My roll cage/harness bar selection

[jakob66]

I built this in June this year but had no time to report.
Being more and more often on the track the stock seat and stock seat belt didn't fit in the picture anymore, not enough support, not save enough, not for the track.
Just switching to a race seat (w/o seat air bag) and with a 6p harness is not a good idea either. The weakest link will be your neck and when you get into a Hans device you have no room in case of a collapsing roof and now your spine is being targeted. This goes on and on. So I decided (and many before me on this forum) to go all the way with a seat, 6p harness, 1/2 cage and Hans devise.

So now I was looking for a bolt-in 1/2 roll cage. It should do the following (not in the order of importance):
#1 being 100% reversible
#2 easy to take in and out
#3 compliant to NASA cage rules in case I want to expand the cage to the front to and join real racing
#4 if possible stiffen the chassis
#5 most important (being a bolt-in cage) not to punch through floor in case of a roof 'landing' (that's a weak point of many bolt-in cages)
#6 I'm 6'2" with tall torso so custom height of horizontal harness bar (to fit the Profi XL seat)
#7 should not cost an arm and a leg

There are many good cages out there but somehow they didn't fit my list. So I decided to make my own cage.
I'm in a unique situation as I have access to Pro/E and AutoCad, lasers, press brakes and TIG welding in my shop so this made this decision a little bit easier. The first thing I had to do was studying the NASA cage rules to set the minimum specs for my car.
https://nasa-assets.s3.amazonaws.com...282/2015.3.pdf .
So based on the M3's weight I knew I had to go with DOM 1.75" x 0.120. The rules spec the bent angles on the tubing, determines the rear cross bars, the horizontal cross bars, size of flanges and amount of bolts. Pretty straight forward.
Next thing was to determine the dimension in the car and that was the time consuming part!
I took the interieur off (both stock front & rear seats, carpet, everything in trunk etc) and installed my Recaro seat
(no slider to gain headroom for helmet!). Then I used 1.75" cardboard tubing and lot's of painters tape to fit a
mockup cage into the car. Would have been much easier to get a BMW 3D model but you know...
I then simply took those dimensions into AutoCad.
Important to mention is that I decided to use 2 more gussets to sit like a bridge on top of rear seat beam to make this cage a 6 point bolt-in, see #5. Purpose of those additional mounting points is to spread the loads coming from a roof impact to make sure the floor brackets cannot sheer through floor panels.


I sent this drawing to a well known cage builder who bent me the main loop. He did a very nice job and met the main dimensions. I lasered all flanges in my shop in 0.25", more than enough. As I had to fit and tack-weld all the tubing inside the car I covered the interior with weld curtain to protect fabrics, worked fine.


For the rear cross bars I wanted to go all the way to the rear strut towers and with a wide angle (angle A ) as this -besides the points you're connecting to- determines the strength front to rear of the cage. The rear strut tower braces utilize the stock M12 and M10 bolts per flange. A solid left/right cross bar is a fine base for the rear cross braces.
All this need to be connected via double bolted tube connectors. I got those from Summit racing.


Once I notched & tacked all tubes in place I unbolted the cage and took it to the welding shop. My buddy Tim TIG welded the entire frame except the main flanges for the floor. I expected a lot of warping due to heat so I wanted those welded after the straightening process followed by a test fit in the car.
A good paint job was the final touch. I didn't want it flashy, more like a sleeper so I choose black. With seats still out I had the cage bolted in within 30min. To keep the shoulder harness in place I bought drive shaft collars for ~$15/ea on Ebay. Those could be black anodized too (? ).




Between roof and B pillars there's less than 1/2" space, I tried to make this cage as wide and high as possible.


Sorry for the bad quality of the pictures and another sorry for my bad taste of the yellow window net in the back. I should have ordered it in any other color . In addition my carpet cutouts for the floor flanges didn't go that
well but that's easy to fix. A real 'rear seat delete cover' would certainly compliment the looks and 'yes' a 2nd Recaro will be my Christmas gift.

It's hard to qualify the stiffness of my chassis -now with a cage- as I don't have a chassis test bench but I could swear that this thing is much stiffer now and I feel so much saver.
The entire cage, harness bar and the rear visibility in conjunction with my seat turned out to be perfect (perfect for me).
In late fall I will put a cage package kit together, in case someone is interested.
My car will be at VIR Oct 10/11 and at Road Atlanta Nov 21/22.
Cheers!

[SYT_Shadow]

This looks extremely interesting

It's sad that known shops don't build harness bars like this to hold your 6pts in place. It's safer to run race seats and 6pts even if you don't have a welded in or full cage

Breyton-Kraus has a similar solution but this has a top loop which I prefer

If you build a 'package', I'm interested

[ThunderMoose]

great job!

[jakob66]

Originally Posted by ThunderMoose

great job!

Thanks!

[M3 Number 86]

I think the GTS cage bolts to the rear section as well but does not go all the way down.

I would love to do a package too but mine is sedan dammit.

I like the yellow net!

[jakob66]

Originally Posted by M3 Number 86

I think the GTS cage bolts to the rear section as well but does not go all the way down.

I would love to do a package too but mine is sedan dammit.

I like the yellow net!

That makes me feel better. My wife thought my color taste got off track
The M3's floor panel really has nothing to offer to hold a cage and that's why the GTS cage takes the rear seat beam. By bolting to the same beam and using the stock seat belt bolts on the floor I was hoping to get the best from both worlds. In addition I don't have to argue with a tech on the track as the NASA cage rules ask for floor brackets.

[///Mobbin]

Very nice work, thanks for sharing! I'm 6'2" also and have been curious if there is a bolt-in solution that might work for me. What was your second choice if you were to purchase a half-cage?

I'm also interested if you think about selling these.

[M3 Number 86]

Originally Posted by jakob66

That makes me feel better. My wife thought my color taste got off track
The M3's floor panel really has nothing to offer to hold a cage and that's why the GTS cage takes the rear seat beam. By bolting to the same beam and using the stock seat belt bolts on the floor I was hoping to get the best from both worlds. In addition I don't have to argue with a tech on the track as the NASA cage rules ask for floor brackets.

ah I see...yeah I meant *seat don't know why phone corrected a correct word. Damn it's not even autocorrect anymore, it's predictive text!

Did you use any other pieces to reinforce the mounting points?

I've seen way to many holes in people's bolted cages to the floor. Um, why do I see asphalt through your floor?

[jakob66]

Originally Posted by ///Mobbin

Very nice work, thanks for sharing! I'm 6'2" also and have been curious if there is a bolt-in solution that might work for me. What was your second choice if you were to purchase a half-cage?

I'm also interested if you think about selling these.

Thanks for compliments.
I really can't/won't speak about the other cages. The OEM GTS cage ($!) and Alekshop's cage are nicely done. However, both don't check all my points on my must-have list.
I will have my last event at the end of November (MVP Atalanta). After that I have the time to put a kit together.

[surlynkid]

Very nice to see it TIG welded. The Alekshop unit is just a direct knock off of the GTS unit.

[jakob66]

Originally Posted by M3 Number 86

Did you use any other pieces to reinforce the mounting points?

All brackets/flanges are laser cut 1/4" steel. Both floor plates have 3 additional holes and use a 3 hole plate underneath(outside) the floor to clamp the floor plate. I haven't yet drilled holes on mine and used only the M12 stock seat belt bolt but others might want to drill so I added the holes.

[rzm3]

Any pictures of how this is mounted in the back? TIA!

[jakob66]

Originally Posted by rzm3

Any pictures of how this is mounted in the back? TIA!

I don't have any on hand but can make some. I'm out of town till Sunday so somehow next week.

[DC_Monstars]

So this is NASA "approved"? Wish i saw this earlier would have liked to seen it in person at VIR.

[jakob66]

Originally Posted by DC_Monstars

So this is NASA "approved"? Wish i saw this earlier would have liked to seen it in person at VIR.

To my knowledge there's no such sticker that says 'NASA approved' if that's what you're asking. In HPDE/TT there's not even a cage required.
However, if you have a cage it should be according to the NASA rules which my harness bar/ half cage is and it will pass the tech inspection.

[SYT_Shadow]

Please take as many pics as possible of the mounting points

[NoSHAM3]

I'd be interested in one of these cages as well! Great work here.

[///Mobbin]

Sorry I have a lot of follow-up questions (still loving this setup btw!).

What floor mount adapters did you go with and how are you attaching the lower harness sections? Then, what Schroth harness did you choose (I do see that it's Hans compatible)?

Last question, any comments on the comfort of DD-ing a Recaro Profi XL?

[jakob66]

Originally Posted by ///Mobbin

Sorry I have a lot of follow-up questions (still loving this setup btw!).

What floor mount adapters did you go with and how are you attaching the lower harness sections? Then, what Schroth harness did you choose (I do see that it's Hans compatible)?

Last question, any comments on the comfort of DD-ing a Recaro Profi XL?

If you look at the first picture with the sketch you can see the right floor flange. I can send more info once I'm back home. The bolt that holds the stock seat belt rail has been utilized.
I used the Schroth Profi II Flexi-Belt Camlock which is Hans compatible and I use a Hans 2.

The Profi XL fits me like a glove and once in I can ride all day long.
Getting in and out is kinda tricky. I kept the stock seat belt so DD-ing for me is ok. However it's totally subjective.

[///Mobbin]

Originally Posted by jakob66

If you look at the first picture with the sketch you can see the right floor flange. I can send more info once I'm back home. The bolt that holds the stock seat belt rail has been utilized.
I used the Schroth Profi II Flexi-Belt Camlock which is Hans compatible and I use a Hans 2.

The Profi XL fits me like a glove and once in I can ride all day long.
Getting in and out is kinda tricky. I kept the stock seat belt so DD-ing for me is ok. However it's totally subjective.

Sorry, I was a bit unclear. I actually meant what floor mount adapters did you use to mount the Recaro seat?

And thanks for the Schroth and Profi info!

[jakob66]

Originally Posted by ///Mobbin

Sorry, I was a bit unclear. I actually meant what floor mount adapters did you use to mount the Recaro seat?

And thanks for the Schroth and Profi info!

Ah, sorry misunderstanding. I have the MachtSchnell floor mounts and the Recaro brackets but w/o the sliders as I wanted to gain head room. The 2 bolts that hold the seat (on driver's seat right side) to the Recaro brackets are a PITA to install as you can't slide the seat. But it's worth it.

[///Mobbin]

Originally Posted by jakob66

Ah, sorry misunderstanding. I have the MachtSchnell floor mounts and the Recaro brackets but w/o the sliders as I wanted to gain head room. The 2 bolts that hold the seat (on driver's seat right side) to the Recaro brackets are a PITA to install as you can't slide the seat. But it's worth it.

Nice, thanks, the MachtSchnell mounts seem quite popular. I'm curious if I could make it work with the sliders as I would consider swapping back to OEM seats in the off-season and the sliders would make that easier. I do understand this would limit my helmet room though, will have to think about that some more. Maybe just running them all the time is the way to go.

Here's a seat-install video that EAS put together if anyone is interested:
e92 Recaro Pole Position Install Video