A couple of random thoughts:

If the coupe is still classified as a convertible for safety purposes, and if the roof is not classified as a rollover structure, are you really any better off with the coupe ? Or is the thought that no one will pay attention to it at a track event because it looks like its OK ?

I have always understood that a convertible loses chassis stiffness because there is no connection between the windscreen frame and the rear of the chassis. How can this roof add stiffness if the center area is still open ?

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John
Lexington, KY
Sky VIN 00252
5-Sp Manual
Midnight Blue

The GM reps I talked to there informed me the Coupe roof did provide more protection in a roll over than the Convertible, it's just not required to be rerated by the HSTC.

It's not only the lack of connection from front to back, it's mainly the connection from left to right that decreases suspension stiffness. That's why so many cars add left to right suspension stiffeners. The front to back rigidity is less important than the left to right because it impacts turning. The Coupe's roof beam now provides a solid connection from the left to right of the car making it far stiffer than before.

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It will be interesting to see how that logic plays out with the SCCA and the other sanctioning bodies. Hopefully it will work out in your favor.

Every analysis I have ever seen talks about torsional rigidity being the thing that convertibles lack compared to closed cars, and torsional rigidity is measured across the corners. To increase it requires bridging the cockpit.

The "left to right suspension stiffeners" that I am familiar with are mostly strut bars connecting the tops of McPherson struts, and of course the bars that tie the suspension pickups together like the two offered for the Kappas. Unless it does a better job of bridging the back of the chassis, it doesn't seem like the bodywork will add that much.

Of course its pointless to debate it without data, and that isn't my intention anyway. Again, hopefully it will work out to everyone's benefit.

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John
Lexington, KY
Sky VIN 00252
5-Sp Manual
Midnight Blue

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Just relying on my knowledge of Fiero construction here for a moment…

The Fiero was built using a full space frame underneath the body. Sort of like having a race car (tube frame) chassis underneath. One of the main members in the car for structural rigidity is the hoop that comes up the B pillars and across the roof, behind the passenger compartment. The structure there is so wide that it precluded putting any rear window in the notchback coupe (GT’s had a window farther back in a fastback looking design).

Anyway, on conversion to a convertible, loss of this structural member was very harmful and required a lot of undercar cross bracing, and even the altered chassis was still more jello than robust (and intact, those cars had really good structural rigidity, especially for that era). Conversely, leaving this member in, and removing the side rails running front to back over the passenger compartment for installation of T-tops was not nearly as damaging to structural rigidity. Granted, T-top cars still had a center “T” bar, but it was the most beefy structure you ever saw, and a single connection would still be more susceptible to bending and loss of rigidity compared to a standard cage.

Anyway… long story short, I can believe that the coupe’s roll hoop structure is integral, based on what I know of Fiero construction.

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Brentil,

As far as you know the suspension components should be nearly identical to the 'vert, right? I'm hoping they are because if so the Koni shocks (and other shock/coilover setups) currently available should work on the coupe.

Also, any word on Z0K Coupe timeframe? I have a friend who is ready to get rid of his auto GXP for a NA Z0K. He will hold off if there is a NA Z0K Coupe on the horizon.

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