So.........Ive heard it time and time again. Real racers or hardcore enthusiast love hardtops due to their structural integrity over targa tops, t-tops and some even say Sunroofs.

Example A : The Mark 4 Toyota Supra Twin Turbo. Probaly the most rare, Expensive and sought after Supra is a Twin Turbo MANUAL( no auto) Hard top. Personally , I love the targa top on the Mark 4 Supra and think it is part of what makes the car so sexy but to each there own.

Ive always though that is may be an over rated statement as Manufactures stiffen the chassis on these style cars to compensate. Especially Sunroofs........


Example B. Mazdaspeed 3 never were offered with a sunroof due to there high torque (280ft/lbs) YET the Cobalt SS Turbo with the GM Stage 1 upgrade has 290 ft/lbs of torque. I own a Cobalt SS Turbo and Love the sun roof. This car took the record (when it came out) for the fastest FWD car to run the Nuringburg Ring. GM didnt seem to worry about a Sunroof.....

Example C....... Im reading this months car and driver and they feature the Lambo Aventador Roadster/Targa and they quote

"37% lower stiffness compared to the coupe version even with thicker rocker sections and additional composite materials laid over the drive line tunnel"

So im curious with the Fiero. Does the factory T-top and Sunroof effect the structural integrity of the Fiero based on your experience with driving them "competitively"???


Do guys who stuff V8 or high torque engine into a t-top Fiero or sunroof version worry about twisting the chassis or notice a problem??

My 85 V6 w/o sunroof is solid. The 88 GT w/sunroof creaks a bit when twisting over a steep driveway ramp. Just an observation.

All fiero frames are sunroof "setup", it just matters if you have the hole "cut" into your roof.
Some race sanctioning bodies do not allow glass over your head for safety reasons (some won't allow glass in the door for the similar reasons).

-Dave

[This message has been edited by IFLYR22 (edited 04-17-2013).]

When I was drag racing my Nova, I replaced the glass with lexan, but it was for weight loss more than safety.

quote Originally posted by IFLYR22: All fiero frames are sunroof "setup", it just matters if you have the hole "cut" into your roof.

Yup, this is my understanding. The difference in structure is none, the difference in safety would be broken glass versus fiberglass.

The roof structure adds a great deal of rigidity to the spaceframe, the T-top reduces the stiffness of the spaceframe.

I've never felt a difference between hardtop or sunroof, but every T-top car I've driven felt "flexy", even the old T/A.

As IFLYR22 said, the space frames for all Fiero's came from the factory with the hole for the sunroof in the metal substructure. The only difference between a solid roof car and a sunroof car is whether there is a piece of fiberglass over your head or glass so neither one is stronger than the other:



T-Tops on the other hand significantly weaken the car in torsional and lateral rigidity. That means for example that when you turn a corner, the outside front wheel which takes up much of the weight will cause the frame to bend at that corner. The same thing would happen if you started driving up a ramp with only one of the front wheels, the front end of the car will twist more than the back of the car compared to one without the T-Tops.

To explain why, if you imagine a cube made of a wire frame where the bottom wires of the cube represent the rockers and lower cross members of the car, the vertical wires represent the the door posts, A-pillars, and B pillars, and the top wires represent the roof rails, windshield header and the rear roof crossmember, then it's not hard to see why a T-Top is weaker. To make a T-top, you replace the two roof rails with a single new member connecting the middle of the windshield header to the middle of the rear roof cross member. The top corners of the car are no longer supported by three structural members at 90 degrees to each other (effectively triangulating the corner), but rather by only two. In longitudinal bending, where you try to fold the front of the car on top of the rear, it's about the same strength. In lateral bending where you try to fold the car sideways, it's obviously significantly weaker because while the rockers will resist the bending at the bottom, only a single member does so at the top. Finally, in torsional bending where you try to bend the car diagonally, the lack of two roof rails makes a big difference.

So what does it matter if your car bends? The suspension can't do it's job as well keeping the wheels pointed where you want them when the frame is contorting over bumps and in corners. It also means that gaps between body panels have to be a little larger to allow the larger relative movement between them without rubbing.

(edit to add photo)

[This message has been edited by Bloozberry (edited 04-17-2013).]

My 88 race car with sunroof is just a solid as my son's 88 race car without the sunroof.

so is it safe to say that sunroofs on all "Performance" cars make zero difference compared to their Hard Top variants?

Or is does this just applies to Pontiac Fieros?

quote Originally posted by HydroFiero: so is it safe to say that sunroofs on all "Performance" cars make zero difference compared to their Hard Top variants? Or is does this just applies to Pontiac Fieros?

Not in all cases. The fiero is one of the few vehicles to have a "pre cut" hole in the roof from factory. Then again not many cars had the option to remove every panel lol
Based on that alone it makes the fiero one of the best hobby cars out there especially since if you have a notchie then with little modification you can have a fastback.

Just to Fieros since the outer skin plays no role in the structural strength of the car.

the C&C Ttop in my 88 seems pretty sturdy, i never got the sense the body was warping around it