Adjusting That Rear End: Get Traction Under Control

In taking that hot-rod to the drag strip, you’ve found that there’s a lot more to it than beefing up an engine and punching the throttle. You’ve spent as much time and money as you want under the hood and on the trans, but now you’re looking to get traction under control.

Getting the power to the ground is done in a lot of ways. So, let’s take a look at some common mods and how they impact rear wheel drive performance on the track. To keep things simple, let’s assume you already have a good set of tires and the correct differential and ring gear selection. That allows us to focus on the suspension end of things, as well as some simple solutions to aid traction and why you may want to consider them.

Why bother?

The first time you hit the track, you may run into some issues with getting the rear end to hook up just right. Axle wrap, wheel hop, and poor shock/spring selection are serious killers of traction, and if you can’t seem to get a grip, these are often the cause of the issue. These can manifest as wheel spin, wheel hop, sluggish 60-foot times, etc…

So, let’s work from the simplest solutions to the most complex—a process you should use for all trouble-shooting. Not only does it save you money, but it keeps you from taking redundant steps. Try one upgrade at a time and see how the vehicle performs as they are made.

Shock Absorbers

“With any suspension arrangement, mistakes can be made which will set back any racing program. It’s imperative to not battle the set-up, and find what works best sooner, rather than later,” advises DragZine. And the most common mistake? Using a crummy shock. So, if you can’t seem to get the car to hook up and are running non-adjustable shock absorbers, this is the place to start.

A set of single or double-adjustable shocks are highly recommended for all four corners of the car. Single adjustable shocks are great for the enthusiast who hits the track occasionally, while double-adjustable shocks are best used for more serious applications.

Front

When looking for shocks, keep in mind that the rear set up isn’t all that comes into play when taking off. What happens in the front of the car will have just as much impact as the rear. That means, to get a handle on the rear, you will need to do some work up front.

“Drag racing isn’t about cornering forces or handling: it’s about weight transfer,” explains Michael Harding over at Mopar Connection. “The ultimate goal is to control the wheelie and get the weight on the back end of the car. Now, this doesn’t mean you need to get the front end in the air every launch, but what you want to do is control that launch better by getting the front end lighter and the rear end heavier.”

If the car is bouncing or jerking violently, it’s important to note at which point. On launch? After launch? During gear changes? This will help you determine how stiff to make the shock extension setting in order to get better weight transfer. Just remember, “The more violent the car can launch, the more critical the shocks have to be,” advises Mopar Connection.

Rear

Out back, setting up the shocks is done to get the tires to hit the track and keep them there. You want to get a handle on the initial bite and keep the tire forced down. Adjusting rebound is going to allow you to find the perfect setting for that initial bite. Then, the compression characteristics of the shocks will come into play as this is the force that will hold the tire to the track.

Keep in mind that properly setting the shocks is relative to the vehicle so there’s no one universal configuration. “Another thing to remember is that consistency is the goal, not always the lowest possible 60ft time,” says Dave Kass of QA1, an industry-leading manufacturer of performance suspension components. “The more consistent your launch is, which will vary throughout the day as the track heats up and more rubber gets put down, the better you’ll be able to judge your car at race time.”

Suspension Set-up

There are two common suspension set-ups found on typical rear wheel drive vehicles at the track: 4-Link and Leaf Spring. Considering 4-link systems dominate the late-model market and even some classics, let’s start there.

4-Link

If you’ve updated your shocks and are still in need of traction, you can look to upgrading the coil springs in your 4-link system. Generally, factory springs are softer to accommodate daily commuting, making them less than ideal for drag racing. Stiffer springs are a great way to aid in transferring power to the ground and with mild set-ups, this may be exactly what’s needed.

Beyond just grabbing a stiffer set of springs, you should also consider lowering the vehicle. This will bring the center of gravity down and help increase traction. But, keep in mind that lowering ride height changes the geometry of the rear suspension. If you don’t adjust or replace appropriate factory components, lowering your ride can actually result in worse traction and wheel hop.

“The stock control arm mounting position is fine for stock height vehicles, but once you lower your car, the control arms change and need to be corrected,” explains BMR Suspension. “Our control arm relocation brackets allow you to correct the lower control arm angle, correcting the rear suspension geometry and allowing you to add anti-squat for increased traction.”

Leaf Spring

On most classic applications, you’ll find leaf spring suspensions. Leaf springs are outdated systems but this does not mean they don’t have the ability to perform. Think about it: for years, racers have been pushing leaf spring vehicles into ridiculously low ET ranges so there’s no reason to believe you can’t do the same.

There are several ways to get more traction with leaf springs. One age-old option is to swap in a set of stiffer springs. Stiffer leaf springs can work to prevent multiple issues in one swift blow, making this a great place to start updating. However, they aren’t an all-in-one solution and they’re not the only solution to help get traction under control. In fact, most serious competitors lean toward single leaf set-ups (or “mono-leaf”) with the aid of traction devices, as opposed to multi-leaf systems.

Traction Bars

The big issue facing leaf spring racers is axle wrap. This is when the axle physically tries to twist and “wrap” itself under the leaf spring, as power is applied to the rear wheels. “Basically, the leaf spring tries to turn itself into an ‘S’,” explains DragZine. “A traction bar, like Calvert Racing’s CalTrac bar, is designed to eliminate axle wrap by stopping the rotation of the leaf spring.”

There are many different kinds of traction bars available, as they are a very cost-effective way to battle axle wrap. CalTrac bars are particularly innovative in that they are adjustable. This means you can truly dial them in to work as best as they possibly can on your application—making them a great solution for serious competitors.

Calvert Racing also offers its unique Split Mono-Leafs. Used by drag race enthusiasts across the nation, these springs are considerably lighter than factory multi-leaf springs, offering unsprung weight savings. They also allow for various ride height options and are designed to work in conjunction with CalTrac bars.

Pinion Snubbers

Another way to keep those leaf springs from twisting up is by using what’s called a pinion snubber. This unit bolts to the top of the differential and engages the car’s floor during axle wind up. “Since the snubber tries to lift the car at this point, the rear differential is actually forced downward and improves rear traction,” explain the folks over at HotRod Magazine.

“Stock pinion-snubbers can be as much as 3-4 inches from the car’s floorboard, allowing the axle to wrap up quite a bit before the snubber hits the floor. By moving the snubber closer to the floor, by shimming or modifying the stock snubber, or by installing an adjustable pinion-snubber, axle wrap up is reduced and traction is improved.”

Ladder Bars

For the most part, our solutions so far have been geared toward the more casual enthusiast. Though, there may come a time when it’s worth looking at more advanced solutions, especially considering the modern standard of power and performance.

Commonly found on off-road 4x4s, ladder bars get their name from their design: two long bars with multiple small bars in between, resembling—you guessed it—a ladder. Generally, they are wider on one end, which gives them a triangular-shape.

Mounting to the axle and the frame, the ladder bar prevents wrap-up by holding the axle in place when power is applied. The torque created when the axle attempts to rotate is then transferred through the ladder bars and into the chassis, lightening the front end and transferring weight to the rear, which plants those tires to the ground. “By stabilizing the axle housing, wheel hop is virtually eliminated, acceleration is smoother, and parts breakage is minimized,” explains Moroso Performance Products, one of the world’s most respected suppliers of racing and street performance equipment.

Keep Things Balanced

As you make upgrades and adjustments to the rear suspension, always keep in mind that there is no universal solution. Looking at what the pros are using and how they set their cars up is a great way to learn, but you should always keep in mind that what works for their driving habits and their car may not be the best for yours.

It’s going to take some testing and tuning to find what works best for you. While that sounds like a pain, it’s extremely exciting because that means you will not only get to drive your car fast but find out how to make it even faster at the same time.