction bars and labor to install them only to find they are no better off than before - the car still cannot hook.
Pinion Angle
Some manufacturers have produced products that promise big potential traction increases by altering the Mustang's rear pinion angle. The pinion angle can be changed several degrees by using adjustable upper control arms and/or adjustable lower control arms (traction bars).
We spent several exhaustive track sessions experimenting with dozens of different pinion angles on a mid 9 second Mustang (equipped with adjustable upper and lower control arms) and found no improvement over the stock pinion angle geometry. Many of the settings actually hurt the car's 60 ft. times and subsequent performance.
In our experience, the most important thing to consider when setting pinion angle is to ensure that when under load, the driveshaft will be as in-line with the pinion as possible. This usually requires an initial setting of negative 2° to negative 4° so that the pinion aims slightly at the ground. This setting is usually achieved with stock length upper and lower control arm settings. 90% of the traction bars we install are Mega-bites (we'll get into why in a little bit) and even the "seniors" which are fully adjustable end up with a proper pinion angle 9 out of 10 times right out of the box with HP's initial factory setting. To make certain your geometry is correct it's necessary to use a pinion angle gauge, something we do with every traction bar install.
Which Ones Should I Use?
So now you're asking, "Which ones should I buy?" Let us start this off by saying that there are over 25 commercially available traction bars and just about every one we've ever seen does a decent job. The most important thing is that they eliminate the weakness and flexing that is inherent in the factory upper and lower control arms. This is actually more important than corrected geometry. The stock Mustang 4-link rear suspension is actually quite good and capable of impressive 60 ft times with nothing more than adequate rigidity. We have one customer who has gone 10.04 @134.92, with a 1.37 60 ft. with just polyurethane bushings in an otherwise 100% stock rear suspension. The control arms aren't even boxed.
So, with that being said . . . We exclusively use HP Motorsports Mega-bite rear control arms for several reasons. They're extremely high quality, affordable, have some nice features and work well. HP claims improvements in 60 ft times over many other competitor's traction bars. We recommend them for several reasons, but not because we've seen them provide better traction than others. We have had just as good 60 ft times with Southside bars, various tubular control arms and even the old Lakewood slapper bars (one of the first traction bars ever conceived which still work quite well).
But the Mega-bites do offer some serious advantages over others. They feature quality polyurethane bushings as opposed to the solid mount used by Southside and others. These bushings eliminate the severe torque box damage that is so common when using a solid mount. The bushings also transmit much less NVH into the passenger compartment.
The Mega-bites alter the geometry of the rear end, which changes the anti-squat and anti-dive percentages providing increased downforce on the tires. By this, traction under acceleration and braking is improved. And they come complete with spring spacers so the rear ride height of the car is easily adjusted.
There are also other types of rear suspension systems, like those offered by Griggs racing. Griggs developed several road race oriented components that also do a very good job in a drag racing environment. We've installed them many times with excellent results. But for the average drag racer, they're kind of pricey. And when equipped with a set of slicks, we haven't seen any 60 ft improvements over Mega-bites. Griggs claims advantages over others when using street tires but we have yet to test this theory.
So Hook Up and Go
So there it is. An oversimplified explanation of how and why traction bars work and which ones we recommend. But, there's always a catch. As we mentioned earlier in the article, unless you're using a stickier tire than what came with your car, traction bars won't make any real difference. They need at least a little traction before they can begin to fully function as they were intended. We've seen impressive traction from Mega-bites and fairly large BFG Drag Radials, but for optimal traction there is no replacement for a good set of slicks. The bottom line is that you can spend as much money as you want on the rear suspension, but if you're trying to find traction with lots of power and the usual radials, you won't.
There are also many other factors and suspension considerations that can help a car hook, or hurt an otherwise capable suspension set-up. In Part 3, we'll address weight relocation, improved weight transfer and other topics.
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