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C5 Corvette Sway Bars - Sway, Sway, Go Away

Testing Hotchkis' New C5 Anti-Sway, Er, Anti-Roll Bars

Team Vette Apr 1, 2000
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Let's clear up something right now: Nearly everyone refers to them as "sway bars" or "anti-sway bars," and those bars at both ends of every C5 Corvette most certainly are neither. A "sway bar" would be there to make the car sway, and an "anti-sway bar" would be a device to control or eliminate sway. If we're going to be correct about our terminology, at least as it relates to what the products do, let's call them "anti-roll bars," because their purpose is to control a car's roll (or lean) in corners and turns. Now, with that out of the way...

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When Chevrolet developed the C5 Corvette, the engineers did a marvelous job of crafting a car that would both ride and handle impressively, unlike the bone-jarring ride of early C4s with the Z-51 suspension option. But for serious enthusiast drivers of '97-99 C5s, even Z-51-equipped cars can benefit from stiffer bars. The Corvette engineering staff belatedly recognized this and has fitted heftier front and rear anti-roll bars in 2000 Corvettes with the Z-51 underpinnings.

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Shortly after the C5's debut as a 1997 model, GM's Chevrolet Race Shop began developing a fifth-generation Corvette suspension system for use in SCCA club racing. This system, known as the T1 Suspension Package, is now sold by GM Performance Parts. The need for stiffer anti-roll bars as part of the package led Chevrolet Race Shop's Ken Brown to call on John Hotchkis of Hotchkis Performance with a request that Hotchkis and Race Shop work together to develop a library of larger outside diameter (OD) bars with varying wall thicknesses

The tight confines of the computer-designed C5 suspension presented the first challenge. Any major increase in the bars' outside diameters caused clearance problems if the bars were bent in the factory configuration. While the engineers at Hotchkis developed new bend "schedules," Race Shop's R&D crew designed new, stiffer and larger-diameter frame bushings.

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Ultimately, with the aid of a computer, nine different stiffer anti-roll bar combinations were selected, and several sets of 90-durometer, polyester-filament-lined rubber frame mounting bushings were molded for final testing for the T1 kit. Testing showed that the C5's stock molded-plastic end links for the anti-roll bars weren't strong enough to handle the added stress, so the Race Shop specified Teflon lined spherical bearing end links, which survived severe testing at Daytona and Sebring without a hitch. The tests showed that an extremely stiff set of bars was required when used with the T1 kit's special springs, shocks, and A-arm relocation bracketry. The selected front bar measures 1.5 inches outside diameter with a .250-inch wall thickness, which makes it roughly 200-percent stiffer than a '97-99 Z-51 front bar. The T1 rear bar is 1.062 OD with a .209-inch wall thickness, and is approximately 100-percent stiffer than a '97-99 Z-51 rear bar

Using what they learned from the T1 anti-roll bar development project, Hotchkis began developing a street-friendly, but decidably "sporty," set of bars for everyday driver C5s. Tests run on a 600-foot slalom allowed Hotchkis to finalize outside diameters of 1.25 inches for the front and 1.00 inch in the rear, but more testing was necessary to fine-tune the wall thicknesses. Fun or not, you can't run serious, high-speed handling tests on a local canyon road or sweeping freeway onramps or interchange connectors. Pure and simple, and whether you're worried about getting tickets or don't care, testing on public thoroughfares is too dangerous.

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Then, Lady Luck smiled. Scott Gillman, Product Development Manager at Hotchkis, was observing T1 suspension testing at Buttonwillow Raceway in central California and spent a few minutes between sessions talking with Chevy's test driver, Rupert Bragg-Smith. Scott mentioned that he'd been unable to find an adequate test site and a supply of C5s to use for his final development work. Rupert's response was, "Come out to my school in Pahrump (editor's note: in Nevada, about 60 miles west-northwest of Las Vegas. See "School Daze" on page 28 of this issue for more about the Bragg-Smith school) and you can test during my off season. We have 10 '99 C5 and a private 2.2 mile, 10-turn road course."

Last June 24th, Gillman showed up at the Bragg-Smith Advanced Driving School track, with nine prototype sets of C5 street bars and two Corvette owner friends, Guy Charbonneau ('94 ZR-1) and Jim Moore ('98 C5). After Rupert randomly selected three of his school's C5s as guinea pigs, mechanic Victor Resendez set each of them up with a fresh set of Goodyear EMTs (stock C5 tires) and new, stock front brake pads. Then Rupert said to Scott, "Okay, let's "bed in" the new brake pads and scuff up the tires. This will also show you the 'lines' around the track." Bragg-Smith probably has amassed as many miles behind the wheel of C5s on race tracks as anyone on the planet, and on his own track he's amazingly quick! After a half-dozen or so laps, Rupert pulled in and handed over the Vette to Scott, telling him to, "...learn the track and get used to the stock Z-51 suspension."

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The morning test agenda consisted of running 10 laps in the stock Z-51, followed by 10 laps in an identical C5 with a set of the prototype bars. While two C5s were being tested, the third was being fitted with a different set of prototype bars and the test laps would begin anew, with the stock C5 and one equipped with another set of trail bars. At all times there was a "base" Z-51 car and one with a set of test bars being run, and a third being refit with yet another set of the anti-roll bars. The testers were Bragg-Smith, Gillman, Jim Moore, and Guy Charbonneau. Bragg-Smith represented the pro racer, Gillman the engineer, Moore (who uses his '98 F-45 as a daily driver) the "kinder and gentler" type driver, and Charbonneau (owner of the modified ZR-1 and a veteran of several school sessions with Bragg-Smith) the hard-core enthusiast.

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By lunchtime, the selection was narrowed down to two sets of bars, with 0.134 and 0.151 wall thickness. Each driver ran 10 laps in the "stock" C5, followed by 10 laps in a C5 with the 0.134 bars, then an additional 10 in the car with the 0.156 bars. All four drivers rated the two sets about equal. The tiebreaker was affected by running each of the three cars through the same regimen, but with shaved Goodyear Autocross race tires, subbing for the Eagle EMTs to put additional loading on the bars. That settled it-all four drivers agreed that the thicker, 0.156-wall bars worked best.

Scott "The Engineer" Gillman commented, "The new bars and bushing combo allow for a much quicker turn-in and still let the car slide perfectly neutral in the fast sweeper corners." Jim "Kinder And Gentler" Moore opined, "The new bars didn't effect the ride of the car, and it seemed more stable in the turns." Guy Charbonneau said, "I had never thought of trading my ZR-1 for a C5 until I drove the one with the heavier bars and the sticky tires. Now I want one!" And Bragg-Smith stated, "The car is much more controllable entering the turns. The bars allow you to go faster without the traction control taking away throttle, and they also work well with the active suspension. This will be a great modification for the enthusiast looking for better handling from their street C5, particularly if they want to compete on weekends."

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It's interesting to compare the various anti-roll bars. The Hotchkis 0.156 front bar is 67 percent stiffer than an F-45 bar and 53 percent stiffer than a '97-99 Z-51. The GM Performance Parts T1 front bar is 144 percent stiffer than the Hotchkis bar (or roughly 200 percent beyond the Z-51), which illustrates the need for extremely stiff anti-roll bars on C5s with racing tires, race-spec springs and shocks, and radical (at least by street standards) alignment specs. The rear bars compare almost the same: the 0.156 wall bar is 60 percent stiffer than a F-45, 50 more than a Z-51, and 42 percent softer than a T1 rear.

The Hotchkis C5 anti-roll bar kits, using the 0.156-inch thick wall, were officially introduced at the SEMA Show last November. The kit which is cataloged as PN 2234 and comes with front and rear bars, the upgraded endlinks, bushings, and hardware, and can be fit to both F-45 and Z-51-suspended C5s. Owners who only want to upgrade the endlinks while keeping the stock bars can do so by ordering PN 1797. The installation is simple and straightforward, requiring no special tools and no re-alignment after the bar swap.

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Even cars as good as a C5 can be improved upon, and we're all for bolt-on components that will enhance a C5's already-excellent handling without compromising the ride. Sounds like one of those rare "win-win" situations.


Hotchkis Performance
Santa Fe Springs, CA 90670



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