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JMortensen

Jon's 2 year roll cage saga...

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I've looked at quite a few different designs for roll bars and cages now, and I have a question or two.

 

I intend to do a 4 point bar with the two supports attaching to the strut towers. My question is this: Is it better to attach the supports to the TOP of the main hoop, or to the SIDES of the hoop, or does it even matter at all? I've seen em both ways, just wondering if one has an advantage over the other.

 

It seems to me that it would be a lot easier to weld everything if the supports went to the sides of the hoop instead of the top. It could be easily welded inside the car by popping out the quarter windows. If it needs to be on top then it's a little trickier. I've seen 3 solutions, and if anyone has any feedback on these that would be appreciated too.

1. Cut holes in floor with hole saw, slide hoop down into holes, weld the supports, lift back up, slide plate over hole and under bar, weld bar to plate and plate to floor. This was a method used for cages, not bars, might not apply to what I'm doing.

2. Cut hole in roof, weld bar, weld patch in roof.

3. Tack everything, take out of car, weld, put back in car. I guess sometimes this is pretty difficult to do depending on the design of the bar. I think this would be pretty easy to do on mine, especially since the car has no interior right now.

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OK I think I might have figured out part of the answer. If you brace on the sides then the brace is way out wide on the bar, and when you tie that into the strut tower, the bar will either have to be angled inwards quite a ways, or will have to tie to the top of the strut tower to be straight. Is there any problem with it being angled? Seems like that would make it weaker in case of a rollover.

 

I did already weld a tube between the strut towers, would like the braces for the main hoop to attach near that other tube if possible.

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Nobody has anything on this for me? I did see a roll bar in a pickup truck today where these supports were clearly angled. Not sure how pickup roll bar relates to car roll bar...

 

Some of us are burried at work and can't find the time to play as much as we might like. Another goup are probably headed to Shasta :-)

 

Is this going to be weld in or bolt in? I'm guessing bolt in. Does it need to be SCCA legal? I seem to recall you could only have a max of 180 gegrees of bend in the main hoop. It may not work to put holes in the floor and drop the bar down to weld the top. In this case I think You'll need to build up a base from the rocker to the raised section in the rear floor that fits under the bar.

 

I think the SCCA has a rule regarding how much angle the rear stays can have from the car centerline. I don't have a rulebook handy to say for sure. So I would check that. If they don't I think you're fine connecting to the crossbar you have welded in the back. There are a host of solutions from here. I think you'll need a diagonal from the drivers side top of hoop down to the lower passenger side at minum.

 

To make is stiffer you can put in a upper and lower X to the opposing struts. I'd also look at attaching to the roof section if this is weld in. This not only makes the structure stiffer but will help to keep the car together in a side impace. The lower X requires some creativity to get around the seat depending on how far back yours is.

 

If you intend a bolt in solution that I have another idea for you.

 

Sorry, work calls --

 

Cary

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Some of us are burried at work and can't find the time to play as much as we might like. Another goup are probably headed to Shasta :-)

Oh yeah. Forgot about that.

 

Is this going to be weld in or bolt in? I'm guessing bolt in. Does it need to be SCCA legal? I seem to recall you could only have a max of 180 gegrees of bend in the main hoop. It may not work to put holes in the floor and drop the bar down to weld the top. In this case I think You'll need to build up a base from the rocker to the raised section in the rear floor that fits under the bar.

Weld in. I've got the hoop covered. 4 bends, 180º. That part I'm not worried about. I think I'm just going to plan on making some platforms to set the hoop on and weld to it there. I like John Coffey's bar that he did for a customer. He scooted the front legs of the hoop forward then leaned the whole hoop back so that there is more seat clearance. Plus I am going to get a 10º layback seat, so I think I'll do OK on seat clearance.

 

I think the SCCA has a rule regarding how much angle the rear stays can have from the car centerline. I don't have a rulebook handy to say for sure. So I would check that. If they don't I think you're fine connecting to the crossbar you have welded in the back. There are a host of solutions from here. I think you'll need a diagonal from the drivers side top of hoop down to the lower passenger side at minum.

That's the type of info I guess I need. I'm not going to be racing with SCCA most likely though. I guess I should check with NASA. This is going to stay an autox/track day car for a while, but I'd like to build something that I can use later on if and when I do decide to do some door to door stuff. Maybe I should just build what I want then screw with it later if some sanctioning body says it's not appropriate. Diagonal crossbar and horizontal brace are also part of the plan, BTW.

 

To make is stiffer you can put in a upper and lower X to the opposing struts. I'd also look at attaching to the roof section if this is weld in. This not only makes the structure stiffer but will help to keep the car together in a side impace. The lower X requires some creativity to get around the seat depending on how far back yours is.

Definitely planning on attaching to the roof and sides, not planning on an X just due to the extra weight.

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Top is better especially if you're going to weld a tab to the roof support near the hatch hinge mounting area. SCCA allows the rear braces no lower then 6 inches from the top of the top of the main hoop and at an included angle of no less then 30 degrees. I tacked the rear supports to the main hoop in the car and then welded outside the car.

 

The reason I mounted the bottoms of the main hoop to the boxes I built was to ensure roll over loads went as perpendicular into the plating and main hoop as possible. In a roll over I wanted to reduce sheer loads on the tubing and welds.

 

You will also either need a diagonal brace in the main hoop (SCCA/NASA rules) or an X brace in the rear braces (FIA rules).

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Thanks John. The more I look at it the more I like your design over all the others I've seen. Any idea how straight the supports have to be? I suppose if I weld to the top they can be pretty damn straight, just curious if there is a rule.

 

BTW for anyone else looking at NASA's rules pretty much says "refer to SCCA's rules".

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I made my cage in sections. The main hoop, the bars from the top and sides of the main hoop, and the rear strut bar were a complete subassembly. To make the main hoop subassembly, I tacked everything together inside the car and then removed it for final welding on the bench.

 

A benefit to this was that I could paint the cage and interior before installing it. This picture shows the rollbar after painting but before final welding. The entire assmbly could be removed by tipping it forward and wrapping it out.

 

PICT0003.JPG

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Any idea how straight the supports have to be? I suppose if I weld to the top they can be pretty damn straight, just curious if there is a rule.

 

No rule but the straighter the better. One less thing for the tech guys to worry about.

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I made my cage in sections. The main hoop' date=' the bars from the top and sides of the main hoop, and the rear strut bar were a complete subassembly. To make the main hoop subassembly, I tacked everything together inside the car and then removed it for final welding on the bench.

 

A benefit to this was that I could paint the cage and interior before installing it. This picture shows the rollbar after painting but before final welding. The entire assmbly could be removed by tipping it forward and wrapping it out.

 

[img']http://album.hybridz.org/data/500/medium/PICT0003.JPG[/img]

I looked long and hard at that picture, but I have already welded in my strut bar and it is .095 wall based on John's and Drax's previous suggestion in a long ago post. Maybe that doesn't matter, but it seems strange to use .120 and then attach it to .095.

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Personally, I think the rear braces at .095 are plenty strong. But, SCCA mandates that the rear braces be the same wall thickness as the main hoop so that requires .120 wall for almost all of our 240Zs. I personally wouldn't be worried about attaching the .120 wall rear braces to an .095 strut tower bar as long as they were very, very close to the strut towers.

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Personally, I think the rear braces at .095 are plenty strong. But, SCCA mandates that the rear braces be the same wall thickness as the main hoop so that requires .120 wall for almost all of our 240Zs. I personally wouldn't be worried about attaching the .120 wall rear braces to an .095 strut tower bar as long as they were very, very close to the strut towers.

OK, so is there a reason why you attached to the tower rather than the bar on that roll bar you did? Is there another advantage to one over the other?

 

I can see one advantage as far as installation in that it would be easier just to notch the tube on each end and weld it than to make a plate and weld the plate to the tower then weld the tube to the plate.

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My strut bar and the two tubes connecting the main hoop to the strut bar are 1.625 x 0.083. The main hoop, the diagonal, and the bars from the top of the main hoop to the strut bar are 1.625 x 0.120. All of the tubing is 4130N (normalized chromoloy) and is TIG welded.

 

My door bars are 1.625 x 0.120, the hoop at the firewall is 1.625 x 0.083, and most of the front end tubing is 1.625 x 0.065.

 

My subframe is 2.5" square x 0.085 mild steel.

 

All of the tube not specifically designated in this picture are 1.625 x 0.065

 

FrontEnd.jpg

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A personal preference. Bars attaching to other bars are done to transfer load within the roll bar or cage structure. Ultimately the load being transferred has to go to the vehicle somewhere and the more places it can be spread around the better. I would rather have bars attaching to vehicle structure if at all possible. But, sometimes rules get in the way: SCCA mandates 8 points of attachment to the vehicle for IT cages.

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I can see one advantage as far as installation in that it would be easier just to notch the tube on each end and weld it than to make a plate and weld the plate to the tower then weld the tube to the plate.

 

If you measure the car you'll find it will generally be stiffer if you spread the load out on the strut tower. It is easier to go to the tube but you can't spread the load out as much and this seems to make the structure less stiff.

 

But then again, you have the rules to deal with. On a couple of my cars I haven't worried about the rules I welded a plate across the ribs top pf the tower and brough the down tube into this. Then the side tubes I brought into the front face of the rear tower. And then had a strut bar that was welded across the towers.

 

I did something similar on my mod car after playing around with whether it was better to run the tubes together or spread the load out. Those simple experiements indicated that it would be better to spread the load.

 

Hope this makes sense,

 

Cary

 

Cary

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If you measure the car you'll find it will generally be stiffer if you spread the load out on the strut tower. It is easier to go to the tube but you can't spread the load out as much and this seems to make the structure less stiff.

 

But then again' date=' you have the rules to deal with. On a couple of my cars I haven't worried about the rules I welded a plate across the ribs top pf the tower and brough the down tube into this. Then the side tubes I brought into the front face of the rear tower. And then had a strut bar that was welded across the towers.

 

I did something similar on my mod car after playing around with whether it was better to run the tubes together or spread the load out. Those simple experiements indicated that it would be better to spread the load.[/quote']

Yeah, I think I got it. Basically you ran both a bar from the side to the trapezoidal area outside of the strut tower and another bar from the top to the strut tower itself. That seems like it would have been plenty stiff.

 

Still mulling it all over but this is really helping a lot. Thanks guys.

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Mine has been good in use, no diagonals that interfere with rear view, helps stop stuff in the back sliding forward, unobtrusive and its stiffening effect definately made a difference to the way the car drives. The extra mounting point at the rear juncture of the transmission tunnel provides additional support for the hoop at the crucial top bends.

 

Excuse my raving, its just that it is about the first thing on the car that has turned out better than hoped for :)

 

showphoto.php?photo=3122&cat=500&page=1

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Got my main hoop last night. Looks good, fits TIGHT. Really really tight. I'm going to do something a little different to mount it, the boxes are basically going to be upside down and the bar will attach to the vertical part of the rockers. Based on his ITS cage article, I think katman will approve when it's done.

 

Now need to get my *** in gear. Still haven't mounted the seat. Need to get the seat mounted, the cage finished and the suspension in so that I can roll the car out, pull the engine/trans, back the car into the garage and put it on the rotisserie that I haven't made yet... Don't know how far I'll get, but those are the goals.

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Went out to see about fitting the seat. Kinda surprised at what I found.

 

I started by setting my Recaro tracks on the stock seat mounts and then setting the Ultra Shield seat on top of the old tracks. It seems like the seat is WAY too high, but that’s weird because the padding in the butt is only about 1†thick. But even at that my hair is brushing against the headliner. I did have a couple pieces of 1x4 wood in there so that added 3/4 inch to the height of the seat, but I’m really surprised that I’d need to go lower.

 

It looks like I’m going to need to completely remove the stock seat mounts and start over because they are too high. I've got some square 1" x .065 tubing that I can use to build a frame. I guess I can weld it to the rockers and the trans tunnel then maybe put a support underneath on each side to the floor.

 

Do I sound like I'm on the right track here? Anyone know of an easier way? Pics of seat mounts would be GREATLY appreciated...

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It looks like I’m going to need to completely remove the stock seat mounts and start over because they are too high. I've got some square 1" x .065 tubing that I can use to build a frame. I guess I can weld it to the rockers and the trans tunnel then maybe put a support underneath on each side to the floor.

 

Do I sound like I'm on the right track here? Anyone know of an easier way? Pics of seat mounts would be GREATLY appreciated...

 

I suggest you remove the adjustable tracks and set the seat up for yourself. But, most folks don't want to do that...

 

Take your 1" square tubing and cut one side off so its a U-channel. Contour the open end so it fits tight down on the floorpan and connects to the rocker and the tunnel while keeping the top surface sqaure and level side-to-side. Stich weld the U-channel to the floor pan, rocker, and tunnel. Drill holes in the top big enough to get a 3/8" nut through the opening. Weld a 3/8" nut to a 1/2" washer, insert the assembly nut down into the hole, and weld the washer to the top of the 1" tubing.

 

Tip: Order 3/8" four corner weld nuts from McMaster-Carr and 1/2" uncoated metal washers.

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I suggest you remove the adjustable tracks and set the seat up for yourself. But, most folks don't want to do that...

My wife actually races the car every once in a great while. I'd like to keep it so that she could drive when she wanted. It's really hard to get her out there, but she LOVES it when she goes. She actually spun the car at Buttonwillow once. I was so proud... :)

 

Take your 1" square tubing and cut one side off so its a U-channel. Contour the open end so it fits tight down on the floorpan and connects to the rocker and the tunnel while keeping the top surface sqaure and level side-to-side. Stich weld the U-channel to the floor pan' date=' rocker, and tunnel. Drill holes in the top big enough to get a 3/8" nut through the opening. Weld a 3/8" nut to a 1/2" washer, insert the assembly nut down into the hole, and weld the washer to the top of the 1" tubing.

 

Tip: Order 3/8" four corner weld nuts from McMaster-Carr and 1/2" uncoated metal washers.[/quote']

So mount the seat an inch off the floor? That's going to be LOW. I guess that's good for center of gravity. How about not cutting the tubing into a U, but instead cutting the floor where the bump is in the middle then welding that part from the bottom?

 

Good tip BTW, I like that way of securing a nut inside the frame rail.

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but instead cutting the floor where the bump is in the middle then welding that part from the bottom?

 

Don't cut the floor. What you're building is a box with the floor as one side. Look at how the factory seat mount is built and you'll see that they went to great effort to keep from cutting the floor.

 

What would be even better would be to build a U-shaped channel with flanges that have holes punched in them for spot welding to the floor. The edge of the flange can be stich welded and the flange holes can be filled as spot welds.

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Why can't I just stitch the tube to the floor? I guess I'm not getting the importance of not cutting the floor, especially if it gets welded back to the tube.

 

Had a little brainstorm after your first response though. I "unwelded" my recaro sliders and I think I can use them. They have a piece at each end that bends down that has 3 height adjusting holes in it. So I figure I can weld a piece of the square tube to the floor and trans tunnel at the proper spacing to use the old sliders. Then I can weld the appropriate nuts into the tubing using your previously described method. It will still call for the tubing to be a bit off the ground though, probably 1/2" or so. I understand what you mean about attaching the bracket to the floor all the way across. I do have a bunch of sheet metal. Wondering if I couldn't weld that to the square tube and to the floor across to spread the load along the floor...

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