Standard-Cab Tacoma Rollcage: Design Input

[JESSE_at_TLT]

We're finally gutting our Tacoma (http://www.trailslesstraveled.com/vehicle.php?id=2) to build the rollcage and I thought I'd ask for input in a few key areas before we get too far along.

We put the main hoop (B-pillar) behind/outside the cab when we built our bedcage (http://www.trailslesstraveled.com/viewarticle.php?id=51) because it didn't seem like there would be enough room inside our little standard-cab to put the diagonal cross-bracing behind the seats. That leaves us with a longer unsupported span between the A-pillar and B-pillar than I would like, but I'm hoping we can add enough strength to the cross-bracing in the doors to make up for it.

Take a look at the first image and let me know what you guys think. The main tube that runs along the top of the door down the A-pillar to the frame would be 1.75x.120-wall, but can I get away with 1.5x.120 or .090-wall for the rest of the bracing across the door. Everything will be MIG-welded mild DOM. I'm just trying to keep this standard-cab, 4-cylinder truck as light as possible without compromising safety.
http://trailslesstraveled.com/content/news/rollcage-side-1.jpg

This image is just an interior view of the same thing.
http://trailslesstraveled.com/content/news/rollcage-interior-view-1.jpg

I'm not sure which way would be better to cross-brace the roof (yellow or green). The green would obviously be lighter, but I'm concerned about crushing the A-pillar corners. Yellow seems like the more sensible choice unless I can count on the green tubes to be strong enough in tension to hold everything together. What about material? 1.5x.120-wall?
http://trailslesstraveled.com/content/news/rollcage-overhead-1.jpg

I'm planning on running two bars down the center of the windshield /\ and tying them into the stock crossbar behind the dash. You can see how I've cut through the firewall to tie into the engine cage, but it would be very difficult to run any tubes down to the frame from the dash crossbar (inside the cab) since we're planning on keeping the stock dash and the heater/AC, etc. for now. Will the cross-bracing in the roof help to keep it from getting pushed back/down? 1.5x.120-wall?
http://trailslesstraveled.com/content/news/rollcage-dash-1.jpg

I'm not sure if I'm going to keep the stock inner fenders or not, but I've already clearanced them for 35" tires (http://www.trailslesstraveled.com/viewarticle.php?id=63), so for now I'll just remove what I need to in order to build the engine-cage. The purple tubes in the middle would run right down to the framerails and the purple tubes on the outside would tie into the stock shock-mounts. We're also replacing our 2.5" bypasses (http://www.trailslesstraveled.com/popup.php?/content/techarticles/49/5bypass_shock_installed.jpg) with a new pair of 3.0 bypasses, so there will be some additional tubework back by the firewall. The orange tube would be a bolt-in crossmember. I'm picturing the two main tubes coming out from the firewall and running straight to either side of the radiator, running out through the grill/hood and tying into the bumper. Should I be concerned about transfering the force of a frontal impact through the rest of the chassis? I don't really like the idea of designing parts to give/fail, but I understand why it might be important. 1.5x.120-wall?
http://trailslesstraveled.com/content/news/rollcage-front-1.jpg

How can I improve any of this? I'm open to suggestions. Please let me know if you see anything I should change or something else I should consider. If anyone wants to download copies of the original images to draw on and post with a reply, click here (http://www.trailslesstraveled.com/news.php?id=31).

Thanks in advance.

[elcaprerunner]

I think you would be just fine with a simple X in the roof and no A frame down the middle of the windsheild area. Gusset the A pillars where they meet the roof at the top of the windsheild, and possibly put an X in the rear diagonals that come down from the B hoop, I would think that would be more than enough bracing with what you plan on doing in the doorways. This is the way I plan to do it when I do mine. I am definately no expert, anyone else have a say?

[1450-ranger]

How are you mounting the shoulder part of the 5 points? Looks good otherwise.

[JESSE_at_TLT]

There is already one diagonal brace at the B-pillar and we're planning to X it. I am planning to run a smaller crossbar at shoulder-height from side-to-side where the tubing pierces through the cab. I haven't really thought too much about the seat mounts either. I wanted to finalize the major structural design first.

[Brandon_Charley]

I've never done this, as most people know, but it seems like it is going to be a b**** to get in and out of, especially with the stock dash. Is this something you just put up with in the name of safety?

[Rocker]

As far as the roof bracing goes, I would keep head room in mind. I have talked to some guys who would do your yellow lines so that there is not a tube above your head to be knocking your helmet into, however, I have talked to guys that would do the green lines so that there is a tube over your head for more protection from crushing in. If it were my truck I would do the green provided you are not as tall as yao ming and you can get the seats low enough to not constantly be slamming your helmet into those tubes. It will be plenty strong, don't worry about the a-pillar corners crushing, you have that taken care of with those tubes shooting down from there (in the side view). Connect it to the cab along the a-pillar to brace it even furthur and it will be fine.

Make sure to bend the ends of the roof tubes whatever design you use so that they have to spread the entire cage apart in order to crush in. It will also give you a little bit more head room. Looks like this from the side

____________________
/ \
you know?

[Rocker]

well that didn't really turn out right, move the right slash all the way to the right of the line which represents the tube and you will see what I mean, Im sure you get it. Good luck!

[Josh_K]

You can probably take a step back and go on the light side and be fine. The roof should be fine with either the yellow or the green but I wouldnt do both. The only thing I always see people do that is scary is using a tube smaller than 1.5" x .90" for the inverted V in the center of the window. If that was to brake and come back into the cab, it would be looking to skewer your head.

Josh

[ntsqd]

First rule: No midspan or unsupported loads. That means that you don't have offset tube junctions. All tube centerlines of a given junction intersect each other in the middle of the junction. It also means to not tie a tube to the middle of a span w/o some other tube(s) from some other direction also supporting the middle of the span. Think of stress as being water. Your job is to make it flow thru the cage in as smooth a manner as possible, regardless of how convoluted the path might be.

Top picture:
Where the A post comes down to meet the tude from the engine cage. That bend just above the joint really doesn't want to be there unless you're intending for the cage to fold there as part of the crash energy management plan.
I would be more inclined to bring the tube from the upper corner of the windshield on the A post back to the tube junction just above the door striker, and do a typical X in the door opening. Perhaps make the upper-fwd part of the X removable using Camburg's bolt together couplers if it serves as an occasional DD. If not, then tie the lower windshield corner junction to the striker junction w/ a straight tube.

Second pic:
Upper-outer windshield tube junction needs another gusset tube btwn the windshield cross tube and the cab roof corner tube (extension of the A pillar tube).

Remember that a tube bender is a tool, not an obligation.

[JESSE_at_TLT]

Dalton8Driver-
Thanks for posting. The roof cross-bracing that I drew in yellow and green lines is definitely going to be one OR the other. So you think that bracing the roof like the green lines show would be strong enough to keep the upper/outer A-pillar corners from getting pushed in? Obviously, a big enough crash will destroy anything...



Top picture:
Where the A post comes down to meet the tude from the engine cage. That bend just above the joint really doesn't want to be there unless you're intending for the cage to fold there as part of the crash energy management plan.
ntsqd-
I can eliminate that bend from the A-pillar bar just above the dash crossbar junction. I could probably use a little help planning a 'crash energy management plan' though. What did you think of the engine-cage? Should I be concerned about transfering impacts all the way through the chassis?



I would be more inclined to bring the tube from the upper corner of the windshield on the A post back to the tube junction just above the door striker, and do a typical X in the door opening. Perhaps make the upper-fwd part of the X removable using Camburg's bolt together couplers if it serves as an occasional DD. If not, then tie the lower windshield corner junction to the striker junction w/ a straight tube.
I don't think I understand exactly what you're saying. Could you try to explain that to me again? I'm just trying to strike the best compromise between supporting the outer/forward A-pillar corner (which leems like it needs a second, more vertical tube than just the one running along the windshield), cross-bracing the door area effectively, and also trying to avoid having to enter/exit the truck by climbing through the window. This truck will only be legal to race in 1450 and it does get driven on the street some (mostly to/from off-road trips). I'd prioritize safety above convenience in this vehicle though.



Second pic:
Upper-outer windshield tube junction needs another gusset tube btwn the windshield cross tube and the cab roof corner tube (extension of the A pillar tube).
I didn't draw a gusset in that corner because I didn't know how we were going to cross-brace the roof yet. If we laid the tubes out like the yellow lines, that gusset wouldn't be necessary, right? By the way, what do you think about the roof area?



Remember that a tube bender is a tool, not an obligation.
That's good advise. We're trying to keep the bends to a minimum, but also I'd like the tubing to conform to the body as much as possible. The crossbar across the top of the windshield is a good example of one tube that could either run straight from one side of the truck to the other, or it could follow the lines of the windshied. I understand that a straight tube would be stronger, but it would aslo let the body crush further in towards the rollcage because the tube wouldn't be conforming to those lines anymore.

I should probably mention that this is a 4WD truck and we're installing an Atlas transfer-case in it right now. We're planning to beef-up the front diff/CV's and actually run the truck on some tigher rock-crawling trails. So if/when this thing rolls, it's equally likely that it will be a low-speed flop and if I didn't have to do anything more than re-skin a section of the body, that would be awesome.

[ntsqd]

ntsqd-
I can eliminate that bend from the A-pillar bar just above the dash crossbar junction. I could probably use a little help planning a 'crash energy management plan' though. What did you think of the engine-cage? Should I be concerned about transfering impacts all the way through the chassis?

Crash Energy Managment is also known as "Crumple Zones" Probably best left to Engineers with sophisticated modeling tools. WAGs could get you hurt.

If you're going to pass front bumper loads thru the engine cage to the cab cage, then ideally you neeed to provide a continous, non 'dog-legged' path for those loads clear to the frame at the rear bumper along with diagonals that put some of those loads into the frame along the way.


I don't think I understand exactly what you're saying. Could you try to explain that to me again? I'm just trying to strike the best compromise between supporting the outer/forward A-pillar corner (which leems like it needs a second, more vertical tube than just the one running along the windshield), cross-bracing the door area effectively, and also trying to avoid having to enter/exit the truck by climbing through the window. This truck will only be legal to race in 1450 and it does get driven on the street some (mostly to/from off-road trips). I'd prioritize safety above convenience in this vehicle though.

For a race truck I would bring a tube from the junction of the dash tube and the A pillar tube back to the B pillar tube junction with the tube below the rear window opening. In the door opening below that tube I would install an 'X' of tubes.
That means climbing in thru the window. For a street truck I would still install the X, but would either not install the top tube or would make it removable. I would also consider making the portion of the X coming from the dash tube-A pillar tube junction to the center junction of the X removable.
For the junction of the A pillar tube with the windshield top tube ideally there would be a tube from that junction down and back to the junction of the lower rear window tube - B pillar tube junction. That would be an ingress/egress problem, so some sort of compromise will have to be made.


I didn't draw a gusset in that corner because I didn't know how we were going to cross-brace the roof yet. If we laid the tubes out like the yellow lines, that gusset wouldn't be necessary, right? By the way, what do you think about the roof area?
It would still be needed.
If the green lines clear helmets I think that would be sufficient.