Roll Cages, Internal, External, Design, Safety
Roll cages....many of us have them, some do not. Some of us have them and don't realize the inherent weaknesses of a "factory" roll cage or an improperly built cage. Depending on how hard you wheel or expect to wheel, what you have or not have now may be perfectly fine. The harder the trails that you wheel or the harder the obstacles that you want to try, the more you are going to be wanting the safety of a good roll cage. It is usually not a matter of "if" you roll, but more of "when" you roll if you keep trying harder and harder trails and obstacles.
The bottom line here is that the human body has some pretty crappy design flaws and weak points; the neck and back being a couple of key ones. Even a crappy roll cage or roll bar will probably save serious injury one time... I remember back in the late 60s and early 70s when "roll bars" were being made for the head boards of tubular steel bed frames. Did they work? Sort of because they were better than rolling the rig right onto your head, but that was about it...
Hopefully, this little write up and the pictures, plus the very nicely put together write up link courtesy of The Ranger Station will help you with future plans for a roll bar/cage or point out weaknesses in the current one you have now.
Although this is gone over in the Ranger Station write up, I will briefly cover some strong and weak points of roll bars and cages:
The weak:
Many "factory" cages are only bolted through the sheet metal on the floor board or fender wells of your vehicle. Feel the thickness of the metal anywhere you can: lip of the hood, fender, etc. Picture the contact area provided by four (usually) 3/8" sized bolts with washers. Yeah...makes you think a bit.
Many Jeep style vehicles have no support across the front top of the windshield frame. This isn't limited to Jeeps, but any rig designed along the same lines with an open or removable top. The glass in your front windshield isn't structurally sound. What is left is a pretty cheesy hunk of cheap channel. This doesn't stand up well in a rollover and usually ends up with a flattened front of the hood, flattened windshield...then you finally hit the roll bar. Look at someone sitting in this style rig and draw a line from the front of the hood to the top of the roll bar. Like where people's heads fit in that line?
Another thing seriously lacking in "factory" bars....and even some after market bars, is the lack of any kind of triangular bracing, gussets or cross support. Glue some little sticks together forming a basic box, just how the roll cage is built with no bottom frame. Let the glue dry and push on any corner. What happens? The box collapses. There is nothing to keep is from doing so.
The strong:
Triangulation. Anywhere you can get it. This means on any corner, cross braced behind the driver, cross braced over the driver's head...anywhere. Take that same box you just glued together and glue triangulation anywhere you can. See what happens...
Gussets. Again, anywhere you can get them . Works on the same principle as triangulation, but on a smaller scale and adds an incredible amount of strength.
Plating. By plating, I mean sandwiching the top mounting plate of the roll bar/cage through the cheese metal of the body/floorboard to a heavier piece of steel plate underneath the mounts. This is by no means as strong as a frame tie in, but is a damn sight stronger than the cheese 'bolts through the sheet metal' crap.
Frame tie in. The strongest of the bunch. There are basically three different versions of this:
Where you plate the bottom of the existing roll bar/cage mounts as described above, allowing the cage to be removed at a later date, and do a tubing/plate mount to the frame, either bolted or welded to the frame.
Same as the above, but using bushings where it attaches to the frame to allow for flex.
Welded directly to the frame, either through holes cut in the flooring, tying into the frame, or tying the cage directly to sliders for an external cage.
Crowning the top cage bars or adding a bend. Although for the most part, a straight bar is going to beat the hell out of a bent bar 99 times out of a hundred, there are places where a crowned or bent bar adds strength. This is especially true for the top of a rig. Crowning the bar when it is attached on both ends adds a lot in a roll over, The bar will try to flatten out but has no place to go as it is pushing on both ends. This also gives a "rocker" point if the rig has turtled and needs to be rocked back over onto the wheels. Try tipping a flat caged rig over sometime if you want to see the difference...
A welded cage is stronger than any bolt together cage, but many of the after market bolt together cages, especially for rigs like the Jeep Cherokees are VERY strong. When you figure the welding price of welding an internal cage vs the not too cheap bolt in/bolt together cages, you may find that is the best alternative price wise for these rigs.
Some "factory" cage beef solutions:
Many of the manufactures that make after market roll cages, especially for Jeeps, address most of the known weaknesses in the stock Jeep cage design. Stepping it up a notch, many manufacturers also address the frame point tie in issues with pre made and gusseted frame tie ins. There are also quite a few companies out there that supply additional beef, again primarily for Jeeps, with roll cage add ons like "sport cages"
I happen to be a real big fan of roll bars and cages (Really? I was wondering what the jungle gym junk was on my heap....) especially after rolling a rig frontward and essentially flattening the entire top, leaving me hanging upside down hanging from my seat belt, smelling gas and hearing sparks from under the hood. Yeah, I was by myself, too, and didn't feel much like burning to death, so I was rather inspired to vacate the vehicle though a very (very) small space...Entertaining to say the least. That was the very last rig I ever had that did not have a substantial roll cage, too, and that was many, many vehicles ago. I have rolled other rigs with cages and have been real happy I have had them.
Here is the link to the basic cage design, why, etc. :
Building A Roll Cage For Your Ford Ranger/Bronco II
And here are some pictures for food for thought:
Hope this helps!
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