One of the first things I wanted to do after buying a C4 was drive it with the roof panel out. Granted, the pleasures of motoring in a targa-top type of car might not measure up to the joys of full-on, top-down motoring in a convertible, but it would be close enough for me. A good dose of open-air, wind-in-the-hair, sunlight everywhere Corvette action sounded like nothing short of Nirvana.
I mentioned this to another C4 owner, certain he would commiserate fully. Instead, my '87-coupe-owning friend paused and said, "You know, I don't think those cars were designed to run with the roof out." I immediately asked why, and probably a bit stridently at that. "Well," the unbeliever said, "the car flexes like crazy. And you think it creaks with the roof in? Wait 'til you hear it without the roof." I could take no more and walked away, deep in denial.
A week later, I popped the roof out for the first time, for a drive from Los Angeles to San Diego. And you know what? It was noisy. Not the wind noise--that was expected. The car creaked and rattled. A lot. And it flexed. While entering driveways or driving over speed bumps, it was as if the car turned into a giant piece of fiberglass taffy, with giant hands holding one end and twisting the other. I can only imagine how the thing would have felt if I'd been autocrossing instead of cruising. Yet, I knew that I was driving an example of one of the best handling sports cars ever built. So what gives?
As it turns out, that fellow C4 owner was right. No less a figure than former Corvette Chief Engineer Dave McLellan provides some info on the subject in his soon-to-be-released book Corvette from the Inside (This book is excellent reading, by the way; a full review is in the works.) In short, McLellan and crew designed the C4 as a T-roof car, with the "T-bar roof connection" acting as a structural member. Then, GM-exec (and later president) Lloyd Reuss "requested" (McLellan's word) that the car be configured as a targa. The directive, according to McLellan, "came so late that we had no time to rethink the structure to find an efficient solution."
The engineering team added reinforcements to stiffen the car, and the C4's infamous ultra-high doorsills were another attempt to compensate for the loss of the T-bar. I say attempt, because McLellan himself refers to the middle of the car (where the two front rails meet the middle three rails) as having "hinge-like behavior." Given that the third "rail," after the loss of the T-bar, was merely a sheetmetal floorpan, it all makes sense. The C4 team's suspension work allowed the car to be a phenomenal handler, but the problem with excess flexibility and noise remained--and remains today, for those of us who drive fourth-gens, and especially for those who drive hard and sans top.
Tom Gasper, one of the founders of TTR Performance, was also dismayed by his C4's noisy, flexi-flyer behavior when he drove his '96 without the roof. "The wheel hop and vibration were so bad," Tom relates, "that I thought I had a flat tire. The dealer said, 'No, that's how these cars are.'" Rather than settling for driving with the top always on, Tom came up with the Anti-Flex Support Bar (AFSB). The AFSB for C4 coupes is constructed from 1-1/2-inch diameter tubing with .020-inch wall thickness and cold-rolled steel plates. We ordered an AFSB to try out on my '84 coupe, and the results were striking. First of all, the bar (which can only be used with the roof panel removed) is a direct bolt in, with no modifications necessary. The mounting interfaces on the bar are identical to those on a C4 roof, and can be adjusted for variances between individual cars, if necessary.
In short, this thing works. With the AFSB installed in place of the stock roof panel, a quick drive was revealing. Creaking and rattling were notably diminished, as was vibration. And as for body flex...TTR's Ray Davis was on hand when we tried out the bar, and Ray encouraged us to take the '84 through a steep driveway or two. Not only was body flex reduced--a lot--but the "C4 Driveway Double-Creak" had also disappeared. The change was impressive, to say the least. It's as if the "hinge" Chief Engineer McLellan mentions was locked into place, unable to move...which is what we'd guess he had in mind when originally designing the C4 as a T-roof car.
We haven't had a chance to autocross with the AFSB in place--yet--but Davis, a rabid racer himself, assures us that the bar pays dividends on the track, as well. "There's improved visibility, less heat, and more headroom for a helmeted driver," Davis told us. "And the bar structure ties in the front of the car to the rear, so there's no flexing." Tom Gasper assures us that wheel hop is also reduced in racing situations. For those looking to find out for themselves, the AFSB has been approved for use in several types of SCCA and NCCC racing events.
To that, I'll add some personal observations. In addition to the aforementioned noise and flex reduction, my '84 just felt tighter and more solid while equipped with the AFSB, and even more surefooted when cranked over in a turn. TTR's website claims that the AFSB "plants the tires to the ground," and "stiffens your suspension during cornering," and that's exactly how the car felt. And, for the record, the stiffness and noise reduction provided by this bar far exceeds any rigidity provided by the factory roof panel. If I had a garage to park the car in at night, I'd be sorely tempted to put the '84's roof panel aside for the summer and do all my driving with the AFSB in place.