Network
In the world of heads-up drag racing, the difference between getting the win light or not can come down to the vehicle that’s able to put the power to the ground most efficiently. Chassis setup and tuning is often just as critical as building a winning engine combination. One of the most important and highly overlooked components of a modern day pro-level race car is the anti-roll bar system that is designed to counteract body roll and translate this movement into equal contact pressure on the tires.
2014 NHRA Pro Stock Champion and current points leader, Erica Enders knows all too well that it takes a consistent race car to run round in the highly competitive class of ProStock. Erica drives a Chevy Camaro built by RJ Race Cars that utilizes one of its Extreme Pro Series anti-roll bar systems.
In this article we will talk with some of the leading ProMod/Pro Stock chassis builders in the country to get their input into the latest trends in max-effort anti-roll bar systems. In order to handle high-horsepower engines, it requires that the chassis components are constructed using the best material available. Pro Drag Radial classes are a perfect example of cars that could benefit from an extreme duty anti-roll bar due to their weight, power level, and the limited contact patch of their drag radial tires.
Anti-Roll Bar Theory
Anyone who has spent any time at a drag strip has undoubtedly seen a car that pulls the left front tire higher off the ground than the right front tire. When this happens, the car is transferring weight from the left rear tire and placing it onto the right side of the car. When the weight is transferred to the right side of the car, the contact patch of the left is reduced, which results in a loss of traction. In small tire, high-horsepower classes like Pro Drag Radial where wheelstands can be common, this can quite literally mean the difference between winning and losing the race.
Frank Mewshaw’s 1988 Pro Drag Radial Firebird is a perfect example of a car that needs an Extreme Duty Anti-Roll Bar. Frank’s car features a 556ci BBC engine fed by twin Precision Turbo 88mm units that generate around 2,800 hp on M1 race fuel. All of this power helps to propel the 3,150-pound car down the 1/8th mile in 4.15-seconds on a 315 drag radial tire.
A drag race anti-roll bar, on the other hand, is intended to keep both rear tires firmly planted on the ground by counteracting the natural torque of the car during launch. Most cars have a natural tendency to lift the left front tire at launch, which is a reaction force due to the direction of rotation of the engine and driveline. The rotation of the driveshaft also tries to push the right rear tire down at launch and the body twists in the same direction. Without an anti-roll bar, the left front of the car wants to lift higher than the right side which could cause the rear tires to unload.
With an anti-roll bar installed, the weight shift from the left front tire is counteracted by the anti-roll bars’ connection to the axle housing which keeps the vehicle’s weight from shifting to the right side, plants the tires evenly, and subsequently results in a level launch and consistent elapsed times. Any flex in the anti-roll bar system can result in inconsistencies in the launch, which is why the construction is vital.
Choosing The Correct Anti-Roll Bar for the Application
When selecting a race-only anti-roll bar, the user must take into consideration the weight and power level of the vehicle. While it is possible to save a few hundred dollars by selecting a heavy-duty anti-roll bar over an extreme power level unit, it is also possible for the shaft and arms to deflect under high-power launches with a heavy car if the materials used are not strong enough to counteract the forces applied to them. Any deflection of the anti-roll bar shaft can result in inconsistent launches. Likewise, if your race car doesn’t make over 2,000 horsepower, then an extreme level anti-roll bar system might be too heavy and bulky compared to a standard anti-roll bar system.
Most drag race cars can benefit from installing an anti-roll bar setup in their race cars. The anti-roll bar is typically installed in the rear suspension to allow the chassis tuner to pre-load the connection between the rear differential and the frame, which leads to consistent and straight launches.
A Tim McAmis anti roll bar system installed in a Pro Mod car. The 3-inch main tube was chromed for this car and the billet 7075 aluminum arms are anodized in red. At the end of the anti-roll bar arm, you can see the connector link and rod end that connects to the rear housing.
The main shaft of the anti-roll bar is typically connected between the frame rails of the car with brackets that are welded to the frame. The brackets are constructed with internal bearings or bushings, depending on manufacturer, which allow the anti-roll bar shaft to rotate freely once installed. Arms are connected to the anti-roll bar main shaft by a splined connection that is secured by a single bolt. The experts, including those from Mark Williams Enterprises, Tim McAmis Race Cars, and Rick Jones Race Cars agree that a splined connection at the arm interface is much stronger than a welded joint. The splined connection also allows the anti-roll bar to be removed from the car for maintenance and inspection, whereas a fully welded anti-roll bar system typically cannot be removed from the car.
“Many chassis builders prefer a non-welded anti-roll bar in high power applications since a welded joint is typically weaker than a splined joint and there’s also a potential for the weld to break where the anti-roll bar arms are welded to the main shaft,” explains Mark Williams of Mark Williams Enterprises.
Material Considerations
In order to work properly, the anti-roll bar must be constructed of quality materials to minimize deflection or bending of the anti-roll bar arms and twisting of the anti-roll bar main shaft. If there’s any movement or deflection within the anti-roll bar shaft or arms, it can lead to inconsistent launches and ultimately a car that’s not able to put the power to the ground. The deflection and twisting of the system can become more pronounced in heavy cars or those powered with engines around 2,000 horsepower and above. In an effort to eliminate any unwanted twisting of the anti-roll bar shaft and arms, component manufacturers and chassis builders are constructing anti-roll bars out of the strongest materials available.
RJ Race Cars’ extreme duty anti-roll bar main shaft starts out as a solid billet steel shaft that’s splined on the outer ends, gun-drilled for weight reduction, and heat-treated for long term strength. The RJ Race Cars anti-roll bar shaft construction is similar to how an extreme-duty axle is manufactured.
RJ Race Cars utilizes a 2-inch diameter billet steel shaft that is splined, gun-drilled and heat-treated for all of its high horsepower applications. The shaft is constructed in a similar fashion to a pro-race axle in terms of machining and heat treatment. The downsize the this approach is that the width of the anti-roll bar shaft must selected at the time of order as these units are all custom-made to order.
Tim McAmis Race Cars and Mark Williams, however, take a slightly different approach to the anti-roll bar shaft construction.
McAmis’ anti-roll bar design centers on a 3-inch diameter chromoly main shaft that’s shipped un-welded. Two billet chromoly spline adapters fit inside of the tube and then are TIG-welded to the main tube based upon the width dimensions required by the chassis builder.
When the diameter of the anti-roll bar main shaft is increased, the torsional rigidity of the shaft also increases dramatically, thus preventing any deflection of the shaft. McAmis noted, “the 3-inch diameter anti-roll bar is approximately 88.7 percent stiffer than our standard 1.25-inch anti-roll bar kit due to the increased torsional rigidity of the main shaft.” Not only does the 3-inch diameter shaft have greater torsional rigidity than a smaller shaft, it’s also noticeably lighter than a solid one-piece ARB shaft.
Tim McAmis Race Cars and Mark Williams Enterprises both utilize welded three inch diameter anti-roll bar shafts. The splined welded hub fits inside of the large chromoly tube after it is cut to the required width, then is fully welded by the chassis shop completing the installation. The anti-roll bar arms shown in this photo are constructed out of billet 7075 aluminum, which is far superior to 6061 aluminum in drag racing applications.
Anti-Roll Bar Arms
Tim McAmis Race Cars and Mark Williams Enterprises both use billet 7075 aluminum arms that are splined to connect to the anti-roll bar main shaft. The arms feature a single bolt that creates tension to hold the arm tight to the splines of the shaft.
A billet splined anti-roll bar arm is suggested by many for a max-effort anti-roll bar system due to the inherent strength of the billet machined part and serviceability of the anti-roll bar bearings. While many mid-to-high horsepower anti-roll bar systems feature a fully welded chromoly construction, where the arms are welded to the main shaft, some experts say this would not be ideal for an max-effort anti-roll bar system due to the added weight of the welded part. When the arms are fully welded to the anti-roll bar main shaft, it also prevents the anti-roll bar bearings from being serviceable since the arms are no longer removable. Williams and McAmis use billet 7075 aluminum splined arms to connect the anti-roll bar main shaft to the connector links.
“Billet 7075 arms have the same strength as mild steel and are roughly half the weight, which makes them ideal for a weight conscious high-power race car,” Williams says. “We initially offered billet 4130 chromoly arms with our anti-roll bar kits, but eventually we changed to 7075 aluminum since many chassis builders didn’t like the additional weight of the chromoly arms.
“Racers need to stay away from billet 6061 aluminum arms in a maximum-effort build because 6061 aluminum is like peanut butter compared to billet 7075,” Williams continues.
Selecting The Proper Anti-Roll Bar
Whether you’re building a purpose built race car or a street/strip machine designed to assault the track on the weekend, selecting the proper anti-roll bar for your application is a critical aspect in your build. While many high horsepower cars that are driven on the street can utilize a high-performance anti-roll bar, most users would have to disconnect while the car is driven on the street due to the rigid nature of a race ARB system. Many purpose-built race cars can benefit from the installation of an anti-roll bar in their vehicle — it’s important that they consult their chassis builder on selecting the proper unit for their intended application. If you choose an anti-roll bar that is not designed for your intended power level, you will most likely spend your weekends fighting chassis issues at the track instead of taking the win light.
RJ Race Cars has decided to go against the grain and offer billet 4130 chromoly arms in it extreme-duty anti-roll bar systems. Rick Jones tells us that the billet 4130 chromoly arms offer increased strength and eliminate any potential for deflection in the anti-roll bar system with this setup. Jones was quick to point out that there are many other areas on the car to remove weight and they didn’t feel that the anti-roll bar system was one of those places.
Anti-Roll Bar Connector Links
The anti-roll bar arms are connected to the rear differential through connector links that feature heim joints on both ends. The connector link main shaft is typically made out of aluminum bar stock in lower power applications, but for the pro-level anti-roll bar, all of the experts we spoke with agreed that welded chromoly link arms are preferred in a maximum-effort application due to the high forces involved. A 4130 chromoly tube with welded end fittings is the most logical choice due to ease of fabrication and length modifications by the chassis builder.
In addition to chromoly welded tube connector links, RJ Race Cars offers its customers billet hex chromoly connector links that are drilled and machined to the customer’s length requirements. The nice thing about the chromoly hex shaft is that it allows the race team to put a wrench on the connector link when making adjustments to the anti-roll bar preload.”Regardless of what anti-roll bar connector link you choose, though, make sure to use high quality 4130 chromoly or 17-4 stainless steel rod ends with your setup. Anything less will eventually lead to play in the anti-roll bar system which can lead to inconsistent launches,” Williams says.
Anti-Roll Bar Installation
The final item to consider when selecting an anti-roll bar is the installation and what is involved for the builder. Most aftermarket anti-roll bars require welding and fabrication in order to complete the installation, so you’ll need to determine if you have the tools and the skill set to complete the installation yourself, or if you should rely on a chassis shop to do the work. These professional level anti-roll bars require cutting and welding to the vehicle frame in order to complete the installation. If you don’t feel you have the skill set required to complete the installation, it might be best to take your vehicle to a reputable chassis shop.
The mounting location for the anti-roll bar also must receive additional bracing and support. Any deflection or twisting at the mounting point for the anti-roll bar can cause the bar to bind in the bearings, which can also result in inconsistent launches,” Jones said.
Here is RJ Race Cars anti-roll bar installed in a Pro-Series car. Notice the x-bracing and gussets around the mounting location for the anti-roll bar. Any deflection of the mounting area for the anti-roll bar can lead to inconsistent launches and poor performance at the track.
Jones recommended that the mounting area for the anti-roll bar receive x-bracing to the roll cage in addition to reinforcement plates and gussets to ensure the area will not deflect or twist during a severe launch. As a leading builder of Pro Stock and Pro Modified chassis, Jones shared that he’s seen many cars in the pits with an anti-roll bar mounted on a straight section of un-supported tubing. This oversight during installation of the part will undoubtedly give the race team headaches as they try to sort out chassis issues to get the car down the track consistently.
Exotic Materials For A Max-Effort Build
Any deflection or twisting at the mounting point for the anti-roll bar can cause the bar to bind in the bearings, which can also result in inconsistent launches. – Rick Jones
All professional drag race teams are looking for areas on the car where weight can be reduced or relocated to a different area to improve the distribution. Exotic materials like carbon-fiber and titanium are being used in more and more locations on maximum-effort builds since these materials are lighter than steel and offer excellent strength-to-weight ratios. And so we asked the experts in this story if there would be any advantage to running this type of material in an anti-roll bar system. Carbon fiber has an excellent strength-to-weight ratio, but in high-stress torsional applications like an anti-roll bar main shaft the material can actually wind up resulting in deflection of the anti-roll bar system, which is exactly what anti-roll bars are trying to prevent. While it might be possible to build certain parts, such as the connector links or arms from billet or carbon fiber, there wouldn’t be a significant weight savings to counteract the increased cost.
There are some places where titanium is appropriate. The main characteristic for titanium is heat resistance. Parts produced from titanium are much heavier than aluminum in the same cross section. Plus it doesn’t have good elastic properties when the material is stressed close to its yield point. Titanium is very difficult to machine, especially when it comes to broaching the splines of a shaft or the internal splines of the anti-roll bar arms.
Anti-Roll Bar Maintenance
The anti-roll bar bearing is a critical component and often overlooked maintenance item for any serious race car. Mark Williams uses a spherical ball bearing with a Nylatron race. Their design is intended to prevent friction and binding of the ARB bearing due to part distortion when the mounting brackets are welded to the chassis.
In talking with the gentlemen included in this story, the unanimous agreement was that maintenance of the anti-roll bar bearings is just as important as setting up the chassis for the track. McAmis tells us, “since the anti-roll is under the car and out of sight, many teams fail to properly maintain the bearings for the anti-roll bar until it becomes a problem. Since the anti-roll bar bearings are greased, this attracts moisture and sand from the pit lanes and return road, which can lead the anti-roll bar to stop rotating freely. When this happens, it causes the anti-roll bar main shaft to stick and become difficult to turn, which typically means that a car won’t put the power down at the track.”
This is relatively easy to fix and often overlooked maintenance item can definitely ruin your weekend at the track.
With a quality anti-roll bar bearing such as the bearing supplied with our ARB kit, there shouldn’t be any noticeable wear throughout a season. – Mark Williams
“With a quality anti-roll bar bearing such as the bearing supplied with our ARB kit, there shouldn’t be any noticeable wear throughout a season. Inspection where it mounts would be common sense–the same as checking critical points on the chassis between events,” Williams says. While most racers won’t have a need for an extreme duty anti-roll bar in their personal race car, it’s important to understand how these maximum-effort units are constructed and that certain components could be used on a vehicle at a lower power level to improve performance, consistency, and handling. Readers should also make sure that anti-roll bar inspection and maintenance is added to their normal pre-race routine as this is an often overlooked item that can cause an owner to chase their car in getting it to perform, or even have a complete failure.
