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T-top brace bar.

Old 03-01-2019, 11:52 AM
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T-top brace bar.

To start, I've got an 89 bird with T-tops. Chassis stiffening is on the books right now.

The one thing I am not doing is converting it to hard-top. I think T-tops are the $hit and I almost never drive with them installed.
I've done some searching, and I can't seem to find out if there is any potential improvement for the T-top roof. Will I see any improvement if I build additional bracing in the structure of the roof? Would a set of bars running across the gap at the edge of the roof-line add any useful rigidity?


My idea is to add some bracing up the Pillars with 1/2" square tubing and additional spot welds on the seams, build additional bracing from there along the width of the roof and then as far out as possible under the middle bar. This is the blue lines. The yellow lines would be a removable set of brace bars as close to the edge as possible without getting in the way of the T-tops. My goal is roof stiffness, or at the very least a cool set of grab handles. Has anyone done something similar?
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Old 03-01-2019, 12:17 PM
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Re: T-top brace bar.

Cheapest and easiest is to start with Sub Frame Connectors. That, in itself will add rigidity.
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Old 03-01-2019, 01:57 PM
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Re: T-top brace bar.

I already have a set of Heidts inner, and an outer set I made. I'm just wondering if this will give more support on an extra plane, since the sfc's are all down under the floor and a stiffer roof would make more of an A-frame structure of the car.
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Old 03-01-2019, 03:04 PM
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Re: T-top brace bar.

IMO this will not get you what you are looking for. Unless you can triangulate your additions, you will just be adding weight, up at the top of the car where you don't want it. When you apply force to the parts of the car that are in contact with the road, the majority of the flexing happens along the longitudinal axis of the car, your brace will just be flexing with the rest of the car. If you have a good (one that triangulates) strut tower brace, you will be way further ahead. If you feel you must add support to the rear of the car, consider a main hoop with supports to the rear upper shock mounts, and has a good cross brace.


ps: 1/2 square tube is not the best choice either, IMO....
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Old 03-01-2019, 10:12 PM
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Re: T-top brace bar.

So the one direction this would add support is the least necessary. That is very helpful.
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Old 03-06-2019, 05:09 AM
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Re: T-top brace bar.

Originally Posted by Firebirdwade View Post
To start, I've got an 89 bird with T-tops. Chassis stiffening is on the books right now.

The one thing I am not doing is converting it to hard-top. I think T-tops are the $hit and I almost never drive with them installed.
I've done some searching, and I can't seem to find out if there is any potential improvement for the T-top roof. Will I see any improvement if I build additional bracing in the structure of the roof? Would a set of bars running across the gap at the edge of the roof-line add any useful rigidity?


My idea is to add some bracing up the Pillars with 1/2" square tubing and additional spot welds on the seams, build additional bracing from there along the width of the roof and then as far out as possible under the middle bar. This is the blue lines. The yellow lines would be a removable set of brace bars as close to the edge as possible without getting in the way of the T-tops. My goal is roof stiffness, or at the very least a cool set of grab handles. Has anyone done something similar?
Huh, interesting idea... it makes me wonder if you pulled the headliner if you could find room to weld in maybe some 1" tube the whole way around the perimeter of the t-top opening without losing much headroom. I've also had the thought of doing something like this with a rollcage, running 2 bars down the middle instead of around the outside.

How tall are you? My biggest concern is that you're going to end up with this stuff invading your head room making for a dangerous situation in a side impact. I'm 6'4" and I typically lower my seats (I've had a hardtop car and 3 t-top cars, the hard top I couldn't sit in with a helmet without lowering the seat, and the t-top cars typically I would smack the roof pannels in a bump), and I was once in an accident where I was t-boned and put my head into the bar between the t-tops and even that ended up giving me a concussion.

Originally Posted by 427seven View Post
IMO this will not get you what you are looking for. Unless you can triangulate your additions, you will just be adding weight, up at the top of the car where you don't want it. When you apply force to the parts of the car that are in contact with the road, the majority of the flexing happens along the longitudinal axis of the car, your brace will just be flexing with the rest of the car. If you have a good (one that triangulates) strut tower brace, you will be way further ahead. If you feel you must add support to the rear of the car, consider a main hoop with supports to the rear upper shock mounts, and has a good cross brace.


ps: 1/2 square tube is not the best choice either, IMO....
Triangulating will make it stronger and you don't want to add weight anywhere, but the roof is exactly where you want to add rigidity. It's easy to add a lot of structure to the bottom/floorplan of a car, where just a little bit of structure added to the roofline will make a great big difference in rigidity (the farther the structure is apart the more rigidity it will add. The only reason that subframe connectors are the popular way of stiffening a chassis is that they are a way you can do it easily without messing up the look of the car.
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Old 03-06-2019, 09:24 AM
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Re: T-top brace bar.

Thanks for the input,
I've got the interior out, with an abs headliner and some clever routing, I think it could happen. I'm not too concerned with headroom if I do this, or a roll cage since I'm 5'8.
My goal is of course a roof that is at least as stiff as a hardtop. With ~1" round tubing, The roof would essentially be three rectangles, and if properly supported by the pillars, I'm curious as to what types of flex can I fight.
My thoughts: (none of these are my car)

It would certainly help with flex like this, where the roof is under compression. This is what I was picturing initially.

This is what I'm picturing as far as torsional forces of the body. Cornering for example. If I've got this right, then an X shape in the roof would be ideal to channel the force to the opposite side of the car and keep the roof in square. I can't keep T-tops with an X shape, so I would need to use the rectangle approach, but that should still be better that an open H shape(factory T-tops).
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Old 03-06-2019, 09:41 AM
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Re: T-top brace bar.

IMO I think you might be overthinking this. Rather than stiffen up the T-Top area, you would want to just redirect that stress away from the T-Top area during hard cornering, or severe sixty foot. Normally a three point strut tower brace, along with welded in sub frame connectors will take care of the issue. You can also ad a roll bar (no need for the full cage), just a two point roll bar tucked behind the T-Top opening for additional strength to be used with the STB and SFC's, you won't need to worry. Hell, even without the roll bar I wouldn't worry with just the STB and SFC's. I'd be more concerned with securing the T-Tops to their latch lol...

- Rob
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Old 03-06-2019, 10:43 AM
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Re: T-top brace bar.

Too much is made of the "weakness" created by the addition of t tops, but the only reason a hole in the roof is significant is bc the chassis is inadequate to begin with. You have to address the underlying issue. Arguably the roof isn't needed at all for a rigid chassis, many race cars prove that (even top fuel cars don't have a roof). With our cars, if you want to have a t top or not, you have to work with the chassis. Rob's comment re-enforces my original suggestion, and I have attached a diagram from Herb Adam's "Chassis Engineering". Look closely at fig 12-13 and 12-14, in both diagrams the "car" has a sheer plate (like the roof inn your car) but the strength difference is from triangulating support off the front and rear suspension points. It would, in fact, be the same if there were no roof at all.


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Old 03-06-2019, 10:51 AM
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Re: T-top brace bar.





Just in case you want to experiment with square v triangle....
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Old 03-06-2019, 11:13 PM
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Re: T-top brace bar.

My car is a t-top but it also has a full cage in it and isn't street legal. I've never lost a t-top going down the track.

Good weld in SFC stiffen up the chassis on even a daily driver street car. Adding an anti-roll bar to the rear suspension will keep the chassis from twisting under acceleration even more.
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Old 03-07-2019, 03:11 PM
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Re: T-top brace bar.

I saved these pictures from here on the forum a few years back. These are the braces Cars and Concepts added to the roof of an F-body when they cut it to add t-tops.








Being thin, they should take up close to zero headroom, and they should not weight too much. But they would indeed add weight, and at the worst possible place height-wise.

While I would not expect these to do a measurable amount of good for whole chassis torsional rigidity, I had thought if I stumbled across some in a bone yard, that I might think about adding them to make the roof more stable, and perhaps reduce a t-top squeak or two. And God forbid a roll-over, they might add a modicum of extra strength.

But I suspect sub-frame connectors would provide a far greater bang for the buck at stopping these noises, as well as adding a lot of help everywhere else.
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Old 03-07-2019, 08:13 PM
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Re: T-top brace bar.

Those braces look like they're just to prevent the body from cracking if there's any twisting.

Better than nothing I guess and better than the tubular bars already suggested.
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Old 04-11-2019, 02:34 PM
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Re: T-top brace bar.

What about door bars something like (Miata in this case) this in addition to your current subframe connectors? Basically tying close to the same points together(as SFC) but on a different plane??

https://trackdogracing.com/hd-doorbars.aspx
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Old 04-11-2019, 03:52 PM
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Re: T-top brace bar.

That looks to function on the same principle as the door bars on a six point cage.. I didn't know anyone put standalone door bars in, I wonder if there is enough structure in the jambs of these cars to see an improvement.

Here is the 4 pt bar I put in
I may just have to make a set of door bars if my current setup doesn't satisfy me.
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Old 04-12-2019, 11:04 AM
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Re: T-top brace bar.

two pieces isnt enough to stop the twisting motion, you'd have to build pretty much an exo-skeleton brace. it would have to be your two pieces, then have additional pieces to come up and over the t-bar. probably would be adding a decent amount of weight (unless you know someone who can weld and bend aluminum tubing) but i like the concept idea of that you could take it off when youre not racing tho. if it were me though, i'd prob just do STB and a similar brace in the rear inside the hatch.
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Old 04-18-2019, 06:36 PM
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Re: T-top brace bar.

The guys here in Tallahassee, building new Trans Ams are making T-Top cars from the new 6th gen fbodys. They insert a thick chunk of billet aluminum, wrapped in carbon-fiber, in the altered roof.....of course I suppose these new bodys are pretty ridgid to begin with (compared to a third gen).
The end result is nearly $100k or more, but they are built to handle the 1000hp LS.

-Rich
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