Tech Inspectors/Experienced fellers, please help. Cage build questions/advice needed

[rc000e]

I have an E36 M3 that I am going to cage here shortly. I've had this car for some time, and a move has prompted I get it roadworthy again. The car has been stripped entirely, sound deadener removed, etc, in preparation for cage work. After extensive searching and reading, on forums all over the interwebs...I've got a few questions, that seem debated over the years. Of course, I want to build my cage to the most current standard, so that's the plan.

The cars intent: Will be HPDE until my schedule allows more. The car would likely be IP or GTS3, but my intent in the time being would be possibly an exhibition event or hill climb here and there.

The questions: I'm having a hard time determining which is the currently "preferred" standard on a few points.

-The first being, the rear attachment points. I've seen arguments for both the rear bulkhead and the frame rail/side of the shock tower. Can anyone confirm what the top cage builders are doing at this point? Any particular input you may have is also appreciated. If anyone has a particularly pricey/high end fabbed cage to post, do so by all means.

-Second, I've been debating plinth box versus floor plate. Though, I've pretty much debated myself that a reinforced plinth box, with a footer beneath it distributes load better than a tucked rocker tube does. I am always opened to discussion.

-Third, I'm wondering about A pillar reinforcement. I had intention of doing handformed A-pillar gussets, with a vertical bar. I haven't been able to confirm or not confirm, can you add gusseting from the A pillar to the body and it not be considered an attachment point? Classes of racing vary so widely, I'm trying to decide if I should do it or stray away from it for now.

-Lastly, is it pretty standard practice to contact a scrutineer via email possibly, to confirm in the "tacked up" stage that I'm not looking at any violations?


I want to make clear that this will by my first cage, but I've been a professional fabricator for well over a decade. I've seen many threads where people will plead that safety is important, etc and to see professional help. My issue is with the rule book and building a car with no specific purpose at this stage. I have a full fab shop though, all tools necessary to complete a cage attaining the highest standard. I just don't want to start off on the wrong foot. I've always prided myself in seeking the highest standard and attempting to always take advice from the best. Just looking for some friendly help here is all.

[thedizzle]

Here is a shot of my cage being built by Advanced Auto Fabrication (NW NASA Tech Inspectors). Hope this gives you some ideas. I don't know much about specifics but I do know these guys make a hell of a cage after seeing my M5 go end over end Joey Hand style at 140-150mph with the driver walking away with only a cut on his leg.

[rc000e]

Any chance you have pics from the trunk direction of the rear attachments?

I've debated the nascar door bars versus a double bent X. That's still up in the air with me...as it seems to be debated what's necessary for road race conditions versus weight, etc. I like how they stitched the lower door bar to the door sill. Guess whatever class you race allows chassis stiffening... This has been something I've been trying to consider. Stiffening elements are allowed in some classes, but not others. Would be something I'd like to incorporate, but would hate to regret it later.

[thedizzle]

http://www.nwbmwclub.com/RacingM5 for more pictures

[rc000e]

Thanks for that.

Hopefully some others can chime in on my questions.

[timsev]

IB4 "those welds aren't robotic and perfect bro, unsafe"...

[thedizzle]

IB4 "those welds aren't robotic and perfect bro, unsafe"...

Most builders don't have their cages tested, these guys had 2 or 3 last year alone with all drivers walking away and the cage/safety equipment doing the job it was designed to do.

[rc000e]

No chance of any video on that wreck is there...that had to be a wild one.

[Massive Lee]

Hmmm... Full cage in an HPDE car? Will it be trailered to the events?

[clopez95m3]

Hmmm... Full cage in an HPDE car? Will it be trailered to the events?

I've thought about doing the same for DEs, a roll bar isn't enough for me anymore. My goal is to keep it legal in BMW prepared class and also SCCA improved touring. Even though an E36 M3 isn't an IT car it can be raced in one of those newer classes (STU maybe?), anyway the point is that if I ever sell it, someone can race it w/o altering the cage which is a huge PITA.

If that's also your goal, then stick to the BMW club rules for cages as that will be the lowest common denominator. I haven't looked at NASA rules lately so I'm assuming the above cage is legal having 4 pts just in the rear (from the pics). BMW club allows 6+2, the 2 being foot protection. The above cage would not be legal, also welding a tube on top of another without intersecting them is also not allowed (the rear horizontal plane X with the smaller tubing).

As to plinths vs floor plates that's a good question. The cage builder we use prefers floor plates so that's all we've done, for the main hoop it is tied in 3 planes with 3 plates welded together. My concern with plinths is wether there's a situation where they could get crushed.

A-pillar reinforcements, another good question. You can run a bar straight down to the forward down tube attachment plate, you can do a taco gusset and reinforce the bend, you can also weld in a reinforcement tube between the two tangents of the bend. What I wouldn't do is tie a plate from the cage to the vehicle's a-pillar as you have just limited yourself as to what classes you can run. In BMW club it puts you in Mod ($$$). If NASA GTS allows it then that's definitely something I'd do.

The rear tie in also a good question, we've done the rear bulkhead for Prepared class and to a built up rear shock tower for Mod, E36s are especially weak in that area so a built up stronger tower is necessary IMO. It's also done to run rear coilovers which are Mod only legal (unless the car already had rear coilvers (stock) to begin with).

I'd definitely contact a scrutineer if you're concerned about legality, I've gone out to inspect cars as they were being built to answer questions. I think only once did I have to fail someone's cage and it was because they used thinner walled tubing than allowed by the rules. You can do it for optional tubes but not for the required ones.

Carlos.

[Massive Lee]

I am glad the OP is thinking about his safety, as well as strengthening the shell, even for an HPDE car. Hat off for his commitment. But my preceding remarking was more about driving a caged car on the street. Even with padded cage, it remains a very dangerous environment as you won't be wearing a helmet around town and on your way to the track. Or will you? ;-)

[Damon in STL]

I was on the "No Roll Cage!" side of the argument for a car driven on the street up until a couple of months ago. What changed my mind is that we bought a Jeep Wrangler Unlimited last fall. In the Spring I took off the hard top and started looking at the cage that is stock from the factory. The only real difference is that parts of the cage are covered with either some plastic parts along the B pillar area or (the area up high between the A and B pillars) is covered with the same high impact foam AND a fabric material which zips over the foam and keeps it in place. So, now I'm thinking...."why can't the cage be covered with FIA foam pieces in a street driven car?" camp.

Damon in STL

[clopez95m3]

I am glad the OP is thinking about his safety, as well as strengthening the shell, even for an HPDE car. Hat off for his commitment. But my preceding remarking was more about driving a caged car on the street. Even with padded cage, it remains a very dangerous environment as you won't be wearing a helmet around town and on your way to the track. Or will you? ;-)

Oh that. ;-) Yes definitely a concern and a risk that one has to weigh. If it's too much risk then yes trailer the car.

I believe there's still a handful of racers that still drive their race cars to the track, I recall one is in Canada. :-)

Carlos.

[TeamDFL]

The rules make things difficult for cages with plinth boxes. Avoid them if possible. Tech inspectors frequently choose to ignore this requirement but that won't happen forever.

From BMW CCA clubracing 2014 rules, Appendix A:
"20. Alternate Design/Construction
A. Alternative roll cage design and/or construction may be accepted with the designers and/or constructors or structural engineer's certification that the cage meets or exceeds the specifications described herein.
1. Certificate must include the certifiers name, address, business name, business license number, and professional credentials.
2. The certification document must be attached to the vehicles logbook.
3. If “plinth” boxes are used the constructor must include in the certification the structure includes a load distributing bottom plate"

[rc000e]

Massive and Clopez, thank you both for your responses.

Massive...as with many "track day" cars, the car will maintain lighting, glass, etc and in turn be a legally operable street car. That said, the amount of street use the car sees would be likely very limited, if at all. I have a pretty built Z06, as well as an S2000, which are my fun street cars, so this car would be mainly track use only and would be trailered. I bought the M3...it's an icon car in my opinion, and I wanted to build/keep it indefinitely for track use mainly. At most, I may drive it to caffeine and octane or something along those lines, but I would equate the danger of driving in a fully padded/caged BMW as equivalent to these folks that drive motorcycles helmetless. I would consider that to be a stretch even.

Clopez...all good info, thank you very much. Much like the point you made, regardless of DE use or exhibition use now, resale (likely I never will, but you never know), as well as future use makes me want to build the cage to suit as many potential uses as possible. I DO want to avoid MOD level classes though, as I would never jump directly into that game first of all, nor do I foresee making that investment/commitment given my life schedule. I think I will stray from the Apillar reinforcement for certain.

TeamDFL...I'd have no issue with the certification, so that doesn't dissuade me really.

My issue comes with the rear attachments. I am running coilovers on the rear, and stressing that tower beyond it's originally designed intent...not to mention, it seems those towers had their weakness as it was. So, given the points you make, maybe I'll go that route as it addresses my current use, but doesn't restrict me.


It appears, based upon what I'm seeing I'm going to make the plinth boxes out of 3/16, the gussets out of 18 gauge and the tubing will be 1.75 x .095 DOM, all TIG welded, except maybe the plinth to the floor and plinth itself.

[robbo mcs]

I am glad the OP is thinking about his safety, as well as strengthening the shell, even for an HPDE car. Hat off for his commitment. But my preceding remarking was more about driving a caged car on the street. Even with padded cage, it remains a very dangerous environment as you won't be wearing a helmet around town and on your way to the track. Or will you? ;-)

I understand your comments about street driving with a cage, and technically you are correct.

However, I come from a rally background, which I know is not as big in the USA as in Europe or my part of the world. However, in rallies you are forced to drive your car on "transport" or "liaison" stages on public roads. I have driven probably 10,000m like this over the last 10 years. I am one of thousands of cars competing in these rallies. I must say, I have never once heard of anyone who was injured in an accident in such stages due impacting their head on a roll cage. There have been serious accidents, just last year once of the WRC cars was written off on a public road stage.

I am not saying you are wrong about the theoretical risks of driving on the street with a cage, you are correct. However, I think we have to keep it in perspective, and risk stratify etc. In the big scheme of things I don't think it is necessarily so bad.

BTW there hasn't been a good cage build thread for a while. Nothing like it to get people arguing about the merits of nascar vs x-bars, plinth vs floor plates etc!!!

[JohnnyBgood95]

I am glad the OP is thinking about his safety, as well as strengthening the shell, even for an HPDE car. Hat off for his commitment. But my preceding remarking was more about driving a caged car on the street. Even with padded cage, it remains a very dangerous environment as you won't be wearing a helmet around town and on your way to the track. Or will you? ;-)

I daily drove an H3 car for some time. My head was so far away from the cage that IF my head would/could have hit it, I would have had to worry about more problems than a head injury.

[NeilM]

I daily drove an H3 car for some time.

H3? Nice track car! ;-)

My head was so far away from the cage that IF my head would/could have hit it, I would have had to worry about more problems than a head injury.

Really, with a full cage? What about the bars above the doors? And how much do you suppose the seat or its occupant can move in an impact? Have you ever seen sled test videos?

A little anecdote: Last season a good friend of mine in his fully caged E36 M3 track car (trailered) had a pretty violent off at Mid Ohio, with major damage to his car. His helmet hit the cage main hoop's unpadded diagonal bar hard enough to crack the helmet. Pretty much rang his bell too. He briefly lost consciousness, then was confused and disoriented, and was taken to hospital for observation. He was released later that day, but still has no recollection of the accident.

Now imagine that on the street without a helmet.

I'm not saying one should never drive a caged car on the street, only that it's a decision to be made with eyes wide open and without rose tinted glasses.

Disclaimer: My own track car has a roll bar (half cage) and is driven to the track, but rarely on the street otherwise. The entire main hoop and diagonal have high density SFI 45.1 padding down to the harness bar level.

Neil

[99MPower]

just FYI... the cage design that was posted earlier would be immediately sent to GTS. Too many attachment points, tied into the body, etc. NOT a prepared legal cage for BMWCCA.

My IP level cage in my 99 M3

http://forums.bimmerforums.com/forum...t=gts3+ip+lite

some other IP level cages

http://forums.bimmerforums.com/forum...s&highlight=IP

http://forums.bimmerforums.com/forum...d&highlight=IP

Need to get into the BMWCCA club racing rule book, and read the cage design rules. GTS is wide open, you could do whatever you want, so if u want to run in IP, you need to build the car to IP rules

[rc000e]

As you stated above, it was an unpadded diagonal. Also, the positioning of the diagonal could have much to do with it.

I've ordered the material from the mill, so here's the verdict.

I'm doing footers, not plinths as it turns out. As of now I'm doing x-bars not Nascar side impact, but I still may change that because of the PikePeak rule structure. I've always had a dream to drive a car to Pikes and compete...win or lose...just basically make a good showing and not die...haha. I'll be doing a myriad of gussets with dimple dies in 18 guage. I'll be going to the rear attachment point using a footer plate and a "node".

The issue appears to be, that I have to use 3/16's footers to meet the PikesPeak rules, which exceeds the BMWCCA ruleset. I don't see anyone require a diagonal roof bar though, as that appears to be considered "extra non required reinforcement bars". Anyone disagree with that, or am I missing a sentence somewhere??

[rob22sf]

if tony has time, im sure you can email him some questions.

http://www.tcdesignfab.com/projects.php

[clopez95m3]

The issue appears to be, that I have to use 3/16's footers to meet the PikesPeak rules, which exceeds the BMWCCA ruleset. I don't see anyone require a diagonal roof bar though, as that appears to be considered "extra non required reinforcement bars". Anyone disagree with that, or am I missing a sentence somewhere??

Most rulesets state minimums so yeah a thicker foot plate is totally fine. Also I'm not aware of anyone requiring diagonal roof bars for club racing, they may be added of course.

Carlos.

[rc000e]

Well, just got my delivery of materials today, along with more sets of dies and whatnot. I am in position, just have to do some accurate measurements to model the cage in bendtech. That's going to be another little hurdle. I am comfortable with the software, but I'm unclear about how to measure the car, to translate to the software. It seems the assembly functions use center to center measurements, but using outside wall measurements seems to allow me to measure the car itself and build the tightest cage. I don't know...I'll figure it out as always....

Is it wise to model one bar at a time, then build the cage in the software, as you build the cage literally? Also, I've seen some options on using outside measurements versus centerline.

Anyone use bend tech here that can talk about their workflow and how they best utilize it and measure it out?

[jhott66]

OP, I am in the process of having a custom 4-point rear rollbar/cage fabricated.
I will post pics when complete.
The car competes in NASA TT.

We decided to mount the rear parallel down tubes at the rear bulkhead. A "x" connects the top corners of the main hop with the rear bulkhead.
The main hoop is attached at the triangle notch off the floor; between the rear seat hump/fuel tank hump and the exterior wall. A small triangulated structure is fabricated and welded to this area and the hoop tubing welded to this.

Good luck.

[rc000e]

Interesting...post pics when able. I have construction on my shop schedule to begin August 4th...doing two cars at once. Fabrication Menajahtwa!!