We’ve all heard the benefits of anti-roll, or sway, bars so far as making a car handle better in the turns. But, did you know that anti-roll bars play a major role in helping quick cars go in a straight line also? Many will suggest disconnecting a car’s front anti-roll bar end links to allow the front of the vehicle to raise more easily under acceleration. This promotes more traction at the rear tires, but there’s a lot more going on back there, and a properly designed rear anti-sway bar may be just what you need.

You may wonder why a car specifically designed to go straight would need a bar typically used to help one make turns. For that, we went to the folks who have been helping cars of all makes and classes of racing go faster than their competition – Moser Engineering. Moser’s Jeff Anderson breaks it all down and helps us understand that not everything is straightforward when getting a car to go straight quickly.

Drag racing is the pinnacle of testing a car’s acceleration, so let’s take a look at why a rear anti-roll bar plays such a big role. When a car launches hard, the normal tendency is for the engine’s torque to transfer into the chassis, causing a twist. This torque is countered by opposing forces working in the rearend and tires biting the track.

When a lot of horsepower and torque are applied, the body will lift on the driver’s side and twist in a clockwise motion while the rear tires and differential will try to rotate in the opposite direction, putting more pressure on the driver’s tire and less on the passenger’s side tire, reducing traction.

The more horsepower you have, the more important it is to control the chassis rotation at launch. Likewise, a slick or drag radial will amplify these effects even more than a street tire. This sudden, uneven delivery of force often causes the car to turn to the right, making the driver counter-steer the car to the left. A good anti-roll bar setup on the rear can not only compensate for this, but also correct it and deliver better performance.

As you get closer to what the car needs, it will actually get easier to drive, quicker, and more consistent. – Jeff Anderson, Moser Engineering

Setup & Install Of A Rear Anti-Roll Bar

When it comes to installing a rear anti-roll bar such as Moser’s custom, chromoly anti-roll bar kit, Jeff concedes that there really isn’t a specific location where they work best. “It honestly doesn’t matter in most applications,” he says. “They can point to the front or back of the housing. One thing you do need is to keep the links as close to vertical and as close to the axle centerline as possible.” He goes on to state that there can be a slight angle, but the bar’s effectiveness is reduced.

Moser offers its custom-length anti-roll bar as a complete kit featuring the bar, bushings, end links, and fasteners.

Another aspect that will change a bar’s effectiveness is the stiffness of the bar. Of course, the material the bar is made from will dictate the bar’s overall stiffness. The bar stiffness is also affected by multiple other factors. A larger diameter bar will be stiffer, and the longer the bar is, the softer it will be. The length of arms mounted to the bar also affects how stiff the bar will be. The longer arms will soften the bar’s stiffness, while shorter arms will increase the stiffness of the same length bar. Moser offers both six- and nine-inch arms that are splined to work with the company’s custom-length anti-roll bar stock.

When used on the street, you will have to remember that the stiffer a rear anti-roll bar setup becomes, the more understeer you will encounter. If you plan on using a rear anti-roll bar setup in a drag-n-drive type event, you will need to pay attention when driving in less-than-ideal conditions.

Leaf Spring, Trailing Arm, & Four-Bar Set-Up

An anti-roll bar setup functions the same whether you’re using leaf springs, trailing arms, or a four-bar setup. There typically isn’t much correlation between a vehicle’s rear spring rate and choosing an anti-roll bar’s stiffness, but an anti-roll bar can increase a rear spring’s rate when turning. Jeff also explains to watch out for some leaf-sprung muscle cars that used stiffer rear springs on one side to help counter body roll. This would, of course, need to be considered when initially setting up the anti-roll bar.

A properly set-up anti-roll bar on the rear of a car will help control the adverse twisting caused by the engine’s torque and allow the car to go straight down the track.

A couple of turns of preload is a good starting point for the initial setup of an anti-roll bar. Once you start testing, you may find adjustments will be needed. As you get closer to what the car needs, positive effects of an anti-roll bar upgrade are often measurable in terms of ET and car control. The car will get easier to drive, quicker, and more consistent going down the track.

Just like adding horsepower or stickier tires, the inclusion of a rear anti-roll bar can optimize the performance of our rides. But, similar to honing in on the perfect air/fuel ratio or timing curve, finding the perfect preload to make your car launch straight and true will take a bit of testing. Track time will tell you where it needs to be, so don’t be afraid to adjust and try different settings.