Help with roll cage

[crackler]

WOW, what a thread. . .

I called a local race shop for a roll bar, down bars and a harness bar. They said it would be about 500.00 for the whole set-up. If you don't need a cage, and are just looking for roll protection I would consider a proper roll bar as an inexpensive alternitive. All real cages are welded together PERIOD.

Also, a cage in a street car is a BAD idea, I have a hard head, but steal is harder.

Find a local race shop, A real one, not some import tuner shop. A place that biulds cages for a living, look for some one that can build NASA, SCCA, or the like spec cages that will pass a tech inspection. Tell them what your goals, and needs are and ask them what they suggest, and how much it will cost. I bet it will be cheaper than you might think. Best way to find a good shop is to get a hold of some real racers, go to the local track, or find a locul forum or something in your area, and ask who does good work. I know several people in KC that build cages, FWIW.

Also, my roll bar in my miata, which passes SCCA crash testing is all welded together. It bolts into the chassis in four places with huge backing plates and bolts to the seatbelt tower in four places.

.02

FLAME AWAY!

[AmoebAssassin]

Have you tried to comprehend any of my posts before you reply? I never said I didn’t trust the safety of those cars. I said I am not concerned with those types of racing because I don’t compete in them. I explained why I ran a bolt in cage, I wanted to keep full Interior. I could have fabricated my own weld in cage for cheaper then the price I paid for my safety 21. The cost was not the issue. I have a daily driver, I wanted a cage in this vehicle for the fact of I will not run bucket seats and harnesses with out one. I even welded a harnesses bar into my cage.

You opted for a more expensive option, even though that option is generally only allowed in D1, and few other standard motorsports...that seems illogical to me.

Regardless -- for the record, one of the local 240sx guys has a chassis with a NHRA 8.50s legal full weld-in cage, WITH the full interior required for his class, so weld-in with full interior is definitely do-able, and I've seen it with my own eyes. I'll try to find you some pics.

Quote »Ok so now I understand you want the tensile strength of the weld, and the shear strength of the bolt.

The tensile strength of an average weld is 70,000 psi The shear strength of a fine-threaded hex bolt has a minimum shear strength of 95,000 psi

If you scroll back up ^ to the picture of that STI cage, one can see that the tabs are welded all the way around the main hoop. So two tabs holding the joint together are twice the length.[/quote]I agree that a bolt in shear is typically stronger than a weld in tension, however, the real safety gain going from a bolt-in cage to a weld-in cage is the elimination of the tabs inherent in the design of a bolt-in cage. Even though the tabs are welded all the way around the bar, tabs are only strong when they are loaded purely in tension and compression. However, when a car rolls, the impact mechanics will almost never exert a purely planar load on the tabs. There will always be large amounts of bending and torsion in the tab when a car experiences a collision with a bolt-in cage. Because of the large out-of-plane loads on the tabs, they are VERY prone to bending, and are likely to fail as the act of impact/rollover continues. I've actually seen this effect first-hand on a local kid's civic w/ bolt-in cage.

Quote »How do you weld fiberglass together? Take the Corvette, its a production car.[/quote]Corvettes have always been metal frame cars and no production version has ever featured a composite monocoque. The extensive use of composites is mostly in the exterior body panels (as well as the floor pan of the C6 Z06). These body and chassis panels are bolted to the metal structure, which absorbs and distributes more or less the entire load of cornering and collision.

As for your comment that the OP doesn't need the benefits of a weld-in roll cage -- I think it's prudent, as far as roll cages go, to get the safest option -- you never know when you're going to need the protection. Why short change yourself and end up regretting it later if you are, god forbid, involved in a serious accident?

[koukicody]

damn, havent seen Neel post in forever! I've missed your uber-pwning's lol

[Joe]

damn what the hell did i miss?

1) cusco cages may be 100% legal in japan but in the US they are not legal for use by ANY sanctioning body. PERIOD. and last i checked most of us posting in this thread are from the US. D1 isnt running here anymore (in fact, they are about to tank in japan too if anyone cares, thats right D1 is about to disappear). SEVERAL of their cars/drivers are coming over here to run FD in 08 and are having to totally redo cages and get new helmets because japan's safety requirements are so relaxed. here a cusco cage is a show cage. nothing more. go have your autopower or kirk racing rollbar powdercoated or anodized blue and it will be the same damn thing just 10x safer.

2) there is nothing wrong with a bolt in cage. the shear strength of 1 grade 8 bolt in that size is like 150,000psi. and theres 3-4 per plate, and 4 plates. if you are breaking a bolt in an accident, you are GOING TO DIE NO MATTER WHAT KIND OF CAGE IS IN YOUR CAR hahaha

3) roll cages dont belong in street cars. rollBAR'S are fine so long as you have adequate head clearance between the main hoop and your noggin.

now lets take a look at this picture, which scares the jesus out of me



THAT IS NOT SAFE. i dont give a **** who you are, that is NOT SAFE AT ALL. the diagonal brace should NEVER meet another support bar in the middle (weakest point when you supply stress). if that car rolls over you are now basically inside of a jungle gym instead of inside a cabin. the main hoop is multiple bolted together pieces. it doesnt look like they are even behind the drivers HEAD let alone behind the SEAT where they belong. you basically have a 1.5" diameter metal tube next to your head now when you wreck (the same reason why a cage doesnt belong in a street car) and the rear support tubes are bent, what the **** are they going to support if the car rolls? whoever calls that a roll cage should be shot. thats a death trap.

THIS is how a rollbar/back half of a cage should look

the main hoop is 1 piece, not bolted together, the diagonal brace would actually *do* something to prevent the roof from caving in, the support braces also *gasp* support the main hoop if the car rolls!

no bends anywhere on any core support structure other than whats necessary.

if someone brought me a car with a cage that looked like the cusco one, i would laugh them out of my event

cusco cages dont belong anywhere near a car that gets driven.

[crackler]

Wow I just noticed this. Look at NismoFly's new screen name.

Quote, originally posted by nismofa g » Let me know when a cusco cage lets joey hand walk away from cartwheeling 8 some odd times in his m3 at mid ohio, because ill probably be to busy watching pigs fly...

Oh, and Amen Kamin!

[1fastredsc]

While SAE grade bolts are higher in tensile ultimate strength than most rod filler (you can actually get steel filler with a higher strength than 70ksi, 7018 isn't the only rod out there), the bolts themselves play a different game than welds. Weld surface area depends solely on the welder and number of passes made to fill a void. It wouldn't be hard to weld around the plates of a weld in cage and get close to the surface area of the bolts you would have used. Second welds, with the exception of slight cooling distortion, don't have any residual stress, they only take a load when stressed. Bolts on the other hand always have a constant clamping force plus any other loads, and if you shear them with the clamping load they already have than we are talking Moore's circle analysis and out of plane stress failure. Lastly, threads on bolts are stress concentrators plane and simple, meaning that normal stresses at the plain shaft of a bolt can becoming 50% to twice as large at the threads. In the end if it's approved for the motorsport that you are competing in, than it means that someone did the analysis to certify it meets or exceeds the demands. If it's approved, than use it. But don't try to speak engineer if you aren't one

[1fastredsc]

One more thing to add. You also have to consider mode of failure for a material. Those high strength steel bolts are much more brittle in failure than the mild generic steel used in roll cages. Therefore during impact if a brittle material yields it will just fracture and break but a ductile material will actually distort during yield and absorb a lot of impact energy possibly saving your life.

[bmadd2402]

IIRC, the cusco isnt even a roll cage, it is a "Tension cage!" my advice to the guy: get some experiance, then decide under which sanctioning body you want to race, get their rule book, or rulebooks if multiple series, and take them to a fabricator. The requirements are pretty cut and dry. Autopower is approved for scca, and you can always add more to the cage if need be. Start with a 4 point, the move forward as need be. a decent custom 4 point only costs a couple hundred bucks here in dirt track country.