hey everyone, I'm trying to figure out my plan for my roll cage/bar design.
my questions now have to do mainly w/ materials and a lil to do w/ design.

1. what tubing material and sizes are necessary? Chassis stiffening is my #1 concern, since the car is going to be just for street and autox, safety is not my main concern here. Also, i'd LIKE to keep weight to a minimum.

2. opinions on autopower's DOM bolt in 6pt, design looks good, DOM i hear is great, price is $800 range. any opinions?

3. I'm planning to attach the main hoop where the vertical wall from the floor to the backseat is, using the three surfaces (floor,vertical side panel, vertical rear seat panel), my cars' a four door civic, and im 6'2" tall so i sit back a lil.

4. I'm planning to run the front going bars along the top of the front-side windows and down the A pillar, my question now is should i run those bars straight down before the dash, into the frame rails just below the dash, OR should i run them along the A pillar into the huge colums of sandwiched metal at the far right and left sides of the firewall (firewall seems way stronger to me).

5. for the rear bars, where should they attach to the body? I was thinking, around the base of the shock towers, since the sandwiched frame rails run along that area (and its close to the upper control arms), or close to where the trailing arm pivot points (bushing) mount (back seat area). Ive noticed most Japanese tuners bolt in cages, they mount on the front facing side of the rear fender wells. Ive seen some ITA cars where they mount right where the shock tower bolts are. and lastly, the JTCC civics from 94/95 used 2 sets of criss-crossing bars, one set attaches near the shock tower, the others closer to trailing arm pivot point mounts, or possibly where the compensator arm bolts (except on the inside of teh body of course).

what do you guys think?
many thanks!
-steve

 

Most folks here will suggest that you not put a full rollcage in a street car. Something to do with all that hard steel in close proximity to your unhelmeted head. You might go with a 4-point rollbar, but be aware that you're giving up using your back seat either way.

That having been said, get the SCCA Solo rule book and see what their requirements for roll bars/cages are before you start planning. It'd be a shame to put in something that is illegal for the class you want to run.

For example, you say "I'm planning to attach the main hoop where the vertical wall from the floor to the backseat is, using the three surfaces (floor,vertical side panel, vertical rear seat panel)." SCCA Solo II rules state, in Appx C, A.2 "The top of the roll bar shall not be below the top of the driver's helmet when the driver is in normal driving position, and shall not be more than six inches behind the driver." So your main hoop might be too far back.

A good fabricator could probably answer most of your questions, or talk you out of something you don't really need. I have heard many folks talk well of Mitch Piper in Manassas.

 

but if you ran a race bucket and had a 5 point harness that was tied into your cage, wouldn't that negate the possibility of your head contacting the halo or a pillar of the roll cage?

 

No.

 

I may be in the minority on this point but, if the cage is padded as it should be, I have a difficult time seeing it as inherently more dangerous to the noggin than a typical, unpadded B-pillar... Particularly if there is an Expedition grill on the side of the tube opposite your skull - in which case the intrusion protection would seem to be worth the risk.

Kirk

 

No harnesses on the street please.

 

If you are going to run autox, you are limited to a reclinable seat(STS) a non-shell-type(STX) or a fully padded & upholstered seat(SP). This means that you can't use the safest race buckets. Also, 5-point racing harness is not DOT approved for street use(go figure). Besides, can you imagine a girl in a long dress trying to use a 5-point harness? Give up dating in that car.

I'd guess the problem with a roll cage is that the halo bars over the windows will be several inches closer to you than the normal sheet metal. And the sheet metal you can hit is already padded by the interior panels and has more give than a solid steel pipe anyway.


[Modified by Geezer, 10:19 PM 4/15/2002]

 

I run a 6 point cage in my E30 M3. I am seated very low and away from the bars, and there are no doorbars. I wear a 5 point exclusively, as the stock belt doesn't retract that well anymore.

Basically, my OMP fixed seat would have to come detached from the chassis, and my harnesses would have to fail.

Warren

 

Consider this the bare minimum you could/would ever put in a dedicated roadracing car. Adequate but far from best. For a street car, as mentioned, probably not the best option (with some exceptions).

PS- $800 range? No way, there are plenty of sources for these from $625 *shipped* (depending upon location of course... but you can still find 'em under $700 including shipping to the east coast...)

Jon

 

thanks for the help guys, but can you elaborate on why one shouldn't run 5 point harness on the street? realistically i drive this car maybe once a week, and i don't do autocross, so running a full race bucket is no big deal. keep in mind also that this cage i intend to put in is a fully custom chromoly weld in. also im a small person, so i can be situated in a position that is relatively distanced from the cage.

 

As stated above, they are not legal for street use in most areas. Also, running a harness without rollover protection is dangerous, since you can't get out of the way if the car *does* roll cuz the harness is holding you straight upright.
Not to mention they are a PITA, and using them for street use is inconvenient as hell. Also, people have a tendency to use them incorrectly and belt them too high, across the soft tissue of their stomach/torso, instead of down on your hip bones, where they are supposed to be. This is especially common in the 4 point harnesses, or if you leave the anti sub belt unbuckled, as one is likely to do in a commuting situation, cuz, well, they are a PITA.


[Modified by madhatter, 8:19 AM 4/16/2002]

 

No worse than a baby seat, and since I have the emotional maturity of one, I figure it's appropriate.

Not exactly a date car though "Yeah baby, just cut a hole through your dress for the crotch strap."

Warren

 

It's been awhile for me, but I now have a new sig quote.

Thanks Warren

 

ok guys, thanks for the info about bolt ins, now for the materials question?

i want to reiterate though, this car is for street and autox. also, i use del sol seats for now, and have them mounted w/ a hatch/coupe seat bracket which makes it sit extra low in my four door. The top of my shoulder is about at the top of the driver door panel, and im 6'2" (sitting up straight).
and about the bare metal, the cars already bare metal inside, so the danger of hitting my head exist anyway.
plus roll bar padding would be generously applied.
i dont care about the back seat, its been gone for years.

I have no plans in teh near future to actually road race the car, i dont even plan to do track days (sadly) b/c i dont want to take the risk of going off course at high speeds, pros do it all the time, so i will w/o a doubt eventually, its either that, OR simply not push teh limits, so whats the point? i'd rather do autox for now, IF i ever have enough cash to actually road race, i'll also have enough cash to re-do the cage for track competition.

FOR NOW, i simply want to stiffen teh chassis, but add as little weight as reasonably possible.
Ive heard bad things about chromoly too, like its very hard to weld it correctly, the welds may look good, but be "carbonized" (if i got the right word there) and in reality they may be very weak welds.

SO...
1. is DOM steek my best choice?
what tube dia and thickness should be appropriate for my purpose?

2. As far as design goes, im planning to basically copy the cages in the japanese ONE MAKE series races. i have footage of the mirage one make race, and civic one make races. they use a typical 6pt where the front bars go down into the floor right before the dash, and also have shoulder to ankle type bars which tie to the main hoop and the a-pillar to floor bar.

BUT, would i acheive more chassis rigidity by running the front bar all teh way down the a pillar to the firewall?

3. with a cage welded in place should the factory spot welds be strong enough, for example, where the rear subframe attaches to the unibody? I could imagine that being extra strong in some places could put extra stress on other places on teh chassis.
(is seam/stitch welding necessary?)

4. should the cage have welded connections at other points, (ie: top of main hoop to roofline, a-pillar bar to a-pillar, and b- pillars to main hoop)?

THANKS for the info guys, im glad i found this page.

-steve

 

legality isn't really an issue with me, and i do fully intend to have roll over protection (chromoly cage). convienece is no big deal, since i only drive the car maybe at most once a week.

EG8,

people who build roll cages tell me that DOM isn't a very good material. but if your not looking to do anything exotic that should be fine. a lot of people who criticize chromoly aren't fabricators, basically chromoly is industry standard for race cars and airplanes. It's all about using the right welding rod.

 

I guess I don't understand the need for a roll cage if you're not going racing. If it's extra stiffness you want, go with urathane bushings everywhere, big a$$ sway bars, and seam-weld everything.

 

Err? DOM ("drawn over mandrel") mild steel (e.g., 1020 or -25) is pretty much the industry standard. The issue with CrMo is that, if you weld it, it is supposed to be normalized - heat treated and cooled under controlled conditions - afterward. That just isn't practical for a welded in cage, given the budgetary constraints that most of us face with production-based cars. What are these folks recommending?? Not ERW, I hope.

Crome moly tubing (4130 and similar stuff) was originally created for aircraft frames, as I recall, and was typically brazed. Since the temperature required to do this is low enough to not change the molecular structure of the tube, it was a fine answer. This is NOT the case if it is TIG or MIG welded.

I am a *little* confused who I am replying to but, speaking generally, for autocrossing, any benefit from increase in stiffness MIGHT be offset by the additional weight penalty imposed - particularly in a non-slick class. In any event, the money might make the car faster if applied in other ways - practice being an excellent option.

Again generally, the only thing that makes less sense than putting a harness, bucket seat, and roll cage in a street car is putting a putting a harness, bucket seat, and an alloy roll cage in a street car (that only gets driven once a week). My being old might explain it but I am having a lot of trouble figuring out what a person could possibly do with a street car (once a week) that required that. Now, if he or she just cared that it looked like a race car, he/she could just save the extra $$, go with DOM mild steel tube (or muffler tubing for that matter) and just TELL people that it is CrMo!

Historically, Autopower cages tend to be on the heavy side (seems like they tend to round up on the tube diameter and wall thickness) but are a reasonble bolt-in answer.

Finally, if race belts ARE used in a street car, they must be tight! If they aren't, you just get a good running start in an impact before slamming into them. Your guts - since THEY have a good running head start, too - then slam into the inside of your bod, or each other. Eww.

Have fun!

Kirk

 

i think you are little bit confused about what can/can't be done with chromoly.

here's some info directly from the lincoln website.

Yes, you can TIG weld 4130 tubing up to .120" wall thickness easily with the techniques and procedures described in this bulletin. Answered are the top ten most frequently asked questions about TIG welding 4130 Chrome-Moly. These attached procedures apply to typical sporting applications such as experimental airplanes, racing car frames, roll cages, go-carts, bicycles, and motorcycle frames. The suitability of these techniques and procedures must be evaluated for your specific application.

Q. Can I weld 4130 using the TIG process?
A. Yes, 4130 Chrome-Moly has been TIG welded in the aerospace and aircraft industries for years. As with all welding, proper procedures and techniques must be followed.

Q. Do I need to pre-heat?
A. Thin wall tubing (< 0.120" wall) applications do not typically require the normal 300ºF to 400ºF pre-heat to obtain acceptable results. However, tubing should be at room temperature (70ºF) or above before welding.


Q. What filler material do I use?
A. Although there are several good filler materials, ER80S-D2, is one you should consider. This filler material is capable of producing welds that approximate the strength of 4130. ER-70S-2 is an acceptable alternative to ER80S-D2, as is ER70S-6, although the weld strength will be slightly lower.

Q. When I use ER70S-2 filler material, do I give up strength for elongation?
A. Yes. The filler material, when diluted with the parent material, will typically undermatch the 4130. However, with the proper joint design (such as cluster or gusset, for example), the cross-sectional area and linear inches of weld can compensate for the reduced weld deposit strength.

Q. Why is 4130 filler metal not recommended?
A. 4130 filler typically is used for applications where the weld will be heat treated. Due to its higher hardness and reduced elongation, it is not recommended for sporting applications such as experimental airplanes, race car frames, roll cages, etc.

Q. Can I weld 4130 using any other filler metals?
A. Some fabricators prefer to use austenitic stainless steel fillers to weld 4130 tubing. This is acceptable provided 310 or 312 stainless steel fillers are used. Other stainless steel fillers can cause cracking. Stainless filler material is typically more expensive.

Q. Do I need to heat treat (stress relieve) 4130 after welding?
A. Thin wall tubing normally does not require stress relief. For parts thicker than .120", stress-relieving is recommended and 1,100ºF is the optimum temperature for tubing applications. An Oxy/Acetylene torch with neutral flame can be used. It should be oscillated to avoid hot spots.


Q. Do I have to pre-clean 4130 material?
A. Remove surface scale and oils with mild abrasives and acetone. Wipe to remove all oils and lubricants. All burrs should be removed with a hand scraper or de-burring tool. Better welding results with clean materials.

Q. Do I need to back-purge 4130 material?
A. Backpurging is not normally necessary, although some fabricators do. It will not hurt the weld and may improve the root pass of some welds.
.

Q. Should I quench the metal after I finish welding?
A. ABSOLUTELY NOT! Rapid quenching of the metal will create problems such as cracking and lamellar tearing. Always allow the weld to slow cool.

More Information on TIG Welding Chrome-Moly 4130

Find out more about Lincoln Electric's professional line of TIG welders here
Or, check out Lincoln cut length TIG welding filler metals here

WELDING SPECIFICATION: Aircraft and Motorsports

GENERAL INFORMATION

Remove all oxides and burrs within 3" of weld area.
Acetone wipe to remove all cutting oils.
Assemble and tack weld in joint in a minimum of four (4) places with TIG.
Tubing should be at minimum temperature of 70ºF (room temperature.
TIG weld per parameters specified using Lincoln Square Wave TIG 175, 275 or 355.

The rules require that the car be caged. weight is a big concern also since it goes against full race cars.

 

Well, there you go - I would trust the folks at Lincoln to know their stuff. Interesting to learn that torch normalizing is accepted but then, I'm old and things change...

Thanks again for all of the FAQ info...

Kirk