rectangle tube, or dom?

[RangerSVT]

So I'm in the planning stages of SVT's next phase. I'm building a new suspension, and along with that a new foundation to build off of, a new frame. My current weight is about 7k, with the new axles I'm expecting at least 8k. I'm looking to lose a few pounds with the new frame. My choices are 2x4x3/16 rectangle tubing, or 1.75x.120 dom, double tube frame. Dom is about 2.1 lbs per foot, rectangle tubing is about 6.8 lbs per foot. In the end, I'm looking at about 4.5 lbs per foot for the dom, and 6.8 lbs for rectangle. My question is, do you think the dom will be strong enough to support the rig? Axles are about 1300 lbs each, plus rims & tires, engine power will start as 400hp, but will increase as high as 1,000hp in the future. What say you?

SVT

 

[alwaysFlOoReD]

Out of my line of expertise. But, a search of OFN Forums would probably give you the info, or at least a nod in the right direction.

http://www.offroadfabnet.com/forums/index.php?

Richard

 

[Bray D]

This is a tough question. I'll answer your question with some more questions, haha.

Do you plan to keep it a cab truck or are you building a full tube chassis? 8k is a seriously heavy rig, and 1000hp isn't something to take lightly either. The round tube can absolutely be used, but the strength will have to come from the overall design rather than the strength of the material.

Speaking of the material itself, why are you locked into 2x4x3/16? Are there any other wall thickness options?

That are the strengths of the materials your considering? The specific material type would get us started anyways, e.g. A500 rectangle or 1020 cold rolled round, etc.

 

[RangerSVT]

Im not locked to that rectangle size, could go 2x5, or 1/4", etc. Also would do 2"x.120 dom if it'd be better. Keeping the cab, skinning the bed sides, cage (haven't decided internal or exocage, but leaning towards exo with cab tie-ins). For the (dom) frame, i was thinking double tube, with either "H" or "/ \" bridges. Not locked to anything, want to build this once, and with experience guiding me. More background, motor will be all aluminum 4 valve 4.6, trans 4R100, tcase 1356/205 (custom all steel reduction box) or NWF box, axletech 4000 axles (where most of the weight will come, 1,300 lbs each) triangulated 4 links front and rear, 49" iroks. Power will probably be about 750 realistically, but has the capability to go all the way to 1500. I don't intend to run it past 1,000, but could run it up to that 4 digit mark. The lighter i get it, the less power i will need. Based on what i have now weight wise (stock frame 96 x cab ranger, 91 kp hp front 60, 98 60U rear, 5.0, 4R70W, 205, 47" michelin XML's, right at/over 7k), I'll pick up another 1k or so in weight. I'd love to be sitting at 6k, in which power would be 750 max.
Back to the frame, I'm not familiar enough to know the capacities of each tube. So, school me

SVT

 

[bobbywalter]

your solidly in tube frame territory with a shit ton of triangulation via nodes to keep weight down and strength maximized.


just cursory looks at the goatbuilt type chassis and bigfoot combinations would line it up fairly plain and simple in my eyes.

 

[bobbywalter]

i am assuming your using a big block of some sort.

 

[RangerSVT]

Nope, all aluminum 4 valve 4.6, the teksid/intech motor...

SVT

 

[Bray D]

Not much info here, but at least there's some discussion:

http://www.pirate4x4.com/forum/general-4x4-discussion/1571345-frame-design-square-tube-vs-round.html

If we're only considering the frame rails, I would lean towards rectangle tubing. It's going to resist bending in both directions better than a truss style tubular rail. Of course you could make the tube structure more rigid in one direction by increasing the distance between your tubes, but you'll never make up for the lack of strength in the other direction simply because it's geometry is limited to the OD of the tube.

There's absolutely some high HP rigs with tube frames, but it's supported by the remainder of the tube structure. They're full tube chassis. Tying an exo into the frame rails (rectangle or round) will add rigidity, but your design is limited due to the spatial constraints of the cab.

If you're keeping the cab, I would lean towards rectangle frame rails. You can strengthen it with the exo and supporting crossmembers just like you would a tubular frame rail, but you'll be starting with a stronger base to build from.

If you lose the cab and do a full tube chassis, I would use round tube frame rails. Your strength would then be provided by the remainder of the tube work, and you'd save a bit of weight in the end.

I'm pretty sure structural rectangle tubing is A500. That will give you ~46ksi yield for a grade B material.

http://www.onealsteel.com/carbon-steel-hollow-tube-a500.html

Does anyone know the mechanics of the DOM that we use?

Once we have the mechanics, we can study the different geometries to see what would be best in different loading scenarios.

edit: Looks like a 1020 DOM from this supplier will get you 55ksi yield. Slightly stronger material than the rectangle, but I'm thinking the geometry of the rectangle will benefit you more than this slight increase in strength. I'll have to run the numbers later when I get a chance.

http://www.onealsteel.com/carbon-steel-dom-tube-a513-type5.html

 

[RangerSVT]

Thats kind of what i was thinking, but let me throw this in there. Behind the cab will be all tube, with tabs to mount bedsides to, very similar to what Kyle has done. I plan to tie the exo to the cab in several spots, strengthening both the cab and the exo, almost the same way you tie an internal cage to the frame through the body. Would running slugs "through" the body (again, similar to internal cage tieing into frame) for lateral bracing, reinforcing the dom frame chassis be better than a similar setup using the rectangle tube, or would switching to an internal cage be more beneficial? I understand running the numbers in both cases (which is the purpose for this thread, i don't know the numbers) is needed, but would the design of being able to do an internal cage reduce the spatial constraints that hinder a dom frame?

SVT

 

[Bray D]

Is it safe to say that the remainder of the tube work will be the same regardless if you use a truss style round tube main rail or a rectangle main rail?

If so, that'll allow us to simplify the analysis substantially. Maybe we should start there, anyways.

 

[bobbywalter]

in my case rectangle hydroformed rails tied up with a combination of rockers and limited exo with custom bed like i currently use makes sense.


ideally i would just skin a cage structure and gaurd it to resemble my favorite rbv, but i am far too lazy for that.

primary there is street vehicle and i would just be increasing the strength factor, i can not wheel my truck like i used too because i am past the chassis limits due to weight, tire size. final hp and tq numbers will likely not exceed 300hp/550 ft in street driving.


just on axle weight and tire size a custom ladder chassis based on all around goals makes the most sense to me. there is a custom build at pirate of similar scope with a sport trac body running a idi diesel with a hd custom rectangle frame as a base, and it is the easiest way to go for speed. but will have inherent packaging limitations and weight/ride heights in places you may not want it.

figuring out all of the component layouts for the powertrain/cooling/creature comfort layouts could yield a light frame design with the best range of suspension and ride height ranges. a linked air bag suspension would really maximize the beast. lay it right down for egress/ingress and ride like your favorite couch through the rocks and laugh off abuse handily.


so i really wonder about the main use of the build....if your going straight mud racing i can see the engine choice as it will stand out and kick ass.

though a 1000 or even 700 hp intech i can not see as long lived in this sort of application if low speed trail work will be a regular thing on the menu of activities.. i assume it would be a 2nd gen romeo with the forged crank but thats allot of sauce for such a load with small displacement. i would think a turbo or two on a v10 would be ideal.

the alum italian block 4.6 would be insane fun on a sand rail or mustang...sleeper crown vic. monster truck that does trail work i am not so sure there is a happy zone for it.

have you seen 69diesel lovers build on the pirate?

 

[RangerSVT]

Is it safe to say that the remainder of the tube work will be the same regardless if you use a truss style round tube main rail or a rectangle main rail?

If so, that'll allow us to simplify the analysis substantially. Maybe we should start there, anyways.

Correct. Still gonna have the internal/exo cage, and tube bed, as well as engine cage, no matter the main frame material. Frame crossmembers will also exist (thinking 4 total, not counting cage tie ins).
Basically, it will have the cab, motor, trans, tcase(s), axles, front fenders, hood, lights, grille (if possible) and rear bed skins. However the frame and cage need to be designed to be strong, yet light (without going chromoly dom) weight, I'm all for it. The different tube i mentioned is just what i had in mind from the knowledge i had. If something else would work better, I'm open to suggestions...

SVT

 

[RangerSVT]

Bobby, i seen the sport trac build, as well as a few others. Funny you should mention an airbag suspension, as thats the setup im going with. 8" travel bags on a 2 to 1 cantelever suspension (maybe 2.5 to 1, will see what i need when i start building). Crawling and moderate rockbouncing are the intended use for this build, not so much mudracing, but could if i get a wild hair.
Engine wise gonna stroke the italian block to a 5.0 for more torque useage, and strap the M122 i have to it, and pulley according to needs. From there i can write a tune to fine tune the power where i need it. In my area, i can get away with driving it on the road locally between trails, even with the wide width, hence the reason for keeping the cab and not going full tube buggy...

SVT

 

[Toreadorranger]

If your going to be running a full cage and tube bed, you don't need to go so thick on the rectangular tubing. The strength of the frame is going to be combined with the cage and tube bed, you would be adding extra weight with the .188 or .25" wall tubing. I'm building a similar setup rig, but with a buggy chassis instead of the frame and cab setup. (it will be skinned as a ranger)

My chassis uses 2x3 .125" wall tubing as the main rails, by the time you fish plate the rail joints and run necessary cage and bracing it will be very strong. If you need thicker in areas for mounting the motor or suspension, just plate it in those sections. Will help keep the weight down, and strength where you need it.

I'm running 47's as well, with rocks and approx 450hp LQ4 V8, will be for similar usage as yours as well. The chassis was made by Bent Fabrications.

 

[RangerSVT]

I'm thinking I'm leaning more towards full dom tube frame. Which lead me to thinking about doing a lighter double tube frame for a trailer. I think too much...

SVT