991 shell twist

[boringbeige]

I have a 991 with the glass 'panoramic' style roof. The shell isn't as stiff as I had expected, there is a bit of twist in it. Having had a bit of a look at how it's constructed it seems to me that the entire roof is a module that is fitted to the car as per the build spec ordered. The fit lines for the glass roof, the metal sunroof and the no-sun-roof roof all look the same. As though the entire roof is fitted the same way, whichever roof you spec. Does this mean that the full metal no-sun-roof roof will bring no additional torsional stiffness because it isn't welded to the body sides, but just clipped or bonded in place like the two sun roof versions? Does anybody know?

[BertBert]

one imagines that it would be perfectly possible in these days of clever glues and techniques to "strongly bond" the roof in? Lotus started gluing their chassis together ages ago.

Not saying this is what they do as I have no idea, but just musing over the possibility.

Bert

[g7jhp]

Sounds a little like the 993 targa, which were based on th 993 convertible, so not as rigid as the coupe.

[Pope]

Compared to the preceding model (997.2) the 991 shell had the following highlights

- Torsional rigidity increased by 25%
- Intrinsic torsional frequency increased by 20% and intrinsic flexural frequency by 13%
- Weight of bodyshell structure reduced by 13%

The roof cassette section is bonded into the roof rails. The roof rails are a similar design to the targa model it succeeded (though targa had bolt-in connection not bonded).

The large glass sections float to allow relative movement during use; the application of a particular grease to the seals of the roof has recently been implemented to reduce noises.

[996TT02]

I can only comment that when the fully removable and hence only clip-on hardtop is fitted to my MX-5 the car is noticeably stiffer.

So a bonded-on roof would (should) be way better.