Scratch built trailer - frame material size??? (1 Viewer)

[Lock2Rock]

Hello,

I’m wondering if there is a rule of thumb or chart to help determine the size of material to use for trailer frames. I know the proper way to determine this is through engineering calculations based on the build design, but I doubt most shade-tree builders have this ability.

I need to construct a very stout flat bed trailer to haul a 1,000-gallon water tank. The bed needs to be 54” wide and 12’ long. I’m planning for a 5’ tongue length. In addition to the 500# tank, and 8,000# of water, I’ll have another 500# or so of pump, hose, and equipment. A 2,000# trailer would bring the total weight to 11,000#.

I’m planning to use tandem 6K drop axles with brakes on each axle, but may upgrade to 7K axles. Based on looking at various factory built trailers, I think the minimum frame material would be C6-10.5 (basically 6x2x0.25 channel iron weighing 10.5#/ft). I’m thinking I should use 6x2x0.25 tubing weighing 12.2#/ft. I don’t want to excessively overbuild because it will increase the overall weight, but I don’t want to underbuild for obvious reasons.

Anyone know of a chart or rule of thumb, or anyone have input?

Thanks,
Curtis

 

[REZARF]

Tubing is much stronger than angle, however, your design (chassis) will play a large part in how strong your overall design is. I know there are good plans for sale for trailers, maybe check into one that fits your bill.

Just my.02

Drew

 

[Lock2Rock]

Good point Drew.

I've looked for plans, but have not found a flat bed as small as I want designed for so much weight. As the rear overhang or hitch to axle lengths grow frame material size logically increase. I've looked at some 7x12 12,000# dump bed trailers that used the C6x10.5, but a dump is such a different design (one frame that tilts resting on another that is the real frame).

Thanks,
Curtis

 

[Plowboy]

Just a quick run-through on weight of a box frame and axles comes in about 1200 lbs. Most class 4 trailers are rated at 10,000 and they often use 6 inch channel. Bumping up to a class 5 12,000, I would use the 6 inch box. 12 ft sides, 5 crossmembers and on the tongue extended from the front hanger up to the hitch probably around 8 ft on each side. I pull a 16 class 4 with a bulldozer that weighs 6500. It's made with 6 inch channel and over time it is showing the stress.

 

[Rubiconcruiser]

Use a minimum 4 inch by 1 1/2 rectamgle tube. 3/16 wall

 

[REZARF]

Curtis-

I think you are on the right track, FWIW, www.abctrailerparts.com will make you a custom axle in any load rating and any width for much less than anyone else in the country that I have found. I had a custom built 3500# axle made up for about 150 bucks!

That may free you up to use the material you want and build it the way you desire, I would get on a lot and check out the specs of what the major manufacturers are using, then with those materials in mind, draw up what you need in a trailer and start triangulating everything

Keep us posted.

Rezarf <><

 

[Lock2Rock]

Thanks guys!

Thanks for all the advise guys!

I've checked with www.abctrailerparts.com, and the shipping was not good to California - www.etrailerpart.com appears to be a better choice when I look at shipping.

One question - why, and I know it is common, should I run my tongue all the way back to the spring hangers? I just cannot see the advantage of that design over just bending (cut & weld) the frame rails to become the tongue? FYI, the trailer will already be narrow so I don't think I'll have jackknife problems. Also, due to the narrowness, I'm trying to keep the center of gravity low using drop axles - I'm thinking that tongue rails below the frame will make the tongue very low for my truck hitch, and maybe cause clearance problems.

Thanks again!
Curtis

 

[REZARF]

Curtis-

Simply put triangles equal strength.

When you let the drawbars go all the way back to the spring hangers you get a very solid chassis, where the tortional loads are now distributed directly in the sides of the trailers frame and directly over the axle. It is just a simple way to make a BIG triangle.

You could be fine with a cut and bend, I would just gusset it where you cut it.

Drew

 

[Lock2Rock]

Thanks again Drew! after reading your reply and thinking about it, I understand. I knew there had to be an advantage because I had seen it on many HD trailers.

Cheers,
Curtis