Roll cage design lessons learned?

[Broncobowsher]

I can recount a story of a Bronco owner here in AZ who wrecked on the freeway. Bronco was caged, NOT tied to the frame. Seats and belts were tied into the cage. At freeway speeds ran into the center wall. Bronco came apart. Axles out, engine out, cage came off the body. All that destruction absorbed energy, the key to any crash is spreading the energy out. Total injurys, had a hole poked in his leg from the turn signal lever as the cage was separating from the body.

Just building a solid structure isn't going to make it safe. Don't rely on the crumple zone of the other car, because concrete doesn't have a crumple zone.

 

[panchorelli]

The one thing I noticed in all the photographs is the rear quarter panels do not seem to crush/bend/or warp. Why not mount the roll cage to the rear quarter panels?

A roll cage bolted to thin floor panel sheet metal is as good as the the sheet metal is real thick and capably of supporting a load....not really IMO.

Think frame tie-in into your design. You can still bolt (grade 8 or better bolts) it to the floor pan, think support from underneath the floor pan to the frame.

Think rock slider/hard mount nerf bar idea that protects your rockers/giver you a step and ties the cage to the frame all in one.

 

[TonyPDX]

One thing to watch for if your looking for head clearance is don't go too wide. When I built the 1st cage on the 72 I went as high and wide as possible. The cage isn't leaning against it but running topless the door frame rattles on the cage on bumpy roads. One of these days I'm gonna put a piece of rubber up there.

Thanks, that is good point. Currently, it is designed to tuck tightly into the corner of the headliner and I will have a tie-in point for the soft-top door frame so that should not be an issue.

 

[TonyPDX]

... Main hoop also bolts to the B-pillar.

I am not planning a frame tie in at this point either but a stout tie in to the upper bed rail at the B and C pillar is. How did you do yours and would you do it the same if you did it again?

Thanks, Tony

 

[TonyPDX]

The one thing I noticed in all the photographs is the rear quarter panels do not seem to crush/bend/or warp. Why not mount the roll cage to the rear quarter panels?

I noticed this also looking at roll over images. So, I am going to tie it into the upper bed rails at the B and C pillars which will help a lot to resist racking and deforming the floor to the point of 'failure'.

 

[panchorelli]

I noticed this also looking at roll over images. So, I am going to tie it into the upper bed rails at the B and C pillars which will help a lot to resist racking and deforming the floor to the point of 'failure'.

I'd love to share/swap ideas with you. I'm doing the same thing, incorporating the seat belts while skirting the hard top and mounting it to the B/C pillars. BOOM.

 

[bamabaja]

Anyone tied tube doors to the cage, or otherwise strengthen the tube doors for side impact purposes ?

 

[nvrstuk]

I tied mine into the rear qtrs back in '01. Not extremely structural but its there...I didn't have my BC qtr guards on till a couple years later but on my "list" was tieing them in somehow...since my build with struts, WB stretch, etc is tieing my tube fender flares into the strut tower with 1 1/ 4" DOM for a bit of rigidity...where do you stop...?

 

[jim3326]

I am not planning a frame tie in at this point either but a stout tie in to the upper bed rail at the B and C pillar is. How did you do yours and would you do it the same if you did it again?

Thanks, Tony

I just put a tab between the hoop and bedrail to fill the gap, 3/8" I think, and a plate inside the rail.

 

[TonyPDX]

I'd love to share/swap ideas with you. I'm doing the same thing, incorporating the seat belts while skirting the hard top and mounting it to the B/C pillars. BOOM.

Hey Panchorelli, it seems this concept of pursing the tubes as far up and out as the hardtop w/headliner will allow is catching on. (I am far more worried about smacking my head than getting crushed based on the research I have done.) I am working on getting quotes from two guys in the NW who have built cages before.

My biggest open items at this point are:

1. A-pillar solution, I may just cantilever it similar to BC Bronco's or do a kick panel plate up to a dash top mount.
2. Tie in to the bed rail at the C and B pillar

 

[nvrstuk]

Small cut in the dash and the A hoop allows unobstructed access to the cab w/o an "S" curve. The feet are welded to my rock skis (frt and back) and then my body mount is replaced with a 2x2 tube which is then welded to the front legs and is bolted thru the original body mount and another one directly on top of the frame rail. Probably hard to follow but it's secure...

 

[68ford]

For A pillar, why not run them extremely close to the windshield frame and behind the dash. Have the dash bolt to the cage and be a little close to you. Makes it easier to reach anyway. Looks a lot cleaner.

 

[68ford]

https://goo.gl/images/Zym7dT

Truck a pillar tubes, just cover with interior.

 

[JSmall]

For A pillar, why not run them extremely close to the windshield frame and behind the dash. Have the dash bolt to the cage and be a little close to you. Makes it easier to reach anyway. Looks a lot cleaner.

That was my thoughts. Behind the dash and the main hoop (A and C) bends towards the center of the Bronco at the body line. That allowed me to get the hoop as high as possible and still fit under the hard top.

A and B will be tied into the rock slider and C will be tied to the frame. I'm still adding bracing, but don't want to go too far until I get the suspension seats in there.

In the pics you can see how close the cage is to the windshield frame and where it is in relation to the hard top. I'm within a 1/4" of contact in all directions. High and tight

 

[68ford]

Jsmall, that look a hundred times better than the cage going in front of the dash with the S bend. Very nice

 

[nvrstuk]

Looks great Jaromy!

 

[Hozr]

Cages! Yay!

So many opinions and none are right! J/K only MOST are wrong or at least ill informed of the design intent.

Look at motorsports regulations before you do anything. If there is one place cages actually get tested and used it's there.

The Biggest safety items off the top of my head are:

No crush bends. If you are using an exhaust bender or H/F bender, well....just don't.

Single piece main hoop. The "B" pillar hoop. This is the foundation of your cage and safety. It should be as close to vertical as possible with smooth bends (within bend radius spec for tubing diameter and wall thickness) and made of one continuous piece of tubing (notice I didn't say pipe).

Triangulation. Triangulate out to the anchor points. Tubing terminations should be supported all the way out to anchors and main diagonal bars should be as straight as possible. Tubes that terminate unsupported in the middle of another tube WILL deform that tube.

"S" bends or "crumple zones" - Just don't...

I can go on for days, weeks, months....Only you can determine the level of safety you want and how much cage you need for that goal. Please don't incorporate and idea because it "looks" cool. Research what works and go from there.

In my cage design I sacrificed a few things here and there because I know how I will use the truck. I don't need a competition cage but I also know if it ends up on the lid it won't collapse.

 

[68ford]

Google "trophy truck" then click images. Use them to get ideas, that's as good as it gets.

 

[Broncobowsher]

There was a circle track series about 15 years ago (IMSA?) that had cars built so solid that when they hit the wall it would break a ball joint and kill the driver. But a new ball joint in and a new driver and go back to racing. It was getting bad. They last a few drivers in a single year, and the cars were essentially unharmed and usable after a crash. Rules changed. Bars were removed. Design changes mandated. Cars would bend now. It worked, drivers lived through wrecks. The car would need a lot more work, but at least the driver wasn't dead. This is a lot closer to how street driving happens. Hard walls, other cars involved. Trophy truck, when they crash it is just a really fast roll over across a soft desert floor most of the time. Not smacking into a concrete wall. With as solid as a trophy truck is hitting a solid wall is going to be a very bad thing.

I've seen caged cars go through a commercial car crusher. It doesn't even slow it down. They fold the same.

 

[68ford]

Broncobowsher, we are just going to not totally agree on some of your statements. I have seen in car camera of trophybtrucks and class 1 cars rolling at 110 plus mph, bad rolls and the chassis almost seem like nonharm was done and the camera never even comes out of focus. But regardless you comparing it to running into a solid wall, I am certain that it would be impossible to make an EB survive half as well in the same accident. Obviously it is impossible to remotely duplicate a TT chassis inside an bronco, but I would say it's a great place to look for design ideas when about 99% of EB cages out there are garbage.