Custom Roll Cage Main Hoop Fabrication

[tperazzo]

Ever wonder what it takes to make a custom roll cage? I found out the hard way that it isn't easy, but a fun project nonetheless. This was my first attempt and its on video. Warning: it involves swimming pool noodles and elec conduit!!!

So far I have the main hoop formed and trimmed the way I want it to fit to my car. Future plans are to connect the back stays to the rear shock tower gussets that I fabricated. That thread is here:
https://forums.pelicanparts.com/porsche-911-technical-forum/1013546-rear-shock-tower-gussets-fabricated-coilovers.html


I know some spec classes don't allow tubing to extend outside the cockpit, but my car isn't stock anyway.

I'm also going to connect the main hoop to the B pillars with a gusset plate to further improve torsional rigidity. I evaluated relative torsion rigidity improvements for 1) seam welding, and 2) front shock tower braces. That thread is here:

https://forums.pelicanparts.com/porsche-911-technical-forum/1015116-seam-welding-works-before-after-testing-video.html

I will repeat that test for the half cage when its complete.

I'm also going to add some diagonal bars from the main hoop down to the torsion tube area that I've already braced to the body. So that should be interesting.

I may fabricate some removable door bars if they improve chassis rigidity, we will see.

Here are a few photos:



Here's the vid:
https://youtu.be/TXaCOYAbwVU

[Walt Fricke]

What is that community workshop? Looks like an outstanding resource.

Your clearances should allow you to reinstall the upholstery and headliner, if so inclined. I got mine back in on my full cage with the barest of margins, and had to modify some of the steel stays.

My biggest miscalculation was the repositioning of the stock shoulder belt. I made a new mount for the retractor, but neglected to think about the D ring up on the B pillar, other than that I could get the bolt in. Turns out, the D ring (really more a triangle) couldn't swivel to where it needed to be, so the angle of the webbing would be wrong. I switched the stock type belt to a manual adjust, but after years of a retractor this got old.

[tperazzo]

Hi Walt,
You bring up some good points. My car won't have the stock interior parts as it will remain mostly stripped out plus a little sound deadening here and there. I will begin positioning the seatbelt mounts before I start welding the cage in. Thanks.
The community workshop is convenient for me as it's about 15 minutes from my house. That is where I machined the wooden hammer forms to shape the longhood section and fender extension sections. I will be using this shop more for some custom parts in the near future.
It works just like a gym membership. Some classes are required to use the fun tools. Check out their website:
www.urbanworkshop.net
Thanks,
Tom

[tperazzo]

Now that my lowered seat position is finalized I welded the harness bar in. I did have some trouble getting the fish mouth coping to fit the main hoop right.



In one of the photos you can see a paper template with red circles. Next week I hope to make these gusset plates with speed holes for extra chassis stiffness.

Soon, the welding will be done!

[Sebscst]

One thing I’ve noticed on my car which is a stripped lightweight is I’ve cracked the windshield. I have a carbon roof. I think my A pillar is flexing. I like your mock up on the b pillar stiffener add one on the A pillars. Nice build.

[3rd_gear_Ted]

Next design question to answer.
If you have bars across the driver seat opening, your design needs to accommodate the way you like to get in and out of the car.
Do you want to step into the car and pull your other leg inside over a straight bar?
Or do you like to put both feet inside first and slide into the seat over a bar angled forward?

I angled my bar for the slide in method cuz I'm a big guy.
Also added a straight bar of much larger diameter across the very bottom portion of driver door opening, this aligns across with my lower torso and is the point of impact in a race track, T-bone scenario by another car.

Fiberglass doors allow the bar to have a angled bend outward into the door cavity for better impact protection.

Side impact is most likely to occur as compared to an end over end roll over.

[tperazzo]

Originally Posted by Sebscst

One thing I’ve noticed on my car which is a stripped lightweight is I’ve cracked the windshield. I have a carbon roof. I think my A pillar is flexing. I like your mock up on the b pillar stiffener add one on the A pillars. Nice build.

This is interesting and sorry to hear about your cracked windshield. Does your car have a full cage? Curious to know more about your car.

I think the A pillar area is likely going to be the weakest area of my car too, however I'm not going to have any cage their to connect the A-pillars with.

I am going to do more rigidity testing once I get my cage welded in.

[tperazzo]

Originally Posted by 3rd_gear_Ted

Side impact is most likely to occur as compared to an end over end roll over.

I totally agree that side impact is more likely than roll over.
I plan to make my door bar removable so I can take it on and off during track days. I will experiment with how difficult it will be to get in and out, but I'm thinking I will try the angled down bar first. I also left the steel doors with crash restraint in on the drivers side only.
We'll see how it turns out and how I end up using the car in the future.

[Walt Fricke]

SCCA and, I think, FIA have some design standards for removable bars. Worth a look.

[T77911S]

I assume you curved the horizontal bar that goes behind the seat for room for the seat.
problem is you created a weak point for that bar to crumble if you have a side impact.
that bar should be straight and it should tie in with the diagonal bar.

[piscator]

Thanks for the thread! It's very interesting to learn about this.

[ClickClickBoom]

What kind of tubing bender?

[tperazzo]

Originally Posted by ClickClickBoom

What kind of tubing bender?

It's an older JD2 or JD squared bender. I really like it once you get the hang of it. I would highly recommend.

[Walt Fricke]

T77 - most cage rules for sedans in road course racing do not require a cross bar. Some cages are built with a half-bar, whether curved or not, just for mounting the harnesses.

All require the diagonal bar, to prevent racking of the main hoop.

Yes, a straight bar is going to help in a terrific side impact. If a guy is worried about that, but the seat is going to be in the way of a straight bar, something else could be designed.