Roll cage building tips

Building crash structures for a race car is tough work. We brought you some advice on how to do it right.

http://grassrootsmotorsports.com/articles/roll-cages/

I don't mean to pick nits here... an article on "how to do it right" might contain such information as how tight the fit on a fishmouth needs to be to close the gap in one pass or options on how to get the main hoop tight to the ceiling and still be able to 360 weld it... or even how to calculate where a bend might terminate based on starting point and the radius so you can bend your own tubes. I see no "How to" information here.

That is "A Beginner's Primer: Buying a roll cage".

Another nit: the article touches on this by mentioning floor pans as being less than ideal, but the load path is very important. The best cage in the world doesn't do much good if it's mounted on an easily deformed structure. Some information on how to identify these structures and what to do if you can't get the cage on a sturdy part of the car would be good.

Related note: I failed a car at tech at yesterday's autocross for having a harness out of date (1995) and a roll "cage" that consisted of a generic weld-in rear bar with homemade, crimp-bent downbars and front halo made out of about 1.5" tubing with an s-bend. The owner managed to HAND HACKSAW the added-on tubes out of the car and come back to tech in under 10 minutes!!!

Giant Purple Snorklewacker wrote: I don't mean to pick nits here... an article on "how to do it right" might contain such information as how tight the fit on a fishmouth needs to be to close the gap in one pass or options on how to get the main hoop tight to the ceiling and still be able to 360 weld it... or even how to calculate where a bend might terminate based on starting point and the radius so you can bend your own tubes. I see no "How to" information here. That is "A Beginner's Primer: Buying a roll cage".

Yeah I saw that and thought maybe I will be but able to use some tips from that to build a roll bar for the Yugo but it didn't tell me anything that would help over what I already knew.

Javelin wrote: Related note: I failed a car at tech at yesterday's autocross for having a harness out of date (1995) and a roll "cage" that consisted of a generic weld-in rear bar with homemade, crimp-bent downbars and front halo made out of about 1.5" tubing with an s-bend. The owner managed to HAND HACKSAW the added-on tubes out of the car and come back to tech in under 10 minutes!!!

Interesting, every autocross I've ever been to didn't require roll cages. And if the roll cage is at least well-attached to the car, I don't see how it could fail tech at the auto-x.

I've done tech at LeMons races and at auto-x, and auto-x tech is MUCH more lax. I've seen guys apparently put a lot of trouble into a "cage" for their auto-x car and I just chuckle inside when I see it, knowing it's pretty much useless and I'd flunk it immediately in the LeMons context. But for auto-x, sure, knock your socks off.

Similarly with the harness, I've never seen a harness required at an auto-x. Heck, I've seen them where all you need is a lap belt.

Last I saw belt dates didn't apply at the AX level or HPDE (at least in SCCA). Once you move to Time Trial now the dates apply, for instance this is the last year I can use my harness in hillclimb but it's OK for AX. Of course, if the belts are cut/slashed/frayed to the point of not being safe, yeah it's fail time.

I'd have to go back and look, but IIRC A Mod, B Mod and F440/500/SAE are the only AX classes which require a roll structure and even it is not all that stringent.

He does porsche club or nasa or something. Dont think it's scca.

In reply to volvoclearinghouse:

Neither a cage or belts are required for us, but our insurance mandates that if a car has them, then they have to be up to spec. The "cage" was scary though. I honestly think that if the guy had touched a wall (we've had one in 5 years) it would folded like an accordion and killed the guy. It really was that bad.

But, he cut out the added-in crap, ground down the stubs, put the leftover foam (hot water heater insulation) over the spots, and swapped the stock seatbelt from the passenger side.

I also failed 15 people for Snell 2000 helmets. 12 of them claimed the SCCA allows them. If true, the local region is violating national SCCA policy...

SA2000 is still AX legal, the 1995 standard is no longer legal. Pics of SCCA legal helmet decals:

http://scca.cdn.racersites.com/prod/assets/2012_Solo_helmet_cert_decals.pdf

SA2000 is no longer TT legal.

Curmudgeon wrote: SA2000 is still AX legal, the 1995 standard is no longer legal. Pics of SCCA legal helmet decals: http://scca.cdn.racersites.com/prod/assets/2012_Solo_helmet_cert_decals.pdf SA2000 is no longer TT legal.

Good to know, thanks. Too bad for those guys that our insurance mandates Snell 2005 or newer, just like HPDE, TT, and Club Racing.

FYI - the national Corvette club requires non-expired harnesses for autox. But if you have stock belts, they're okay. Even if they're in an X1/9.

I once saw a CRX get through autocross tech with a harness where the shoulder straps were duct-taped to the back of the seat.

Javelin wrote:

Curmudgeon wrote: SA2000 is still AX legal, the 1995 standard is no longer legal. Pics of SCCA legal helmet decals: http://scca.cdn.racersites.com/prod/assets/2012_Solo_helmet_cert_decals.pdf SA2000 is no longer TT legal.

Good to know, thanks. Too bad for those guys that our insurance mandates Snell 2005 or newer, just like HPDE, TT, and Club Racing.

Having club saftey rule very different than SCCA's is not all that uncommon. Too bad, certainly, but gotta meet your rules, not SCCA's if you are not them.

I heard that SCCA does not require roll bars for open track days- our club does. And almost required them for closed cars that had certain number of modifications (roughly a very underpreped SP car).

Keith wrote: FYI - the national Corvette club requires non-expired harnesses for autox. But if you have stock belts, they're okay. Even if they're in an X1/9. I once saw a CRX get through autocross tech with a harness where the shoulder straps were duct-taped to the back of the seat.

They also used to requre that non-vettes carry a fire extingusher. Even though if a fire started, it would be worse in the glass cars...

We helped them lobby to change that rule.

(Local NCCC rocks around here)

I should clarify that the duct-taped CRX did NOT get through NCCC tech, but a local race promoter who had never actually seen an autox before.

I've never seen tech at an autocross. I'm OK with that.

Giant Purple Snorklewacker wrote: I don't mean to pick nits here... an article on "how to do it right" might contain such information as how tight the fit on a fishmouth needs to be to close the gap in one pass or options on how to get the main hoop tight to the ceiling and still be able to 360 weld it... or even how to calculate where a bend might terminate based on starting point and the radius so you can bend your own tubes. I see no "How to" information here. That is "A Beginner's Primer: Buying a roll cage".

Thanks for the heads up. I saw that OP, and was pretty pleased since this is relevant to my interests. (e.g. see my recent roll bar threads.) Will somebody please threadjack this conversation and offer the answers that the article doesn't have? You can start by answering GPS's examples.

1) How close does a fishmouth need to be to close the gap in one pass?

2) How do you get the main hoop tight to the ceiling and still weld it all the way around (not relevant to me since my roll bar is going in a phaeton, but I'd still like to know.)

3) What are the calculations needed to make your own bends?

BTW, this is another example what SkinnyG and I were saying in the reader survey thread; a lot of GRMers would like to see more articles on how to do things and less on how to install something you purchase off the shelf.

JoeyM wrote: BTW, this is another example what SkinnyG and I were saying in the reader survey thread; a lot of GRMers would like to see more articles on how to do things and less on how to install something you purchase off the shelf.

This. I could only +1 and assure you that I gave the same response to the survey. More tech. And TECHY tech, not how to choose a paint shop, but how to prep and paint in your garage. Not how to pick a welder, but how to apply welds in a car specific environment (does it really dick up the alternator/cpu/seat vibrator to weld on a car?), how to build a safe roll cage, etc.. I just thought I was being picky. Sometimes you look at Hot Rod or some other mag like that where they get really deep into tech, and that is really what I want, but applied to sports cars. GRM may not have that direction though.

I think they need to move in that direction.

Teh E36 M3 wrote:

JoeyM wrote: BTW, this is another example what SkinnyG and I were saying in the reader survey thread; a lot of GRMers would like to see more articles on how to do things and less on how to install something you purchase off the shelf.

This. I could only +1 and assure you that I gave the same response to the survey. More tech. And TECHY tech, not how to choose a paint shop, but how to prep and paint in your garage. Not how to pick a welder, but how to apply welds in a car specific environment (does it really dick up the alternator/cpu/seat vibrator to weld on a car?), how to build a safe roll cage, etc.. I just thought I was being picky. Sometimes you look at Hot Rod or some other mag like that where they get really deep into tech, and that is really what I want, but applied to sports cars. GRM may not have that direction though.

+2!!

I gave the same response - citing Angry's brake article as the gold standard and now that I think about it - that was possibly last time something of that completeness appeared.

JoeyM wrote: 1) How close does a fishmouth need to be to close the gap in one pass?

What I have seen with all the drag cages I see, is that 1/16 to 1/8 depending on material and welding method. And if you need more then one pass, give up the welder and tape measure and leave it to the professionals.

JoeyM wrote: 2) How do you get the main hoop tight to the ceiling and still weld it all the way around (not relevant to me since my roll bar is going in a phaeton, but I'd still like to know.)

Depends on the car. you can hack off the roof off a SN95 Mustang and get within .5" of the headliner. The exterior pillar covers hide the sins of chopping the roof off. My CM bar in my old 89GT was about 1.5-2" lower then the headliner. But if you read some of the rulebooks, as long as you add a 360 degree welded in gusset, you don't have to weld all the way around the tube....

JoeyM wrote: 3) What are the calculations needed to make your own bends?

Get the cheap bend programs out there or you can bend up TIG welding rod to your liking and measure all those out.....

JoeyM wrote: BTW, this is another example what SkinnyG and I were saying in the reader survey thread; a lot of GRMers would like to see more articles on how to do things and less on how to install something you purchase off the shelf.

Agreed. Don't feel we need to reinvent the wheel, but buying everything out of the catalogs gets old.....

If I can get by the garage tomorrow I'll post the relevant maths for bend radius and length. it's actually very easy math.
I have all my notes there, sadly.

JoeyM wrote: Thanks for the heads up. I saw that OP, and was pretty pleased since this is relevant to my interests. (e.g. see my recent roll bar threads.) Will somebody please threadjack this conversation and offer the answers that the article doesn't have? You can start by answering GPS's examples. 1) How close does a fishmouth need to be to close the gap in one pass?

I'll take a stab...

I like to keep them 1/8 or less but I have messed up and gone a whole quarter inch with .030 wire on a non-required tube. That is not a definitive answer - I am just a hack who made his own cage out of metal and brawn and tight fit all the way up to about 1/8 was really easy to drop a nice consistent bead on. When it got a little wider things got messy and I didn't like it. BTW, making everything a tight fit is time consuming and often frustrating. Metal is an unforgiving motherberkeleyer that cannot be reasoned with. It requires much patience. Like kung fu or rubbing your woman's back in the hopes you will get a little.

2) How do you get the main hoop tight to the ceiling and still weld it all the way around (not relevant to me since my roll bar is going in a phaeton, but I'd still like to know.)

Either you tack it, cut holes in the floor and allow it to drop down, then insert plates after you weld it or you shorten the legs and make plinth boxes to set it on top of. It depends on the chassis, how much weight you are willing to add to the build and how much real metal you have to work with in that area. See above disclaimer again. I ask a lot of questions, copy from pros and then make my own way... no guarantee there is not better magic to be learned from say... a well written technical article that a professional might share :)

3) What are the calculations needed to make your own bends?

Rather than me re-type or paste, you read this until you find tube bending method #1: http://www.jd2.com/download/M3B%20Directions.pdf

Then adjust accordingly for tube diameter and radius of the die. After you do a bunch it becomes pretty routine and you get a feel for it. Then you can ad-lib a little and expect things to turn out alright. For the first cage - buy extra tubing.

Wasn't there a much techier roll cage article in the series for the SAAB build a few years ago?

Alan, maybe when the SAAB cage build surfaces from the archives it could be linked at the end of the Bar Hopping piece?

Or just tack all your tubes into place and fully weld outside the car like this: