MM News

Make Driving Fun! Ultimate Traction with a Torque-arm

Topic #8 from our series.

Read on for more expert advice on transforming your Mustang into a high-performance handling machine. This week's topic is all about the Torque-arm: what it is, how it works, and the handling boost it brings. (If you missed the previous episodes, they're posted on our website in the FAQs & Tech Tips section.)

Searching for more rear grip for your ride? You're not alone! Everybody wants more traction for their Mustang—not only when launching in a straight line, but to get more grip in all situations. More rear grip provides greater straight-line traction, higher cornering speeds, better braking, and the ability to accelerate out of corners sooner and harder. More grip provides a more stable, more predictable, safer, and more fun to drive car. Mustangs always need more grip!

OK, I'm listening. So how do I get more grip?
Short answer: install a Maximum Motorsports Torque-arm Suspension System. It's the key to maximizing rear grip for a solid-axle equipped Fox/SN95 Mustang.

What's a "Torque-arm Suspension System"?
MM's complete Torque-arm suspension system consists of 3 major parts: Together, these parts change the stock Mustang 4-link suspension design into a Torque-arm suspension design, which is a variation of a 3-link suspension. Changing your Mustang's stock suspension to this superior design gives your Mustang more rear grip and all the benefits thereof, including:
  • More straight-line traction
  • No rear axle wind-up, the primary cause of wheel hop during acceleration
  • Greatly improved cornering and corner exit acceleration
  • Superb control and predictability
  • More wet weather traction
  • Much better braking and ride quality

What is a Torque-arm, anyway?
It's a long suspension arm that attaches between the rear axle housing and the chassis. Its primary job is to control axle housing rotation. It has to be used with a lateral location device such as a Panhard Bar. (See last week's newsletter about Panhard bars for more info on that critical piece of the Mustang suspension puzzle.)

So, did Ford do it wrong or what?
Not really, but if you want a great-handling car, you can do way better! Let's look at the problem with the stock Mustang rear suspension:
  • All 1979-2004 solid-axle equipped Mustangs have the same 4-link rear suspension first designed for the 1978 Ford Fairmont. That suspension was designed for cheap manufacturing and use in what driving fans politely call a "transportation appliance." It has disastrous limitations in performance applications.
  • The lower control arms have 2 main jobs. First, working along with the upper control arms, they control axle housing rotation. Second, they transfer acceleration forces from the rear axle into the chassis. During acceleration, the rear axle pushes on the lower arms, which in turn push the car down the road. All forward acceleration loads go through the lower arms.
  • The upper control arms also have 2 main jobs. First, working along with the lower control arms, they control axle housing rotation. Second, the large opposing angles of the upper arms laterally locate the rear axle housing; they keep the chassis centered over the axle housing. During acceleration, the rear axle pulls on the upper arms.
  • Virtually all 4-link rear suspension designs, including the Mustang's, are over-constrained. This means the rear suspension can't move into all possible combinations of ride height and roll angle. If your car is more to you than a transportation appliance—or if you encounter an emergency while driving—you need much more capability than this stock set-up allows! To get that, the control arms need to change length. Ford gets away with their problematic system by installing large, soft rubber bushings in all 8 locations. This allows the control arms to change length, but also causes other bad characteristics, such as unsettling instability caused by a rear-steer effect and dangerous snap-oversteer during hard cornering.
And here's how the Torque-arm suspension system corrects this mess:
  • The Torque-arm controls rear axle housing rotation.
  • The rear lower control arms transfer acceleration loads into the chassis; all they do is push the car down the road. They have nothing to do with controlling axle rotation.
  • The Panhard Bar provides all lateral location.
  • This design is not over-constrained and allows the rear suspension to move smoothly into any combination of ride height and roll angle.
  • Those components do all the jobs the 4-link did; there's nothing left for the upper control arms to do. They are no longer needed and are discarded.
  • Each part is dedicated to a specific job, and so each can perform its function without compromise. Problem solved!

The Internet says the stock suspension design causes binding, which causes snap-oversteer. How does a Torque-arm suspension help?
Ford designed the Mustang suspension to understeer. It works as designed until the body rolls to an excessive point during hard cornering, and then the rear suspension bushings bind up (in other words, they allow no further movement). The bind effectively causes a large and sudden increase in rear roll resistance, which causes the sudden onset of oversteer. There's your understeer and then snap-oversteer situation. It's not pretty and can be very dangerous.

Many aftermarket rear control arms make the snap-oversteer much worse. Their bushings are often designed with such a focus on reducing fore/aft deflection that they also prevent the angular movement required for the suspension to articulate properly. That increases suspension binding. Upper control arms are especially sensitive to binding up due to their relatively short length and significant opposing angles.

Another popular option is to install aftermarket control arms with spherical bearings. This eliminates the problem with resistance to angular movement, but still doesn't allow any length change, which is absolutely required in a 4-link suspension. This results in the most binding possible. The set-up works on a very smooth drag strip, when the rear suspension doesn't allow appreciable body roll, but in any other situation (which is pretty much all the time) it causes very poor performance.

MM parts end binding and snap-oversteer. Period.
The Torque-arm suspension eliminates the 4-link upper control arms, the main source of suspension bind. But for truly outstanding handling improvements, the MM Torque-arm has a patented front mount design that allows plunge and rotation, so there's essentially no binding in any situation.

The MM Panhard Bar uses spherical rod ends, so there's complete freedom to articulate during suspension movement to any required angle. The result is no suspension binding.

MM Rear Lower Control Arms use spherical bearings and/or special 3-piece urethane bushings (varies with the particular control arm version). The MM designs ensure virtually no suspension binding.

See a pattern there? The MM Torque-arm Suspension System eliminates even a hint of snap-oversteer.

Awesome, but I'm a major car nerd. Tell me about the really technical stuff, like Instant Center and anti-squat percentage.
Cool, so are we! The Instant Center (IC) for the Mustang 4-link (with stock, unmodified geometry) provides anti-squat in the neighborhood of 70% at stock ride height. The anti-squat percentage increases when the ride height is lowered from stock; at 1" lower the anti-squat is about 90%.

The IC for the MM Torque-arm provides anti-squat in the neighborhood of 130% at stock ride height. Unlike the stock 4-link, with the MM Torque-arm the anti-squat percentage goes down when the ride height is lowered from stock; at 1" lower the anti-squat is about 110%.

With a 4-link, the IC moves up/down and fore/aft as the rear suspension moves. With the Torque-arm, the fore/aft location of the IC is fixed, and doesn't change when the suspension moves. The IC height still changes with suspension movement, but to a lesser degree than with a 4-link. The greater stability of the IC location keeps handling behavior more consistent.

Is a Torque-arm okay for street driving, or is it just for drag racing or road racing?
The MM Torque-arm is great for all kinds of driving, making your Mustang both safer and way more fun. Increased rear grip helps in every type of driving. As Mustang owners ourselves, we never complain about too much traction!

Well, this all sounds terrific. How do I get a Torque-arm suspension for my Mustang?
Easy! Visit the Maximum Motorsports website. We've got several Torque-arm system packages, plus individual parts and the tech you need to choose what's best for your Mustang. Knowledgeable MM Tech Associates are just an email or phone call away.

Thanks for reading! Stay tuned for next week's illuminating newsletter No. 9, where we'll explain the frustrations of bumpsteer, how it affects your life, and how to keep it to a minimum.