There's been a lot of talk about suspension in recent issues of HPP in a series of tech guides. This month we discuss the '93 through '02 F-Bodies, but our '05 GTO hasn't been left out of this mix either, as we recently installed a set of Hotchkis adjustable sway bars. We heard this is one of the most dramatic suspension modifications that can be made to late-model Goats, so we set out to see just why this is, and which settings show the most promise.
In stock trim the GTO has been affectionately compared to Shamu, according to Muscle Mustangs & Fast Fords Senior Technical Editor Steve Baur. The car is less than poised in the corners and didn't handle too well with the narrow 245/40R18 Dunlop Direzza DZ-101 tires. Hotchkis was one of the first aftermarket companies to address these issues. Its adjustable sway bars not only provide a range of stiffness settings, but they're also hollow, thereby reducing weight in spite of their increased size.
The factory front bar is 28 mm in diameter and weighs 18.5 pounds, while the Hotchkis bar is 33.5 mm (1.31 inches) and tips the scales at only 13.5 pounds. It has three adjustment points according to Hotchkis: 37-, 49-, or 63-percent stiffer than stock. The biggest difference comes in the rear bar. They both weigh in at 3.5 pounds, but the 19mm Hotchkis bar has four adjustments that are 50-, 76-, 111-, and 156-percent stiffer than the stock 16mm bar.
Precision Motosports of Florida installed the Hotchkis products, making short work of a seemingly arduous task. It requires a front and rear cradle alignment, as well as a four-wheel alignment, something that is highly suggested even on the softer stock suspension, which tends to come out of alignment after regular street duty.
The Hotchkis sway bars come...
The Hotchkis sway bars come with new polyurethane bushings (and grease) to replacethe stock rubber bushings. These bars are hollow, which reduces weight-the front bar weighs 5 pounds less than the factory one.
We left Precision Motorsports' Odessa, Florida, facility with the bars set at 2 in front and rear. According to Hotchkis, we were 49- and 76-percent stiffer than stock at this point, and we could really feel it. Bob Morreale at Precision demonstrated the increased performance for us and we were impressed.
Our initial autocross testing on the stock bars showed us surprisingly impressive times from the GTO in stock trim, and a 0.845 lateral g average on the skidpad. This was a hairy experience, and you could hear the car yelling back as it surrendered to the extreme body roll. Justin Cesler, GM High Tech Performance technical editor, said the car looked sloppy and had an extreme amount of body lean. It almost lifted the inside tire under extreme cornering, and it felt unsure.
For the Hotchkis bars, our testing facility was the Gainesville Raceway. In addition to it's world-class dragstrip, the facility also has a road course that allows for repeated, consistent testing. Our driving impressions were derived from the road course, and our lateral g numbers were found on the 200-foot skidpad.
With the new bars under the car, the on-the-road feeling was immediately improved, so we were excited to see how much more performance we could get with these bars through tuning at the track. To begin with, they were adjusted to their loosest setting, 1 and 1. Tire pressure was raised to 40 psi to prevent the tire from rolling over, and we took our laps around the skidpad and the road course. The improvement was noticeable, but not dramatic compared to stock. The GTO uexhibited a tendency to understeer.
At 33.5 mm, the Hotchkis front...
At 33.5 mm, the Hotchkis front bar has a larger diameter than the stock 28mm non-adjustable bar.
For our next stint, we moved the rear bar to the No. 2 position in effort to achieve more neutral handling. This made a sharp jump in feel and the car seemed more controllable. Around the skidpad it felt more settled, and our numbers reflected that.
Changing the front to the No. 2 setting seemed to clean up the front-end wander. It stiffened the front and reduced body roll.
Hotchkis' front bar has three...
Hotchkis' front bar has three adjustment points for stiffness. The hole furthest to the left is the softest setting, since it provides the longest swing arm length.
The rear bars work the same...
The rear bars work the same way, with the outermost adjustment hole being the softest.
Precision Motorsports of Florida...
Precision Motorsports of Florida installed the sway bars, and handled the cradle and four-wheel alignment. The alignment specs are stock.
We jumped the rear bar up to the next setting, No. 3. After taking a few hard corners, things felt right on the road course. The GTO felt balanced, like the only thing holding it back was the tires. We settled in for the skidpad, knowing these had the potential to be our best numbers. The results speak for themselves, as the recorded grip was the best of the testing.
Despite this, we tried stepping the rear bar up to its stiffest setting, No. 4, but the back end seemd too stiff and went into oversteer too early. With a softer tire, the stiffer settings may prove to be ideal. The front bar wasn't put beyond No. 2 because of rumors of the factory endlinks bending.
After the day was through, we concluded that the improvements seen and felt with these sway bars are substantial. You would be hard-pressed to find a larger improvement from a single upgrade other than tires, but tires won't reduce the body roll. On our GTO, we found setting No. 2 up front and 3 out back were the clear victors, from the driver's seat and in the numbers, as they improved vehicle control dramatically.
|200-FOOT SKIDPAD TESTING
|| AVERAGE LATERAL GRIP IN "G"
| Run 1
| Run 2
| Run 3
| Run 4
1. While these settings are stiffer than stock, the Goat didn't feel very controlled. There was noticable lean, especially in the front.
2. These settings certainly were felt in the back of the car, but the front tended to wander in transitioning corners around the road course.
3. These settings felt very confident and were what kept when leaving Precision. It did, however, feel a little tense when brought to the edge of grip.
4. At 2 up front and 3 out back, the GTO felt very balanced on our 300-wear-rating street tires. Any understeer was very easy to overcome with the throttle, and the car was extremely easy to drive on the edge of control around the skidpad, unlike Run 3.
|HOTCHKIS SWAY-BAR SPECS
||15/16 inch (33.5 mm)
||37, 49, 63
||3/4 inch (19 mm)
|| 3.5 lbs
||50, 76, 111, 156
On the street, the new sway...
On the street, the new sway bars make a significant difference. Turn-in is more precise, and steering response is improved without affecting the ride quality.
While out at the track, a...
While out at the track, a friend helped us onto a pair of ramps so we could easily access the endlink bolts in the front and rear.
After our first laps around...
After our first laps around the skidpad in both directions at Gainesville Raceway, we decided to increase the stock tire pressure from 32 to 40 psi. It's suggested that you run higher-than-normal tire pressure on the skidpad to prevent the tire from rolling onto the sidewall.
Testing began with the front...
Testing began with the front and rear bars in the No. 1 position (softest setting). Here the front bar is in the No. 2 position, which ultimately provided the best handling on the road course and the best skidpad numbers in testing.
In the rear, the No. 3 position...
In the rear, the No. 3 position resulted in the best overall handling in our testing.
We carried some serious speed...
We carried some serious speed through the slalom, and our GTO was the fastest car we tested on street tires that day. Our testing has shown that there is a considerable amount of adjustment with these bars, and they have a strong effect on handling and driving confidence. We can't wait to see what these things can do on a stickier tire.