Roll cage question

Im a noob.

Im also dumb.

what I want to do is probably pointless.

That all being said, I am looking at roll cage ideas for a truck, and seeing that it has a full frame, the cage needs to be mounted to the frame, but this will result in some places being more narrow than id like.

In addition, there is a lot of room between the frame and the ground, more than I can handle by lowering the vehicle.

The question is, can I run square tube across the bottom of the frame and then use those as a mounting point for the cage?

This would eliminate the narrow spots id like to avoid, provide a flat mounting surface for a belly pan, effectively lower the truck and put the roll cage on the outside of the passenger compartment like you see on off road trucks.

You could.

I would make some outriggers that are as tall as the frame instead though. Anything you can do to spread the load over a larger area or weld will be better. Maybe an added on outrigger and the square piece combined.

Do you have any rule set you have to deal with?

In reply to jgrewe :

Not sure what you mean by outriggers.

I intend to run it at the challenge, the local drag strip and some auto crosses

In reply to jgrewe :

Thank you! Outriggers is exactly what I'm thinking of, now that I know the term to look up.

So one way or another, outriggers will likely be used, the question remains if I can run them across the bottom of the frame to reduce the amount of air space under the truck and to box in all the turbulence causing lumpy things down there.

I imagine structurally it could work but you're adding a lot of weight and expense in steel. I'd close the bottom with an airdam and side skirts from cheaper plastic sheet. 

Keep in mind... roll cages are not required unless you run faster than 10 seconds or 135 mph.  In the 25 years of the Challenge, there are VERY few cars that have gone that fast.

I question the idea of running crossmembers under the existing frame. Adds weight, reduces ground clearance. Most importantly remember the purpose of a roll cage is to resist the forces during an extreme event, including vehicle rollover. If the vehicle is upside down then all the force is hanging on the connections between the truck frame and your crossmembers.  There are lots of guidelines for making strong mounting plates for this reason. If your mounting points are under the frame, you defeat the entire goal.
 

Might be hard to get through tech with such an unconventional design.

What I'd do first is find an off the shelf kit and see what they do. What truck? 

I'm this video they go through and cage their ranger with a prefab kit, it should give you some ideas. 

In reply to SV reX :

It's an AWD Bravada.

I am aiming for reduced ground clearance as well as a way to get things that currently hang below the frame up into a belly pan.

It will likely never get into speeds fast enough to require a cage at the track, but my research says that if it looks like a cage, it has to pass tech as a cage if it needs it or not.

I appreciate all the insights from you guys. I will have to consider carefully before making a plan

What do the rules say you need as a cage?  That is way more important than what some guy on the Internet has for an opinion.  

If you aren't going fast enough for a cage, I wouldn't run one.  And the idea of mounting a cage to the frame instead of the body scares me.  You are attached to the body, not the frame.  What if a wreck bad enough to need a cage pulled the body off of the frame?  Since the harness is going to attach to the cage and the seat is attached to the body, now you are the Play-Doh in a squeeze-out-silly-shapes set.

Outrigger 

In reply to ThePoors :

Yes. If it looks like a cage, it should be properly built as a cage. My suggestion was to eliminate the cage. 

If your concern is the $2000 Challenge, then your rules are the NHRA.  Your local drag strip will be the same.  You don't need a cage according to the NHRA. 
 

Running the crossmembers under the frame is unconventional. It's gonna have a hard time with NHRA tech. 

In reply to Pete. (l33t FS) :

I dig it - but if you crash hard enough a cage would've helped a bad cage is "likely" worse than no cage, but no cage in a body on frame vehicle when a good cage would've mattered ... well ... obviously that could also be worse. 

Judging by the questions asked and this response:
"I intend to run it at the challenge, the local drag strip and some auto crosses"

I'd suspect no cage is a good thing for OP until they understand what they want out of their build, etc. I'd go to your local events, observe and ask questions. For autoX for the most part a cage isn't really necessary, and of course depending on your speed drag racing is a fairly safe event for most cars until it's not.

For a more direct answer to your questions, this thread also contains a caged-track "car" Toyota Tacoma, you might PM the OP there and get some pictures/answers. 

https://grassrootsmotorsports.com/forum/grm/track-day-driving-education-what-next-advice/272007/page2/
 

Not to stir the pot, however, I believe the "suggestion to understand what the OP wants out of the build" is a very valid suggestion.

YRMV
 

In reply to RacingComputers :

What I want out of the build is to drive around in the woods and at the dunes, and maybe the beginner-style mud pits or rock piles with big tires, the torsion bars cranked up, and a nice exo cage in case I tip over.

Then, the next day, swap tires, crank the torsion keys down, throw in a two-inch drop block (I mean, I'd prefer to have airbags, but that's not likely in the cards), and go to the local ice race or autocross.

On the third day, I hit up the local drag strip and dont get kicked out because the ex0-cage that keeps me safe in the other activities looks too much like a roll cage and does not meet tech.

Maybe I'm over thinking, as I doubt I will do any mud pit or rock climbing events, but I may encounter them in my off road Gambler 500 style wanderings, but protection would make me feel better and a stiffer chassis would be helpful in any of the situations mentioned.

Now, I already know that this build wont be very good at any of this, but I should be able to have fun doing it.

Vehicles with a full frame are supposed to have the cage attached at the frame, only unibodies are allowed to be attached to the body, but in the case of an exo cage, the cage goes around the body.

I ran into something kinda sorta the same.  It was a VW beetle that the guy wanted to go drag racing in.  First thing I did was read the NHRA rule book on cages.  Man that's a different animal than SCCA cages and frankly their way of thinking safety kind of sucks. 1 5/8" tubing was speced for every car no matter what the weight was, and they allowed ERW pipe.   I added extra bars; diagonals in main hoop to make it safe in my mind. I ended up removing the heater boxes and running 2" square stock as a perimeter on the pan.  The cage mounted to the 2" and had plates that carried on to the pan.  I also added vertical plates to bolt the body back on to the pan.  I did this in my garage and had the body hung from the ceiling.  Using pulleys and ropes, I could lift and lower the body for test fitments.  Once the main cage was done, the front and rear suspension beams, or whatever the VW guys call them, were tied into the cage as well.  Came out really slick, and from what I was told, the guy that teched the cage was seriously impressed.  My one and only drag racing cage, although I have done several muscle car roll bars that are similar in main hoop design.

The problem I've seen with exo cages is there is no way to put diagonals in places to stiffen up the structure. They look cool but I think the effectiveness as a cage sucks for the weight you add.

In reply to ThePoors :

What exactly do you think 'reduced ground clearance' in and of itself is going to gain you, both on and off road?

In reply to Driven5 :

less air under it,  boxed in lumpy parts that currently sit slightly lower than the frame and a nice flat surface. Clearly, it won't help off-road.

jgrewe said:

The problem I've seen with exo cages is there is no way to put diagonals in places to stiffen up the structure. They look cool but I think the effectiveness as a cage sucks for the weight you add.

They also don't really help much for stuff you need a cage for, since the tubes by definition can only be loaded in bending, not tension, and bending is exactly what tubes are weak in.

I can see an exocage getting bent in such a way that you can't open a door, too.

You've all made some great points.

I may have to just rock a roll bar and call it good

In reply to ThePoors :

I love the idea of an exocage.  Because I like the aesthetic.  In a Mad Max kinda way.

It's hard to make it also enhance performance or safety. 

SV reX said:

 
Might be hard to get through tech 

Shirley, you jest!

ThePoors said:

In reply to Driven5 :

less air under it,  boxed in lumpy parts that currently sit slightly lower than the frame and a nice flat surface. Clearly, it won't help off-road.

I'd argue it won't really help much on-road either. But if you still really want the 'aero' improvement, even though it'll be a lot of time and effort for little gain, I'd consider building a completely removable dropped under tray and air dam instead.

In reply to SV reX :

I would prefer to remove the entire body and have nothing but cage, but I like windshields and roofs!

In reply to SV reX :

I would prefer to remove the entire body and have nothing but cage, but I like windshields and roofs!

I am cutting the rear passenger compartment off, so the roll bar portion of the cage, if I build one, will be triangulated