Cages - Experiences wanted

[rturbo 930]

Yeah, I'm looking at your rear bars, it looks like the mount somewhere in the trunk? I'm also looking at where your main hoop mounts. It's hard to see, but it looks like it could go back a little more, is that right? I'm also thinking it could be leaned back a bit. My plan was to put it pretty tight up to the wheel wells, leaving just enough to get the thing welded, and also put vinyl on the wheel wells - maybe an inch or so out. Though, I'd also consider cutting the wheel wells, and running the bar into them. If I do a bar, I'll likely do it to SCCA rules, so I'll have to double check to make sure this is all in line with their rules. My car is going to be primarily a street car, so it's important that the roll bar doesn't get in the way of that.

[EF Ian]

2 hours ago, seattlejester said:

My bars are pretty visible given mine are painted white, my insurance agent and company didn't comment on them, they were more interested in making sure the panels were more or less in good shape.

I am with a specialist insurance company due to the mods. I actually had to renew it the other day (nearly £800 ) so I took the opportunity to check if it would be an issue, for them it was't and wouldn't cost any more since my car is already super heavily modified.

 

 

 

 

2 hours ago, seattlejester said:

I think the way a roll bar is doesn't add too much stiffness unless you weld it to the roof like JMortenson says. I have subframe connectors, welded in strut bar, and a roll bar and the hatch still doesn't want to close straight if I park off camber

I don't see it like that, you are connecting the two suspension towers, connecting the towers to the rocker panels which provide a lot of the strength for the car and also providing a fairy rigid bar connecting the two rockers together and then theres a bar coming off the top of the towers whihc must help somewhat to provide some vertical stiffness for the towers upward against upwards forces. I would consider connecting it to the roof as I can use some plate in the middle and still run the trim as I would just need to trim a section out the plastic to allow it to fit.

 

My front is as reinforced as I can make a road car so I'm no longer worried there. Honestly my front end feels solid and no creaking or any visible flex no matter where I jack it up.

 

 

 

 

Heres the cage I have in mind (just imagine all the lines are where they should be as I couldn't get it perfect in paint) I plan to have the main hoop uprights part recessed into the well. With this design I reckon I can still run my stock belts. The bars in yellow are optional if they are thought to be needed. I do realise that without a diagonal in the main hoop I am loosing strength but I don't want to sacrifice the room and its not like I am racing in any competitions plus I'm sure even without I'm still going to be much safer than with no cage.

 

 

 

1 hour ago, rturbo 930 said:

I take it you plan to run 3pt seat belts on the street? And I believe you have a '78, with seat belt reels on both the strut tower and on the floor, yes? If so, this is going to be harder than you think.

Correct in both cases. But I think the cage above will be solid and still let me run my stock belts. Of course I am not a cage designer so it could be deeply flawed. I guess modern belts mounted to a small floor reel with the upper mount mounted to the cage would work.

 

 

 

 

Other ideas for fun, tell me what you think.

 

 

 

 

 

 

 

 

 

 

 

With no cage what is better, x on its own, bar on its own or both like below or is both not adding much other than weight?

 

Edited March 28, 2018 by EF Ian

[seattlejester]

Yea, I make no qualms, my bar is not very good. They mount to a piece of 2x2 welded into the trunk. I should revisit it with some revisions, I've also contemplated just removing it altogether.

 

The bar is sitting on a centered  3x3 plate if I remember so it could move maybe an inch or so back I think, but it is pretty tight, I think as you mention the only way to get tighter is to cut into the rear wheel wells which I have seen, but welding in the bigger tube around it and getting the weld at the bottom would probably be quite the task. I don't think you can lean it back without shortening the height quite a bit, I don't have a map light, but I think this sits right in front of where the roof reinforcement is where the light monuts. At the height it is at, if the seat could recline I could sit under the bar with my helmet on. Any shorter and the bar would have to be leaned back even further if you didn't want to risk helmet contact.

 

I think my bars thickness is SCCA, but it has a bend on the "legs" and is a bolt in, bolt together type cage so pretty sure it doesn't meet any requirement there. Yea my car is not a very good street car and it gets driven pretty infrequently. I will admit it is kind of nice having the harnesses and the roll bar in because it makes it a bit more of an event getting in, visually it looks pretty nice, and if I rolled over I think it would keep the roof up, if I got rear ended though I feel like it would possibly just roll forward given where the rear legs mount.

[seattlejester]

If you tie in the suspension towers than a half cage would make a difference, although at that point a triangulated strut brace like PDK or I think even now TTT sells would be pretty effective pretty much similar to the last one you have. I'm not sure there would be an additional benefit, granted I guess you could argue you are tying it to a wider leverage arm in the chassis if it flexes at the bulkhead like rturbo says.

 

I've got some heavy duty subframe connectors and I still feel like the car likes to do the twist, I guess I have never been in the car without them though, so my standard might just be really off or based off of modern unibody structures.

[rturbo 930]

I could be wrong here, but I think the idea is to sort of triangulate from the floor, to the roof, to the rear strut towers.

2 minutes ago, seattlejester said:

Yea, I make no qualms, my bar is not very good. They mount to a piece of 2x2 welded into the trunk. I should revisit it with some revisions, I've also contemplated just removing it altogether.

 

The bar is sitting on a centered  3x3 plate if I remember so it could move maybe an inch or so back I think, but it is pretty tight, I think as you mention the only way to get tighter is to cut into the rear wheel wells which I have seen, but welding in the bigger tube around it and getting the weld at the bottom would probably be quite the task. I don't think you can lean it back without shortening the height quite a bit, I don't have a map light, but I think this sits right in front of where the roof reinforcement is where the light monuts. At the height it is at, if the seat could recline I could sit under the bar with my helmet on. Any shorter and the bar would have to be leaned back even further if you didn't want to risk helmet contact.

 

I think my bars thickness is SCCA, but it has a bend on the "legs" and is a bolt in, bolt together type cage so pretty sure it doesn't meet any requirement there. Yea my car is not a very good street car and it gets driven pretty infrequently. I will admit it is kind of nice having the harnesses and the roll bar in because it makes it a bit more of an event getting in, visually it looks pretty nice, and if I rolled over I think it would keep the roof up, if I got rear ended though I feel like it would possibly just roll forward given where the rear legs mount.

Yeah, I'm by no means an expert, but I think your thoughts there are about right. Easy for to say since I don't have to pay for the replacement, but I think I'd toss it and get a proper one welded in by a good shop.

[tim.d]

1 hour ago, EF Ian said:

 

 

 

Very curious about what the smart people here think about this design.  I'm planning on going down a similar path, also with the main hoop also protruding into the wheel wells slightly.  I've got full length box frame rails that the hoop would brace down into as well.

[seattlejester]

The things I would do if I had time, space and money. 

 

I think my ideal design would be: Start at the plane where my harness bar currently is, make a hoop that goes to the top and welds to the roof. Have the sides so it bolts to the factory holes or just go all out and gusset to the side, goes through the wheel well and welds to an out rigger that welds to the frame rail connector. The legs go back and hits the shock tower, then continues back and hits the floor with a cross brace, continues through the floor and comes out through the rear panel where it has a plate so I can do a sacrificial rear bumper/bash bar that has an integrated jacking point tucked under the car that meets up with the bars that went through the floor.

 

Speaking of I forgot I have an inner brace for the rear subframe where my fuel cell mounts, basically a 1x1 box structure that bolts to welded brackets on the sub frame to hold my fuel cell. I guess my rear is even more together than I thought.

[Neverdone]

Got any pictures of what you have now? 

[JMortensen]

I've got some thoughts about that roll bar design:
1. Don't like the X up high. Too much weight, and you're reinforcing the strut towers with the top of the tube where it isn't very stiff. 

2. I would do the backstays to the top of the strut tower. Plate that whole trapezoidal area and weld the stays to the plate.

3. The bars in yellow are great if you are connecting to door bars on the other side of the main hoop. Without door bars I think it's just extra weight to carry around.

4. If you want an X, you can do it low, from the strut towers to the bottom of the hoop. I did this on mine. Would be MUCH easier to install if you cut out the storage cubbies. I didn't. 
5. I'd just go with a straight bar across the strut towers

EDIT--Also connect the top of the hoop to the map light area of the roof with a shear plate.

Edited March 29, 2018 by JMortensen

[Nelsonian]

Here's how my 4 pt roll bar was constructed.

Edited March 30, 2018 by Nelsonian

[primaz]

for a street car these few pics should give you an idea of what I have on my two street cars and I feel that this is ideal for chases stiffness without the wasted space and issues bars for a street car.  I can jack the car up with a jack stand and have three wheels off the ground; it give me the stiffness of my crazy Primadonna Z car with a 9 point cage so for street use I think this is ideal.  If you worry about rolling the car you can add a basic hoop but no need to do the rest of the roll bar work for street as that just becomes a pain for anyone else you give a ride to, as they will not like the bars interfering with easy entry in the car, etc.  Believe me very few women want to ride in a car that is too caged.  This boxing of the frame rails goes from the front all the way to the rear sub frame and is boxed inside as well.  It follows the factory fake rails and give is true strength of a framed car or a Z with a cage without the bars in the way for a street car.  Unless you really want to compete for a track I think this is way better.

[260DET]

Link to AU regs which show variations of designs using self explanatory sketches, a handy design reference  http://docs.cams.com.au/Manual/GeneralRequirements/2018 Edition/GQ11-Schedule J-2018-1.pdf  As Jon has mentioned this is the time to consider structural aims, from my observations this is often neglected. The priority, tag the cage to the body wherever possible which requires the builder to keep the bars close to the body which some of them don't like because it makes their job harder. In particular keep the A pillar bar snug, the common idea of having a big plate with lots of 'structural' flanged holes spaced away from the pillar gets me, other than looking fancy it's nonsense from a driver visibility and a structural point of view.

 

[EF Ian]

On 30/03/2018 at 1:53 AM, JMortensen said:

I've got some thoughts about that roll bar design:
1. Don't like the X up high. Too much weight, and you're reinforcing the strut towers with the top of the tube where it isn't very stiff. 

2. I would do the backstays to the top of the strut tower. Plate that whole trapezoidal area and weld the stays to the plate.

3. The bars in yellow are great if you are connecting to door bars on the other side of the main hoop. Without door bars I think it's just extra weight to carry around.

4. If you want an X, you can do it low, from the strut towers to the bottom of the hoop. I did this on mine. Would be MUCH easier to install if you cut out the storage cubbies. I didn't. 
5. I'd just go with a straight bar across the strut towers

EDIT--Also connect the top of the hoop to the map light area of the roof with a shear plate.

Thanks for your thoughts.

 

I can say now that whatever cage goes into my car won't be perfect, it will be a compromise because I'm trying to have a car that car is good at many things, its mainly a street car and I want to  keep that classic feel to it and don't want to loose interior functionality. It also has to be capable on a circuit and on a drag strip.

 

 

1 - X up high - good point, I can do without an x and just use 1 diagonal bar to save weight. 

 

2 - I would like to do the backstays to the top of the tower, but doing so would mean loosing my seatbelts and I sure as heck don't want to be running harness anywhere other than on track. If you have any idea as to how I can re-engineer my seatbelts to somewhere else them let me know.

 

3 - Will do without these bars

 

4 - Again, I want to keep the interior nice looking and as original as possible so I don't really want to have bars running there.

 

5 - Not sure what you mean, the bar is straight across the towers, albeit slightly forward of where would be ideal, if this is what you mean I could always have it right across the middle and have this bar separate from the rest of the cage.

 

I will be connecting with a plate to map light area.

 

 

 

 

This is about as good a cage I get while keeping the seatbelts and keeping weight down, will it still have enough of an impact on stiffness to be worthwhile?

 

[rturbo 930]

For the reasons I stated earlier, you're going to have to re-engineer your seat belts regardless since your main hoop is going where the lower seat belt pockets are, and I don't see how they can both possibly occupy the same space. My plan was to do what you show in the picture above there - mount the bars to the front of the strut tower where the strut bolts in - unless there's something I don't know, I can't imagine that would be much worse than having it on the top of the tower.

 

Interested to see what you do, since I'm facing the same problems.

Edited April 1, 2018 by rturbo 930

[EF Ian]

I'm not sure, might be able work with it:

 

 

 

 

What doesn't help is that I work away from home, so I can't actually physically check things, doing all my planning from my memory and photos.

[rturbo 930]

No seat belt reel? Doesn't look like it even has a pocket for it. My '76 has dual reels, and so does my '78. Interesting. If I could get my hands on whatever belts the late euro cars had, that would make my life a lot easier.

[EF Ian]

 

 

 

 

 

 

 

 

[280Z-LS3]

If your serious about a full cage go old school, vintage BSR-260Z-IMSA design.  Since my 280Z will be street driven like the OP's car I will most likely build something similar to Dan's Street Cage design.

 

Love these old photos.

 

 

 

 

Edited June 21, 2018 by jsulse

[JMortensen]

Looking at your cad drawing I have a couple suggestions. First is the strut tower to dash bar. Hitting the middle of the dash bar is not ideal because there is no load path. The BSR car had the tube from the middle of the dash to the main hoop. Also not the best, but a lot better than just ending in the middle of the dash bar. Built the way you drew it, it will probably be an improvement over no strut reinforcements, or reinforcements to the (weak) firewall, but a better idea is to do an X from the strut tower to the dash hoop, and then hit the dash hoop on the other side with the upper door bars. I don't know how much interior you're going to have but it's tight in that area. Also will probably have to have a plate on the inside of the firewall and then bolt in the part in the engine compartment so that you can take the engine out. I actually have the bars as you have them and I had to tweak the windshield wiper linkage to clear where they went through the cowl.

Another issue is the shoulder bar is bent back for seat clearance (necessary if you're over about 5'7" or so. The problem is that your diagonal looks as thought it is bent back to the bent shoulder bar. That's illegal per SCCA, NASA, etc. You could put the diagonal in the main hoop and then put a short tube in to connect the diagonal to the shoulder bar, or you could do a straight bar across the pass side and then bend around the back of the driver's seat.

I was also able to take bars from the bottom of the A pillar to the strut tower. It managed to squeak in without interfering with the clutch pedal. Not hard to do and the stronger the strut tower reinforcements are, the better.

 

[jpndave]

I'm late to the party on this thread. Here's a quick suggestion on your latest drawing. I'll read the whole tread and give a more in depth reply later. Nice car BTW EF Ian you have some pretty details in there.

 

Pardon the crude tablet finger drawing. Yellow delete/move to blue. Green and additional (not shown) diagonals on the main hoop ideal but probably a no-go because of the seats. Lower diagonal blue will help a lot instead. Join all the tubes at the circles as high as you can -same point all tubes. Only one triangle per opening is needed, 2nd the input that "x" braces generally just add weight don't add much strength. I'm going to tie the lower front subframe all the way back into where the main hoop is attached at the floor and spread the box out to catch the hoop tie in if that makes sense.

 

The idea is to try and have all the tubes in tension/compression and every plane braced for sheer (triangles are your friend). All junctions should be at the ends not out in the middle of a tube unless you tie it in with another tube.