Cage thread

[turtl631]

Now that finals have rolled around, it has become important for me to become very interested in some aspect of car building so that I have a valid reason to avoid studying. I'm kicking myself a bit at this point for the current setup in my car (Kirk 4 point rollbar, g-force camlock 5 point belts, spl driver seat, memoryfab humongous passenger seat) since I've done 1 track day since it was all installed. So, streetcar express for me, although i don't drive much so it doesn't particularly matter either way. Plus, I got a good deal on most of the stuff.

Moving on from my regrets, I was thinking about where I want to go with my car in a few years once I graduate/move and I hope to get something cheap as a DD so I can really go further with the S14. Not track only, but more of something that you can just barely drive to the track, and have fun with on weekends on a nice day...toss the carpet and rear interior, add lightness, maybe something along the lines of an NT-01 if I can drive the car enough to get to that point.

Bolt in roll bars are pretty lame, so it will definitely be sold and I'll get one welded in. I've seen some pretty questionable elements in most pics of 240 cages I could find though, so I thought we could start up a thread with pics and commentary. Def, I know you got a rollbar welded in and I haven't seen pics. Wissass, you have good pics of work you've done on your site so I'll probably ask about some of those too. Andy's cage looks good, if a bit on the heiffer side of the safety/weight continum. I guess if you can't buy an S14 you can at least make your S13 weigh as much as one.

I'm actually really curious what logic people use when building cages, and when I have a chance I'll post up some pics of specific cages and ask about elements that struck me as odd.

[sr20goofus]

I have a weld-in roll bar almost identical to Andy's, where he got his idea.

My rollbar will eventually be turned into a cage so all th extra bracing thats difficult to get to in a coupe was done first to avoid the later hassle. Safety is #1 priority when building a cage, dont skimp or make sacrifices. I am getting my cage done end of winter i am hoping, with NASCAR drivers door bars, and everything else basic, but fitted for my large self. Slightly larger tubing was used because the shop i went to only had one die for the bender, so i went with thicker rather then thin walled tubing for safety. Who knows i may never need my cage to actually serve as a function in the future, but the one time i really need it, i want it to work flawlessly.

My cage design follows the NASA CCR rules and reg's to make sure when i go through tech the day go to Comp school in 2010 i pass without a single question. Certain things are overkill and arnt necessary if the cage is done correctly. I am not a fan of gussets everywhere, not my style since they are for chassis stiffness and not safety. Making a car super light and having a nice 6pnt cage arnt that easy with S13's because youd have to buy all FRP/carbon front body panels to make up for it. My race weight with me in the car will most likely be around 2750 after the cage is done. If i want to make it lighter im sure i can get down to 2600 without buying expensive panels, but ill have to sacrifice some things i have now.

all my $0.02, im in it for safety above all else.

[veilside180sx]

Andy's is the best basic design you'll find. It supports where it needs to, and doesn't where it's not necessary. It's easy to add the front portion when needed as well.

[2Fass240us]

Andy's cage looks good, if a bit on the heiffer side of the safety/weight continum. I guess if you can't buy an S14 you can at least make your S13 weigh as much as one.

Ha, ass.

I am not a fan of gussets everywhere, not my style since they are for chassis stiffness and not safety.

Added strength from gussets can aid stiffness AND safety.

[Wiisass]

Let me know if you have any questions about design or anything I've done on any of my cages.

Pics are all here:

http://www.tipengr.com/gallery/cages/

I don't think I've done any of them the same, each one is a little different, a little better or I try a new method or change something up to make it fit better, be easier to do, etc.

Right now I'm working on the supra and pretty excited about it. I'm trying some new things out on the car because it's finally one of my cars that I'm working on. So I have a little more freedom and time that I can dedicate to it and no risk of the customer not liking how it came out.

And by the way, gussets are so much cooler than safety.

[sr20goofus]

Ha, ass.

Added strength from gussets can aid stiffness AND safety.

see andy, i believe the cage should be made tight against the chassis where gussets arnt needed, remove all possible crush zones and the car is safe, alot of times people use gussets to fill in large gaps where the cage is loose. The guys down at Piper Motorsports showd be cars that had rolled over in SCCA races and such that were hardly damaged because the cage was so tight to the chassis.

[veilside180sx]

see andy, i believe the cage should be made tight against the chassis where gussets arnt needed, remove all possible crush zones and the car is safe, alot of times people use gussets to fill in large gaps where the cage is loose. The guys down at Piper Motorsports showd be cars that had rolled over in SCCA races and such that were hardly damaged because the cage was so tight to the chassis.

Even with the cage close, the gussets are still necessary, imo.

A cage is meant to provide safety, and chassis stiffness. The less flex in the chassis, the more consistant the suspension can function w/o the chassis acting as part of it.

[turtl631]

Let me know if you have any questions about design or anything I've done on any of my cages.

Pics are all here:

http://www.tipengr.com/gallery/cages/

I don't think I've done any of them the same, each one is a little different, a little better or I try a new method or change something up to make it fit better, be easier to do, etc.

Right now I'm working on the supra and pretty excited about it. I'm trying some new things out on the car because it's finally one of my cars that I'm working on. So I have a little more freedom and time that I can dedicate to it and no risk of the customer not liking how it came out.

And by the way, gussets are so much cooler than safety.

http://www.tipengr.com/gallery/cages/rich_s14/DSC01104.jpg.html

For this S14 cage, why is there just one diagonal brace for the main hoop? The off the shelf rollbars are usually like this too and I've always wondered what the reasoning was. Also, is there any utility in adding a bar between the bottom of the main hoop and the rear shock tower? Asking that makes me wonder what are the main areas where flex occurs in a stock 240SX?

http://i116.photobucket.com/albums/o...0/Cage/002.jpg (Andy's cage)
I like having the X brace for the rear towers go to the bottom of the main hoops, drops the CG a bit. Again though, why are there non paired diagonal braces? I'm not seeing the logic of designing asymmetry into a cage. Another nice thing on his cage is the horizontal bar just above the driveshaft hump, which I haven't noticed on any other S chassis cages at this point.

[Wiisass]

How many cages are you seeing that have two diagonals in the main hoop? I've never put more than one and don't plan on putting two in anything. It could make it a little stronger, but so could adding bars everywhere, but I don't think it's really worth it. I mean who really cares about the passenger?

Is there a reason for wanting a second diagonal or is just the triangulate everything rule that people always say? I mean with one diagonal and if you were to rollover and have it hit right above the passenger's head, it would still take a lot of force to bend the cage. Look at the load path through the cage and how it is constrained.

I don't really think that the lower X's are necessary. They don't really drop the CG much, if at all and they're additional weight, so that's not a very good reason. But you have to think why you would need bars down there. Is the beaming stiffness of the stock chassis that low? They don't seem to provide any direct safety help. I'm not saying they don't help, it is nice to connect everything, but I'm just not sure they're really worth it on a car like these. If you tie the rear down bars and base of the main hoop to the chassis correctly, you shouldn't need any additional bars connecting those points because they are already tied together by the chassis. It's kind of like welding in a rear bar between the shock towers and the bolting on a rear shock tower bar.

And asymmetry isn't necessarily a bad thing. You need to look at the whole design. Where the loads go both from the suspension and in the event of a crash. Doubling up on triangulation can add more weight than it does stiffness and then it wouldn't be worth it.

[Epstein]

I've got some stock convertible pics and other info to add to your caged pics... What do you think of the stock/OEM vert reinforcements as far as chassis stiffening? They basically boxed the floor pan and put a beam through the middle, plus reinforced the firewall/strut tower area. It's pretty heavy material, too. Say someone just wants to increase chassis stiffness in a backyard, Opera kind of way without a cage. Good choice to persue this?

[Def]

I'll try to get pics of my rollbar up, but it's relatively simple since there is just no point in going ass crazy if you don't go all the way forward and cage it. It'd need to go through the firewall to the strut towers, have extra vertical door bars and gussets up around the A-pillar area etc.

Yea you can triangulate until you're blue in the face, but you're not going to easily twist the chassis in the rear with just a simple rollbar and a few gussets(which I still need to add to mine), and like Tim said, at some point the added increase in torsion/bending/whatever is an almost immeasurably small amount for each added bar, and you're probably adding 5-10 lbs for each bar span so you've got to weight the pros and cons.


As for cage/rollbar fitting, I think each outside point should be within 1-1.5" of the inside sheet metal. You can still gusset to add stiffness with a smaller dimple die, or mounting the gussets at a shallower angle and boxing the top and bottom of the gusset.

[Def]

I've got some stock convertible pics and other info to add to your caged pics... What do you think of the stock/OEM vert reinforcements as far as chassis stiffening? They basically boxed the floor pan and put a beam through the middle, plus reinforced the firewall/strut tower area. It's pretty heavy material, too. Say someone just wants to increase chassis stiffness in a backyard, Opera kind of way without a cage. Good choice to persue this?

It'd probably be easier to add strength and keep the weight down by making reinforcements yourself.

Then again, the most I'd do would be to further box in the middle of the framerails in the middle of the car. You could maybe make some plates to strengthen the a-pillar to roof location, but I have to wonder how strong the A-pillar and roof themselves are. Most of the flex might actually be in the members themselves.


I think a little bit of gusseting to the strut tower and some fender braces might get you most of the way towards stiffening up the car that you're really going to get without caging it.

[turtl631]

How many cages are you seeing that have two diagonals in the main hoop? I've never put more than one and don't plan on putting two in anything. It could make it a little stronger, but so could adding bars everywhere, but I don't think it's really worth it. I mean who really cares about the passenger?

I saw a few while searching forums/google for cage pics to see what's out there.

I don't really think that the lower X's are necessary. They don't really drop the CG much, if at all and they're additional weight, so that's not a very good reason. But you have to think why you would need bars down there. Is the beaming stiffness of the stock chassis that low? They don't seem to provide any direct safety help. I'm not saying they don't help, it is nice to connect everything, but I'm just not sure they're really worth it on a car like these. If you tie the rear down bars and base of the main hoop to the chassis correctly, you shouldn't need any additional bars connecting those points because they are already tied together by the chassis. It's kind of like welding in a rear bar between the shock towers and the bolting on a rear shock tower bar.

Actually what I meant was that I liked how the rear X went down rather than up, but his cage also has one diagonal bar that goes to the top corner of the hoop. It makes more sense to me to have two bars going from the top corners of the hoop to the shock towers and then the X going to the bottom corners of the main hoop than to have the X also go to the top corners (a la your S14 cage I posted pics of). I get your analogy to the rear bar/shock tower bar though, and looking at the pic of Andy's cage again, there's a stock brace parallel to that lower horizontal one and about a foot away from it, so that may be a bit redundant.

And asymmetry isn't necessarily a bad thing. You need to look at the whole design. Where the loads go both from the suspension and in the event of a crash. Doubling up on triangulation can add more weight than it does stiffness and then it wouldn't be worth it.

Word. That's part of the reason I started this thread, to sift through the ideas out there and figure out which elements are actually important. Or we could just all build Koguchi style teepee cages. Ahmed, you showed us that pic a while back, so you can be first.

[Epstein]

It'd probably be easier to add strength and keep the weight down by making reinforcements yourself.

Then again, the most I'd do would be to further box in the middle of the framerails in the middle of the car. You could maybe make some plates to strengthen the a-pillar to roof location, but I have to wonder how strong the A-pillar and roof themselves are. Most of the flex might actually be in the members themselves.


I think a little bit of gusseting to the strut tower and some fender braces might get you most of the way towards stiffening up the car that you're really going to get without caging it.

I like a lot of the pieces individually, and it's because they mimic bolt-on parts that came years later. The front reinforcements = fender braces. Front lateral floor member = tunnel brace. Rear lateral floor member = rear cross brace. Rocker pieces = some bit from Doluck. Lateral pieces that tie frame to rocker = nothing on the market. All I need is a Dave Coleman ikea brace (trunk hole) and that rear ladder bar they put in the S15 Spec R's and that's everything known to man that's not a cage.

[nismofly]

I have to wonder how strong the ...roof

Roof is irrelevant, at least with cage, hence being able to get carbon fiber or fiberglass roof that is basically held on with glue.