Simply REMOVING the sunroof

[UofACATS]

Does the oem sunroof assembly provides any torsional support to the vehicle?

If I were to pull it and drive with the gaping hole, would chassis flex actually worsen?



*This will get plugged when the cage goes in, and is a garaged, track only toy.

 

[matthewdesigns]

I am going to go out on a limb here and say very little structural rigidity is added if any at all. Without the glass, the frame itself is essentially just a big rectangular donut bolted to the roof, with no connection to the A or B pillars to tie things together. And the glass certainly isn't going to be a stressed member.

There is a complementary frame of sorts to which the sunroof assembly bolts, and it is glued/welded to the inside of the roof skin, so that if anything would probably do the work of offsetting the localized loss of strength due to the hole in the roof. I've never seen inside the headliner of a non-sunroof car to say whether or not it has the same bracing, but I'd think if it's there it's probably just to keep the roof itself supported as in the sunroof cars.

 

[UofACATS]

It's out. It's essentially (7) 10mm nuts to remove/install it.

Frame with the glass included, motor, and the nuts to keep it in place weigh 27.5lbs on my scale (0.5 increments). This doesn't include the wires to the assembly, the 4 drain tubes, or the sunroof sliding cover.

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[matthewdesigns]

Yeah, I've done that more times than I'd like to recall, in multiple efforts to repair mine. Glad you got it out, and thanks for the weight...that's something I never did.

 

[xloki77x]

This was on the Link forums...

...Modern cars are stressed skin monocoques, a high degree of their stiffness is derived fro the skin. Because the body already has several large holes cut in it, the roof is a significant player in routing the stresses through the shell - this is why drop head designs have large sills and centre tunnel, that replaces the roof's function - it's also why cars that were not designed to be drop heads gain as much as 100lbs over the weight of the roofed car, as masses of stiffening has to be added to stop the car from pretzeling.

Compounding the issue is that most if not all sunroofs are rectangular in shape - the weakest possible shape to employ. by have 4 sides, the shape is free to lozenge under the lightest loads. Were the sunroof circular or triangular it would be much stiffer, but it's not. There's many chassis design books floating around, one of my favourites is from the late 60's/early 70 by a F1-type designer, Len Terry, and a technical editor, Alan Baker, as it details the logical transition from spaceframes to monocoques - and perfectly captures what we're discussing here. It's called Racing Car Design and Development. There are plenty of others though - anything by Allan Stanniforth will do and one of Carrol Smith's books will cover it too, no doubt.

Getting rid of the sunroof still won't stop the front clip from flopping around like a dying fish though

 

[dsm-onster]

Not sure the weight savings would be worth the wind drag losses . But I pull off the glass all the time an drive around in the summer. It's the closest thing to targa I'm willing to take the time to do to the car.

 

[UofACATS]

This was on the Link forums...

I've read that. What specifically are you referring to? Thank you.

It's also part of why the sunroof is out of the car. That problem is going to be fixed.

Not sure the weight savings would be worth the wind drag losses .

Right. I actually edited my original post which was long and rambling about the excessive wind, but then decided simpler was better.

On track, I run with the windows down to point-by, and realize opening another massive hole isn't helping. I wonder whether the drag will be worse than the open windows given the location on top of the vehicle instead of the sides.

I can bring it to the track and do a couple laps both ways though.

 

[xloki77x]

When road racing, most sanctioning bodies will require your windows be down and your sunroof closed or plugged for safety reasons. Like the excerpt above mentions, the best thing you can do is plug it and weld it.

Torsional stiffness will increase dramatically with the installation of a roll cage and welding something in place of the sunroof will further enhance that modification. And to do the cage properly, you'll have to take the roof off anyway so why not get a non sunroofed roof and swap them out?!

Pete

 

[UofACATS]

When road racing, most sanctioning bodies will require your windows be down and your sunroof closed or plugged for safety reasons. Like the excerpt above mentions, the best thing you can do is plug it and weld it.

Torsional stiffness will increase dramatically with the installation of a roll cage and welding something in place of the sunroof will further enhance that modification. And to do the cage properly, you'll have to take the roof off anyway so why not get a non sunroofed roof and swap them out?!

Pete

Gotcha. (jealous of your car btw There will be a cage and plug. I am going to ask the fabricator to secure the plug to the roof either by welding, bolting to the oem sunroof attachment points, or both. Maybe weld/bolt it in and attach it to the cage making the entire car and skin solid. Just dreaming here.. I know some builders drop the cage through the floor instead of pulling the roof off, but I'm not that far yet with my cage. If the roof is coming off, a non-sunroof version is going on no question about it. I simply do not like sunroofs in any type of performance car. I liked the one in my LS400, but that's it.

Quick link to a sample cage with a pretty cool seat mount (I plan to have done as well.)1997 Boxster Spec Cage - PRECISION CHASSIS WORKS

I'll mention the sunroof where I run and see what they say. Thank you for the feedback.

 

[xloki77x]

Man, that cage is sick. Those guys are good at what they do. I would say integrating the plug into the cage design would be a good thing. Just make sure the plug is as flush as possible so as not to disturb the airflow going over the roof (i.e. get rid of the lip on the forward side of the sunroof if there is one). The cage should take care of most of your chassis flex so the sunroof hole

Thanks for the kind words about my car. The roof is actually off at the moment for some reworking of the cage...non sunroofed of course.