Torque Arm Suspension Systems - How It Works

Want killer handling for your muscle car? BMR’s torque arm suspension systems offer an interesting alternative to the common four-link upgrade

Stephen Kim Apr 24, 2012 0 Comment(s)
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Straight-Line Hook

In addition to maximizing lateral grip, BMR’s Torque Arm Suspension system can be tuned to enhance straight-line hook as well. We provide multiple control arm mounting holes for adjusting a vehicle’s antisquat characteristics. Every vehicle has an imaginary point where the suspension links would converge if they were extended forward. This is known as the instantaneous center. The instant center is a virtual lift point for the suspension, and it will dictate the vehicle’s attitude under starting line acceleration. If this point is too far forward, the car will squat, wasting energy without hitting the tires hard enough to transfer weight properly to plant the tires. If the instant center is too far rearward it has an opposite effect. Each car will have a different instant center location based on the vehicle’s center of gravity. Having some form of adjustability, as provided in BMR’s suspension system, allows the user to find the sweet spot of their specific vehicle.

Rugged Construction

Since suspension components must endure tremendous loads, only the finest materials are used to ensure that BMR’s torque arm kits are as durable as possible. All round tubing used in the construction of our torque arm kit is 0.120-inch wall thickness DOM. We use a combination of 3/16- and 1/8-inch laser-cut steel for all of our mounting plates and gussets. Additionally, our Watt’s link is mounted in double-shear fashion, and our torque arm is mounted to the rearend with a 1/2-inch-thick steel plate that practically doubles as a rearend reinforcement. All machined components are 4130 chromoly steel, Delrin, or 6061-T6 aluminum. Likewise, all mounting hardware is Grade 8 steel.

NVH Control

Considering that a torque arm attaches directly to the rearend housing, extensive efforts have been made in BMR’s kits to prevent road noise and vibration from being transmitted to inside the cabin. The front mount of the torque arm has a telescoping, Delrin-bushed slider with a large-diameter polyurethane bushing to isolate road noise from the chassis. The Delrin bushing allows bind-free articulation, while the polyurethane bushing minimizes deflection while still providing some compliance for NVH control. Our poly bushings are greaseable by an external grease fitting. The grease travels through flutes internal to the bushing, lubricating the center sleeve, then moves outward to the thrust surface of the bushing.

To Sway or Not To Sway?

With the ability to fine-tune rear roll center height, a rear sway bar is not as necessary as many may think when using BMR’s Torque Arm Suspension system. Most suspension systems don’t allow any adjustment of the rear roll center height, making a rear sway bar absolutely necessary for tuning out oversteer or understeer. The roll axis is an imaginary line running longitudinally from the front roll center to the rear roll center. Altering the height of the rear roll center changes the angle of the roll axis, allowing the user to choose how much oversteer or understeer they desire. In some circumstances, there just isn’t enough adjustability and a rear sway bar is still necessary to neutralize the platform, or to provide the desired handling abilities of the car.


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