Difference Between Rectangular Tube Sizes For Frame Build

How thick are two short planks? What wall thickness will you use?
Gussets and other engineering design details matter too.

But in general, 3x6 is monstrous big, I'd say.

 

I think building whole frame with 1/8 X 2 X 4 tubing would be just fine

 

I'd go with 3/16, not so much for beam strength, but for more meat at welds and stress points.

 

1/8 is plenty in reality. 3/16 x 2 x 4 is going to give you plenty of strength for anything you want to do. Original Jeeps just used 1/8" c channel, not even rectangular tube

 

Agreed. But steel quality today is dubious, and in my neck of the woods anything ⅛" or less can rapidly corrode dangerously.

 

We have rust in bodies out here but never have to worry about rust in frames. Our DOT has recently discovered that salt melts ice however so it will probably be in our futures also.

 

Depends on the span of the main rails............If there long .188 wall may be a better choice and then use .125 wall up and over the suspension at each end..................also depending on your welding type & experience be it , arc, mig or tig and the thickness of the brackets , roll bar Etc a heavier wall tubing like .188 wall may be easier to attach things too especially if the brackets are 3/16" to 1/4" material. Much easier to weld like thickness's together when using conventional welders than welding thick to thin............

 

2x4 .120 wall vs .188 wall = about 2 lbs per foot additional weight...........

 

I went with 2x5x.250 wall. My CJ6 without me in it, aluminum body and no cage yet is over 4100 lbs now. I think 2x4x.188 is more than enough.

 

4100........pounds? Not kg right? Curb weight of a 6 from the factory was like 2400 wasn't it. Not hassling ya. Just surprised by that much of an increase.

I think the 2x4 material would be sufficient but, it may easier to use the 2x5 as it's closer to the factory height. Just thinking of the suspension brackets and the way the body mounts will fit up. I'd probably opt for the thicker .188 just for a little reassurance, though the .120 would likely suffice.

 

Dan says the rig weighs about 2500 lbs.............Just for comparison a length of 2x4x.120 wall tubing attached between 2 points 10 ft apart could easily carry 1500 lbs dead center with about 5/16" of deflection which is well within its stress range..........the same scenario using 2x4x.188 wall tubing to get the same 5/16" deflection would require 2350 lbs to be placed dead center...........so obviously just a change of .060 in wall thickness makes a huge difference in it's ability to carry extra weight.

Going back to the Obvious the car would probably have at least 45%+/- of its weight distributed over the front axle and 55%+/- over the rear axle , leaving some unknown transfer of weight between the two points at COG at any given moment. But that weight at COG between the axles if measurable is likely to be less than 500 lbs.

As you can see 2x4 in either .120 or .188 would do the job............2x3 tubing under the right conditions would also be fine in a car that only weighed 2500 lbs..................2x5 tubing in my opinion would be an overkill.............I would probably stay with the .188 wall just for the ease of attaching parts.................but again I'm not building it.

 

I originally bought 2x4x.125 for my frame but will be getting 2x4x.188 before it's built.

Those dimensions do seem quite overkill for a vehicle of its size

 

Yeah, it's 4100 lbs....portly! I have extra crossmembers, reinforcements and gussets galore, 17, yes 17 body mounts, Dana 44s a winch, tire carrier and full size spare, sm465, 2x5x3/16 bumpers, etc..etc... it all adds up. I thought it'd weigh in at like 3500 when I was done. Boy was I wrong!

 

3/16 wall is easier to weld. Less warpage. Much more forgiving. I have no idea how the frame is built on a rover, so there that. Mine is working very well with 2x4x3/16 wall