We happened to catch this video when cruising the web, and it prompted many great questions about suspension and – specifically – the anti-roll bar. 

Dave Zimmerman is the owner and namesake of Team Z Motorsports, which has a long history of building full-on race cars in the NMRA and many other series, focusing on everything from street cars to full-on race cars up to Pro Mod-level iron. His comments carry a lot of weight. You’ll notice that Team Z’s rear suspension for Mustangs, specifically SN95 cars, includes an anti-roll bar in the rear, replacing the stock sway bar. But, why?

Here’s the Team Z rear suspension on an SN95 Mustang, specifically their shop car, showing how it’s set up with the solidly-mounted anti-roll bar and control arms.

The anti-roll bar (or sway bar) is basically designed to minimize body roll going into a corner and to a lesser degree plant the rear tires hard under acceleration. A race-type bar like Team Z’s can work far better than the stock bar, though. That’s because for one, the race bar is made of chromoly tubing that is far bigger (1-¼- to 1-¾-inch) and is welded to both control arms connecting them together. Team Z’s bar is also welded to the frame rails, meaning that it works against the control arms to help keep body roll level and – more importantly – to plant both rear tires hard to the ground.

The stock SN95 anti-roll is basically stamped steel from the factory that is mounted with flexible rubber bushings, which causes a lot of flex – certainly more than a large chromoly bar welded in place! Because of this flexibility in the stock bar, it does not work on the rotational forces of the rearend. The stock bar is designed mostly to help prevent excessive body roll, not to plant the tires in a drag racing application. And notice we said “excessive body roll” because you don’t want to completely eliminate body roll either as it allows for weight transfer side to side, which equals better traction and handling. 

You can see there’s not a bit of flex possible in the Team Z bar, which has solid mounting points, compared to stock rubber bushings.

When the object is to drive only in a straight line, it’s a completely different ball game. The number one goal becomes traction and stability. The solidly welded bar works one control arm against the other one to more firmly plant both tires AND keep the body level, whereas a stock anti-roll bar basically absorbs body roll.  A stock bar basically only absorbs body roll since the flexibility is just too “sloppy” to offer all the advantages that a race bar does.

Another shot showing the anti-roll bars of the Team Z setup, which are used basically to plant the rear tires HARD under acceleration, whereas stock anti-roll bars are to control body roll in corners, and are minimally effective at that.