A Guide To Buying Aftermarket Rear Control Arms
Aftermarket rear suspension pieces are a dime a dozen; there are so many companies in the marketplace offering these items that you can dial up your favorite retailer and have your choice of literally dozens of tubular control arms for your car, regardless of whether you’re cruising a late-model Mustang, Camaro, or Mopar product like the Challenger or Charger.
In the interest of simplifying the process, we have decided to do much of the legwork for you in this article, where we’ll discuss different materials and designs that are available – with the industry’s foremost experts. This guide should help make a better-educated decision about what’s best for your own project, your goals, needs, and wants. For this advice we went to Maximum Motorsports, Team Z Motorsports, Kenny Brown Performance, BMR Suspension, and Spohn Performance.
While we certainly can’t cover each and every domestic performance-car suspension design for the purposes of this article, it’ll be helpful to understand some of the popular styles and how they function.
There are three different styles of suspension that have been used in the late-model Mustang – the four-link trailing arm arrangement used in the ’79-’04 chassis and the three-link/Panhard Rod arrangement used in the ’05-’14 models. In addition, the ’99-’04 Cobra used an independent rear suspension which we’ll touch on briefly.
GM’s Third and Fourth-Gen Camaro/Firebird platform used a torque arm/Panhard bar/lower trailing arm arrangement. Although the design was slightly different the overall concept is the same. Fifth-Gen Camaros (2010-’14) make use of an independent rear suspension with lower control arms, trailing arms, and toe rods.
In the Mopar realm, the 2005-14 Chrysler 300C, Dodge Charger/Challenger/Magnum all use the same type of independent rear suspension – three links on each side, with a pair of trailing arms and quartet of upper lateral control arms (front and rear on each side).
Although the rear suspension in the Mopar products is independent, the reason you’d want to replace the arms is the same as the other platforms.
The Benefits Can Make You Feel Better
Replacing your factory rear control arms can provide many benefits, from improved handling in the twisties to better straight-line performance if the dragstrip is your thing. Factory control arms are typically manufactured with two things in mind – cost and ride quality.
For that reason, they are typically constructed from stamped steel forms and loaded with rubber bushings that have been designed to suck all of the road noise out of the chassis. In the process, those not-so-strong arms and compliant rubber bushings also suck the life and performance out of your hot ride.
By removing the rubber-bushed factory arms from the equation and replacing them with stiffer, more performance-oriented pieces, you’ll gain greater feel of the road.
Depending upon which type of control arm bushing you use, there will be an accompanying increase in road noise over stock as urethane bushings transmit more noise than the OEM rubber pieces, and the solid rod-end design increases NVH transmission even more, but both urethane and rod-ends offer a large increase in performance capabilities over the factory items regardless of the intended use.
“All of the forces that accelerate the car, as well as much of the braking loads, pass through the rear lower control arms. In stock form, the excessive deflection allowed by the original rubber bushings prevents the rear axle from maintaining its correct position under the chassis. The axle is allowed to shift forwards, backwards, and sideways under the car, leading to poor traction and poor handling,” says Maximum Motorsports‘ Chuck Schwynoch.
He continued, “To improve handling and traction it is vital to control the motion of the rear axle. The key to better axle control is in the bushing design. A proper bushing design will provide precise location of the axle while also allowing the motion required for the suspension to function.”
Upgrading the control arms on your car can provide a drastic difference in performance, but it’s also important to make sure you’re selecting the proper product for your situation – one replacement control arm design does NOT work properly in all applications.
What's Happening Under There?
“Rear lower control arms, along with the upper arms, control axle rotation. All of the forces that accelerate the car pass through the rear lower control arms. The tires rotate on the pavement, moving the axle forward. The axle pushes on the rear lower control arms, moving the rest of the car forward. The control arms, and their bushings, must withstand those forces,” Schwynoch explains.
There are three different materials typically used in control arm construction – DOM (drawn-over-mandrel) mild steel, aluminum, and chromoly steel; each material has its advantages and disadvantages in application.
DOM steel is not actually a type of tubing – instead, DOM is a process by which steel tubing is constructed. DOM tubing has typically been electric welded, and during the manufacturing process the steel is drawn over a mandrel which cold-works the material and gives it more uniform dimensions relative to the inside and outside dimensions of the tube itself.
The cold-working process makes the weld line disappear and the resulting tube to be virtually seamless. Tubing normally used for control arm construction is constructed from 1020 steel, which offers 87,000 psi of tensile strength and 72,000 psi of yield strength.
Rectangular DOM heavy-wall mild steel tube is also used in some applications – its low cost and ease of fabrication make it a prime candidate for a budget-style control arm.
CNC-machined billet aluminum is used in some applications as a material for control arm construction. Billet aluminum offers high strength and extremely light weight, but is not typically used in an all-out drag application as the material is not optimized for higher-horsepower cars.
“These require good engineering and design to ensure they will withstand the loads applied without failing. Unlike steel, aluminum has a finite fatigue life, so that should be taken into consideration when designing anything made of aluminum that is load cycled,” says Schwynoch.
4130 chromoly steel is lightweight – not as lightweight as aluminum, but lighter than 1020 mild steel, and has a high tensile strength of 97,200 psi along with yield strength of 63,100 psi. It’s easily welded with the TIG process. Chromoly has more pound-for-pound strength than mild steel, which permits a thinner wall thickness to be used to save weight and still equal the same structure strength.
Bushing And Bearing Styles
There exists the opportunity to use a number of different materials at each end of the control arm, from rubber (which is typically present in a stock control arm) to urethane, to an all-steel rod end and even a combination of urethane and rod end.
Nearly all of the control arms on the market that are designed for street use have been constructed with the use of a urethane bushing for long life and high resistance to deflection. Team Z Motorsports uses urethane bushings in their Street Beast lineup of control arms with great success.
“We use a proprietary urethane material in our kits. It’s designed so that if you have a 1,000 horsepower street car, you’re not beating the bushings out of it every year – we’ve got the highest durometer bushing that we could find along with the proprietary material, and so far our customers have been hitting high 1.30 and low 1.40 short times regularly with the Street Beast system. With the urethane you don’t get the articulation that you’d get with a rod end, but it’s a tradeoff for a street customer – they don’t want the noise associated with the rod end,” says Team Z Motorsports’ Dave Zimmerman.
Another choice for controlling the motion is a combined design, like Maximum Motorsports’ Heavy Duty Mustang control arms. The chassis end of the control arm uses a unique three-piece bushing design that allows articulation while reducing deflection and dampening the noise transmission on the chassis side, while the axle end uses a spherical bearing that allows for all of the articulation necessary. These are used in street cars making up to 400 rear-wheel horsepower.
During a high-horsepower launch from a standing start, deflection in a standard urethane bushing can cause wheel hop – and as we all know, wheelhop is a parts gobbling gremlin. To that end, if you’re making a substantial amount of horsepower, MM also offers their Extreme Duty control arm design that have spherical bearings at each end of the arm. Unique to this control arm design, Maximum captures the bearing in a machined sleeve. Both Heavy Duty and Extreme Duty designs use a 2-inch diameter steel tube for the arm.
We can’t forget the GM and Mopar machines, either. BMR Suspension and Spohn Performance produce a wide variety of products for the Brand X machines, including the fourth and fifth-generation Camaro among others in addition to their many Mustang offerings.
BMR offers both non-adjustable and double-adjustable lower control arms for the 4th Gen Camaro – the non-adjustable version is available with greasable polyurethane bushings in either boxed or tubular designs, while the double-adjustable version is made in the bushing and rod end versions.
The boxed design and non-adjustable tubular designs are made from mild steel, while the double-adjustable versions are made from 4130 chromoly. Rod end designs use QA1′s XR-series Teflon-lined spherical rod ends.
BMR’s Pete Epple explains, “When you buy a new set of control arms, the decision to use a polyurethane bushing or rod ends depends solely on what you will be doing with the car. If you primarily drive your car on the street and maybe go to the track once or twice a year, a poly bushing is all you’ll ever need. You’ll have a big reduction in bushing deflection over the stock rubber bushings, which will give a big improvement in handling and traction. The car also won’t feel as sloppy, and the ride won’t be harsh because the poly bushing will absorb enough NVH to retain near-stock ride quality.”
“If you are a more hardcore enthusiast, rod ends are the way to go. Rod ends create a solid link between the rearend and chassis, and while this means there is nothing to absorb all of the little bumps in the road, every bit of the car’s power is transferred directly the tires. At BMR Suspension, we also have bushing/rod end combos for the guys and gals that want the best of both worlds. They can get the adjustability and improved performance without all of the harshness associated with solid mounting the arms to the chassis,” he says.
Spohn Performance uses a unique design in many applications centered around their Del-Sphere pivot joint.
“The Del-Sphere joints are designed to have the capabilities of a rod end, where you have the articulation, but we wanted to make something that was greasable and rebuildable that’s a little bit more road-friendly. Instead of the ball sitting on a Teflon lining, it sits in a Delrin bushing, which helps to keep things quieter than a rod end. It has an adjuster ring on it for two reasons – one, so if you need to replace any parts on it you can take it apart and rebuild it, and second, we have a special tool that allows you to loosen the set screw, tighten up the ring a few notches, and it’s like a brand-new joint again,” says Spohn Performance’s Dan Brown.
Spohn Performance offers upper and lower double-adjustable control arm fitments for all of the popular years of Mustang along with the F-Body and the Chrysler LX platforms – their catalog is extensive and widely varied.
Spohn’s Del-Sphere system is included in many of their product lines, along with standard urethane-bushed non-adjustable systems and even rod-end systems in some applications. Spohn uses a mixture of DOM steel and chromoly steel depending upon design, and they even offer a full 4130N upgrade on some of their products.
Relocated Arm Design
Sometimes relocating the position of the control arm can make a very large difference, especially in a drag racing application. The entire point of replacing the control arm in a drag racing application is to lower the sixty-foot time – a better launch will translate into a better overall elapsed time. In most scenarios, if you can improve the launch by one tenth of a second, you’ll gain two tenths of a second on the top end.
The instant center on the S197 chassis is 109 inches in front of the front bumper as delivered from the factory, so it doesn’t really want to work so well. - Dave Zimmerman, Team Z Motorsports
The Mustang in particular benefits from suspension relocation – while the cars work well from the factory in moderately-powered applications, there are definite improvements that can be made. “On the ’79-’04 Mustang chassis, there is no instant center point – it’s non-existent. The suspension is closer to a parallel four-link, and you need an intersect point to go fast in a straight line,” says Zimmerman.
Team Z offers their Strip Series I kit for the ’79-’04 Mustang, which comes with relocation brackets for the upper control arms to get the instant center in the proper location for all-out drag cars.
By using a bracket that fills the holes where the stock bushings would sit, Team Z moves the upper arm mounting position slightly up and substantially forward to improve the instant center location for dragstrip action, and they also triangulate the new brackets to the spot where the vibration damper mounts for improved stiffness.
The 2005-’14 Mustang was prone to substantial wheelhop from the factory due to the control arm location – both the upper and the lower arms can be easily moved with bolt-on parts that substantially improve performance.
BMR Suspension, Team Z, and Kenny Brown all offer lower control arm relocation brackets along with a new upper control arm mount. The lower pieces correct the anti-squat by moving the lower arm down relative to the ground. The revised upper mount design also helps to improve traction, and the BMR and Team Z pieces offer multiple mounting holes for improved dragstrip performance, especially on lowered cars. Each company has their own take on the fix, so it’s best to consult with them dependent upon your intended use for the vehicle.
Kenny Brown’s upper control arm module for the S197 Mustang is unique in that it uses only one hole on the mounting bracket, but they’ve designed the arm to have a slight bend in it. “We run our cars pretty low -the track cars sometimes even lower than street cars would be. The bend is to clear the chassis when the car goes over a hard bump – it’s so the arm doesn’t bottom out on the underside of the car. Our upper arm module only has one hole, and the axle anti-squat brackets only have one hole. Over the years I’ve developed specific geometries that work pretty well. This gives the best combination for street, track, and dragstrip driving, so our customers don’t have to figure out how to adjust it, or make a bad adjustment. They just have to drive, and it works. The same principles that I use to get a car out of a corner are the same principles that someone would use at the dragstrip to get a car out of the hole. It’s all about generating grip,” says Kenny Brown.
Kenny Brown offers an extensive catalog of pieces for all Mustang model years with an intense focus on road racing – the company proves the product on the track. Their AGS complete suspension systems are now in their fourth generation and have been used on scores of road-race Mustangs and street cars to boot, thanks to the incredibly improved geometry.
In addition to the fact that these pieces provide great benefit in the wheelhop department, they also help to provide more bite in the corners by increasing anti-squat and anti-lift to maximize traction and braking capabilities – they aren’t just for drag cars.
“On the S197, the lower control arms are splayed outwards. If you were to look from the top down and extend a line from the control arms to the point of convergence, it would be behind the car. And if you took the point of convergence and ran it through the roll center, that gives you a real roll axis, and on the stock Mustang it points up in the air,” says Brown.
“We use spacers to straighten out the S197 control arms so that they are parallel to center, which means that the roll axis becomes parallel to the lower control arm from the rear roll center. I do that to dial in just a little bit of roll understeer, since the Mustang is notorious for having a tail that wags. The only way to solve understeer on the track is to lift off the gas. Since everyone thinks they can control oversteer with the throttle, and ultimately that leads to ‘I got it, I got it, I got it, I don’t got it’. By altering the rear geometry, I have a little bit of roll understeer which is perfect for the average driver. It’s safer, more fun, and easier to drive the way we set it up.”
IRS Versus Solid Rear Axle
The solid axle is now considered ancient technology, and up until the end of the 2014 model year, the Mustang was the last performance car holdover to use one – thus the proliferation of suspension parts for the S197 and earlier Fox-based platform that have become so ubiquitous at dragstrips across the world.
Current-day performance revolves around the independent rear suspension on the Camaro chassis, along with the Mopar performance offerings like the Challenger and Charger. The independent suspension designs often center around a set of track bars, which could be considered along the same lines as the lower control arms in the stick axle design, but a separate knuckle to hold the axle in place that’s located by at least two upper links.
Where the independent rear suspension shines – and the reason the Mustang finally has one from the factory for 2015 – is in daily-driven applications along with road-racing. The independent rear suspension acts to follow the road much more closely than a solid axle would, keeping the tires firmly planted no matter the situation. Each wheel is able to adjust to changes in the surface without upsetting the vehicle’s overall characteristics.
The advantage to the solid axle design is its simplicity – it’s space-efficient and extremely inexpensive to manufacture. But since it doesn’t allow each wheel to move independently in response to bumps, solid axle-equipped vehicles are much more prone to chassis upset if the surface is not pristine. This is why SRA vehicles excel on the dragstrip, where the surface is flat and forgiving.
They are not nearly as proficient in road-course activity since the wheels cannot (as a function of the SRA design) have any camber angle gain during body roll. In addition, the SRA is part of the unsprung weight of the vehicle, which affects ride quality towards the negative side as the springs and dampers have to work harder to control its heft.
The Chrysler LX platform (Challenger/Charger/300C/Magnum) also uses an independent rear suspension, and Spohn Performance builds control arms that replace the factory pieces in all three positions – trailing arm and both upper front and rear lateral positions.
“Most of the customers we have for the LX platform are based around drag racing and street performance, people that are lowering their cars and need to adjust the camber back out. There isn’t anything from the factory that allows you to adjust the camber other than an aftermarket bushing, which doesn’t provide enough adjustment. We use Delrin bushings in these cars because the factory bushing dimension isn’t very large. We wanted something that was going to be stiff enough to be able to put the power to the ground, and a urethane bushing in this application might have retraction a little bit and take some of the weight transfer away,” says Spohn’s Brown.
The plethora of replacements available to correct factory-designed suspension deficiencies are extensive. As each of the vehicle platforms discussed evolve in the performance aftermarket, the companies servicing those platforms are continually testing and refining their products to give the end user a wide variety of options to allow their vehicle to perform better, whether it’s on the street, at the dragstrip, or on the road course.
We couldn’t possibly provide an all-encompassing list of parts or products for every vehicle platform, but hopefully we’ve helped to increase your understanding of how and why the products are designed as they are. It’s up to you to determine the best product for your particular application. Don’t be afraid to make suspension modifications to your car – in every instance, they will improve and enhance your vehicle’s performance.