Roll With It

By Staff Writer
Apr 9, 2009 | Saab | Posted in Suspension & Handling | From the June 2007 issue | Never miss an article

Story By Per Schroeder

We want it all. We want delicious food that doesn’t make us fat. We want dream vacations that are easy on the wallet. And we want corner-carving cars that still deliver a plush ride.

We can’t help you with those first two items, but a simple piece of steel can make that third goal a reality. Meet the anti-roll bar.

The anti-roll bar is simply a U-shaped tubular bar that links one side of a car’s suspension with the other. The middle of the bar hangs from the chassis.

The operation of the bar is just as simplistic as its shape. When the suspension is compressed on only one side of the car—for example, as a car dives into a turn—the anti-roll bar offers resistance as it is forced to twist, working to keep the car level and the wheels planted to the ground. The amount of force needed to twist the bar is its rate.

While stiffer springs at each corner of the car can more or less accomplish the same goal, the anti-roll bar does its job without turning a car into a stiffly sprung coal cart. Since the anti-roll bar simply rotates within its bushings when both wheels are deflected by the same amount, the bar is only along for the ride most of the time. The bar adds spring rate only when it’s needed.

Practical Tactical

The front subframe has to be unbolted to install the anti-roll bar. That’s easier than it sounds.

While anti-roll bars theoretically help performance, what does the stopwatch say? To get some answers, we loaded up our 2005 Saab 9-2X Linear and headed out to Ocala Gran Prix for some testing.

Our extensive testing on this track has given us some great experience with the fast line, and it doesn’t take many laps for us to settle into a rhythm. The Saab 9-2X is basically a rebadged Subaru Impreza, a pretty popular car in today’s scene. As a result, several anti-roll bar options exist.

Our Saabaru’s suspension setup would also work our bars pretty hard. Both the front and rear bars are mounted inboard of the wheel hub, about halfway up the control arm. This setup creates a lever effect—also known as a motion ratio—that acts on the bar as the wheel is compressed. Because the wheel has some mechanical advantage over the bar, it takes a pretty hefty piece to create an effective amount of suspension rate at the wheels.

We ran a series of five laps on our test track for each setup and averaged these times. The track was warm and dry, with air temperatures in the mid-70s. We found that this track’s grippy asphalt is very consistent from hour to hour and even day to day during our testing.

Totally Stock:

Average lap time: 42.16 seconds

Before turning the first lug wrench, we ran the Saabaru in stock condition, down to the original 16x6.5-inch wheels wrapped with 205/55R16 Bridgestone RE92A all-season tires.

Like the Impreza RS, the Linear came standard with a 19mm anti-roll bar on the front and a 13mm unit on the rear. The front bar will take 520 pounds of force to deflect one inch, while the little rear bar will require just 40 pounds for that same amount of movement.

The handling in stock form is a little numb, with a slight bit of trailing throttle oversteer when the driver does something stupid, like lifting off the throttle mid-turn. It’s safe and easy to drive in even the worst of conditions, which is perfect for a rally-ready car like the Saabaru. In stock form, the car circled the track in an average of 42.16 seconds.

Fresh Meat:

Average lap time: 41.60 seconds

Before we began the anti-roll bar testing, we first went to a grippier wheel and tire package—something that would help the car pull a few more g’s. The stockers were replaced with a typical plus-one upgrade, as we went with 17x7-inch Team Dynamics Pro Race 1.2 wheels and 215/45R17 Nitto Neo Gen tires.

The new setup turned in a surprising 41.60-second lap average, providing a much crisper turn-in response and more lateral grip than the OE Bridgestones. The Nittos have a nice, useable slip angle that allows the driver a little bit of leeway at the limit. That 41.60-second average would be our formal baseline number for the anti-roll bar testing.

WRX Rear Bar:

Average lap time: 41.40 seconds

The Subaru Impreza was available with several different rear anti-roll bars from the factory, and the largest of these, the 20mm piece from the rear of a 2002 or 2003 WRX sedan, can usually be found in salvage yards or through the classified section of the North American Subaru Impreza Owners Club (NASIOC) Web site.

This bar is commonly called the FHI 20mm bar, its name coming from Subaru’s parent company, Fuji Heavy Industries. The bar’s 220 lbs./in. rate is a cost-effective mod for any Subaru that could use some extra rear stiffness. We paid just $50 for the bar from a NASIOC member, and it took just minutes to mount.

On track, the Saab felt ever so slightly more neutral at the limit. The car could be coaxed into a little bit of a four-wheel drift by dropping off the throttle at the turn-in point; easing back into the gas would transition the car to understeer as the rear regained traction. The improvement in front grip during sweepers, as well as the new help pointing the nose of the car toward the apex, brought our lap times down a couple of tenths to a 41.40-second average.

Hotchkis Rear Bar:

The Hotchkis rear anti-roll bar next to the Subaru 20mm version.

The Hotchkis rear anti-roll bar next to the Subaru 20mm version.

Average lap time: 41.02 seconds

Next up, we bolted on Hotchkis Tuning’s adjustable 25mm competition rear anti-roll bar. This tubular bar is considerably stiffer than the factory options, while not being appreciably heavier.

Like other Hotchkis products, the bar is extremely well-engineered and an easy bolt-on upgrade. The kit comes with larger brackets that properly support the bar as it is being twisted. We added a pair of Kartboy aluminum end links to the bar to eliminate the flex found in the stock plastic parts.

The Hotchkis bar has three end link mounting holes on each side, allowing the rate of the bar to be adjusted for preference and handling. On the softest setting, with the end links connected to the outermost holes, the bar has a rate of 390 lbs./in. The middle setting is 510 lbs./in., while the stiffest setting is a stout 700 lbs./in.

We chose the middle hole for our initial testing, as that would give us some leeway depending on the car’s track manners. With the big rear bar and the still small front bar, the car was certainly more neutral, with less body roll in the initial portions of the turn. The car could be quickly transitioned to a tail-wagging slide with a lift of the gas pedal and would spin if braking and steering happened simultaneously.

This made for some faster, if a little ugly, laps around our test track. The average lap time dropped about four-tenths to a 41.02-second average, with a few laps being thrown out for excessive roughness.

Addco Front Bar:

We opted to use an Addco one inch front anti-roll bar in place of the stock 19mm piece.

We opted to use an Addco one inch front anti-roll bar in place of the stock 19mm piece.

Average lap time: 40.63 seconds

With just the large rear bar fitted, the Saab had a knife-edge feel at the limit of adhesion—it was too easy to overcook the corner entry and lose momentum with a time-killing slide. As the middle of the corner approached, the front tires were quickly overworked with body roll and throttle to the point where the car would transition to understeer. In theory, a stiffer front bar would tame the corner entry oversteer and control the body roll along with the resulting understeer on corner exit.

The Hotchkis 25mm hollow front bar would have been our first choice thanks to its strong approximate rate of 1190 lbs./in. It’s also available in a kit that is packaged with a Hotchkis rear bar for a reasonable $671. Unfortunately, at the current time, it's only being made for the turbocharged Imprezas. The normally aspirated Impreza’s downpipes interfere with this bar.

As a result, we had to source a larger bar from either Whiteline, who produces both 22mm and 24mm solid bars, or Addco, who offer a one-inch solid front bar with a rate of 1660 lbs./in. (The one-inch bar is comparable to a 25mm piece.) The bar is listed in Addco’s catalog as fitting the 1998 Subaru Legacy, but it works on just about every normally aspirated Subaru product built since 1993. It’s available for about $170 from a variety of online vendors.

We’ve been fans of monster-sized front anti-roll bars since our days autocrossing Volkswagen Golfs, so of course we chose the big Addco bar. The bar is a tight fit in the confines of the Saab’s lower crossmember, but it’s the best way to get a large amount of wheel rate for the front of a Subaru or Saab 9-2X.

We supplemented the bar with another pair of Kartboy end links for the best possible effect. Kartboy end links are available in a package for $180 for both the front and rear pieces. We used a pair of Hotchkis bushings, as they appeared to be a bit more modern in design than the Addco pieces.

The larger front bar was the magic bullet that our car needed. Corner entry oversteer was tamed to some extent, while the corner exit understeer was drastically reduced—that’s assuming that the car was slowed down enough for the tighter corners before throttle was applied.

Our new lap times were another four-tenths faster at a 40.63-second average. There was some oversteer in the faster sections of the track, specifically the entrance to Turn 1. We adjusted the rear bar to its softest setting, which shaved a few more hundredths from our lap times but hurt corner-exit grip. We decided to use the adjustable bar to tailor the car’s attitude for specific tracks and surface conditions.

What We Learned

Sometimes it’s amazing how something so simple can be so effective. In the end, the addition of a pair of anti-roll bars transformed our station wagon into a stable and fun platform with no significant vices.

On the track, our lap times took a nice dip. On the street, we have since logged thousands of miles with nary a squeak or bit of discomfort.

Maybe we didn’t discover zero-calorie chocolate cake that doesn’t taste like plastic or venture on a first-class European tour for just a couple of bucks, but we did manage to mix performance and handling without any downsides. Sometimes it’s the little victories that matter most.

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