Trailer frame design

kaiser715

kaiser715

Doing hard time
Joined
Jun 1, 2006
Location
7, Pocket, NC
So....I brought this home today:

20170808_141527-L.jpg



I'm going to build a trailer frame for it (I've built 6 or so various trailers before, and haven't killed puppies and nuns yet, so don't go there).

Bed is 9'8" long, and 91" wide. Set up for a frame about 44-46" wide. Planning to run duals, maybe a gutted FF dually rear. Will do about a 30" x 90" platform across the front for a genset and fuel tank, and an A-frame tongue. That would make frame rails about 11'4", plus the tongue.

What would y'all use for the frame rails?? I'm thinking 5" or 6" channel. What weight?? Probably the same stuff for cross members.

I do have some 4x6 rectangular tube, either 120 or 3/16's....figure 120 would be too light. Otherwise, don't know about rust and holding moisture, mud, etc if I use tube.

Ideas??

Thanks,
 
There's no reason to use the same channel, etc., for the crossmembers that you use for the rails. You're just adding a lot of weight because the crossmembers are shorter and don't need anywhere close to the stiffness of the main rails.

My intuition says that using 4x6 rect tube for 11 foot rails is probably very heavy overkill. It's hard to beat channel for ease-of-use and bending stiffness for the weight, even though I like the torsional stiffness of rect tubing more. If I was going to use rect tube, I'd be thinking more of 2x6 instead of 4x6 because the long dimension is really the important part for bending loads.

I'd do some deflection calculations with the sections you're thinking of using (there are online calculators) to see what bending stiffness, etc., is going to be.

I'm sure you've already thought of this, but doing some math on the total weight of box, genset, fuel, tools, etc., and then comparing to a cargo trailer of a roughly equiv rating is a good sanity check for main rail sizing.
 
Why not use a truck frame? Pinch the rails up front for the hitch. Already has springs. Cut the center out of the differential. Maybe hydraulic brakes?
 
5 inch main rail. 3 inch or 2 inch channel side to side. That body should already have support rails in it. Yours will only add square rigidity. When you mate the two it will be plenty strong. I dislike tube on any trailer due to corrosion.

Channel works for many manufacturers like Hudson Brothers.....

I got some clear steady burn scene lights that should fit those big square warning reds on the back of you want some rear facing clears for work lights.
 
Took the tape measure to the body tonight.... From the mounting bolts, it looks like the frame it was mounted on was 33" wide center to center. Frame tunnel is almost 48" wide. Body only hit frame at 4 points, 2 front, 2 rear.

Body is 93-1/4 inside between the wheel wells. Measured my neighbor's 2002 F350 dually, looks like outside tire width just shy of 94"...inside of fenders about 95". Maybe I'd be OK with stock size duals, as long as the travel is such that the top of the wheel does not go above the wheel opening, or might make contact. A little too close as it is.

Got a buddy with a leftover Dexter 10k trailer axle (went from triple to tandem), if I can get it here from TX cheap. Set up for duals, electric brake, 74" wms, 44 or 46" spring centers (I forget which he said).

Unsure what total load will be....tried to make an educated guess based on square feet of panels, guessing most 16ga, some is heavier. Still seems to weigh a lot more than I guessed (like when I tried to lever up one end with a rock bar to get blocking underneath it and the bar was flexing instead of lifting). Felt like a lot of weight on the flatbed trailer headed home. I wouldn't be surprised if it's 2500# or better. Lighter than the CJ, but definitely felt it back there. Trailer frame and running gear will add several hundred more pounds. Then whatever goes in it. Wouldn't be surprised to easily hit 5k+ total weight.
 
My former Department had a similar Equipment body on a 1992 Superduty. But we had a 250 gallon water tank in the middle, along with a Diesel powered pump & diesel generator. No compartment on the back, as that was the pump panel & hose discharges. Custom built fire department body. It was Overbuilt, as Fire trucks are, with double wall doors, & heavy gauge steel. Their Much heavier & stouter than the Standard Service body!
 
Sounds like you need a cab-chassis rear axle, instead of one from a dually pickup. They are typically a little narrower.


Sent from my iPhone using Tapatalk
 
tw89yj said:
Sounds like you need a cab-chassis rear axle, instead of one from a dually pickup. They are typically a little narrower.


Sent from my iPhone using Tapatalk
Click to expand...
This exactly, we built plenty on just cab and chassis. If someone wanted a dually width from a used pickup or such all the width changed. The mount you described are typical. Usually a hitch was welded to the rear of the bed at step bumper. Depending on the body guys it was then welded, bolted, or both at the frame.
 
I would find a cheap truck axle to use. Could gut it, or set it up to run something off the pinion while in tow. Think of an alternator or pump of some type to charge batteries or some other task while in tow.

If you didn't want duals, you could easily repurpose a less desirable axle. Depending on what all you are planning to put on this trailer and use it for, a std half ton axle would likely be plenty.
 
Back
Top