Choosing steel for a trailer build

[Haywire]

I'm researching for a potential trailer build that probably won't happen because of the price of steel, but it's fun figuring things out before my bubble gets popped.

It's a 6x12 tandem utility bumper pull. I'm looking at steel, and want to build it plenty stout enough for it's intended purpose, but I don't want to overbuild it. Basically, I will be hauling the little tractor in my sig and firewood. The max I see it getting is 5k in payload if I load it up good with green firewood. For the foreseeable future I'm going to be pulling it with a small V8 and extra steel where it's really not needed just makes it heavier and more expensive.

The tongue... I'm seeing 4" channel with .18" thick web and 1.58" flange width, and a heavier version with a .32" web and 1.72" flange. My gut tells me the heavier version but that's why I'm asking. I tend to overbuild. The tongue length will be about 4' so it will back better and have room for a storage box or cooler. I'm not stuck on channel either. If a heavy angle tongue would suffice, I'm open to that also.

The basic frame... I see commercial MFGs using 2x3x1/4 angle on their economy 7K trailers and 3x5x1/4 on their "heavy duty" 7k trailers. From my understanding, the stiffness/strength of the angle is largely dependent on the vertical member. IE, the 3" side of the 2x3 and the 5" side of the 3x5. Would there be any advantage in using a 3x5x3/16" over a 2x3x1/4? ... Edit: I don't see common availability of 3x5x3/16. Seems everyone lists that starting at 1/4.

Cross members... 24" centers, 2x3x?

Springs.. 1750 is the standard, but I have seen it recommended to use 2400lb. I think the standard is good enough, but what are your opinions?

Ian

 

[sandman2234]

I think the 1750 springs would be enough, but since you know you are going to be loading it to the max of their capacity for your intended purpose, if they aren't too much more money, I would go with the 2400 pound springs.
As far as the costs of steel, since you aren't in a hurry, start looking for it in the used market. You might get lucky, but with today's high scrap prices, that isn't as likely. People are taking notice and less likely to give away/ throw away reusable steel.
As far as the extended length of your trailer tongue, I would reconsider that. If you need room for a toolbox, extend the bed so that the trailer sides continue to give you strength. Extending the tongue is the weakest part because it has no sides to give it strength and the first time you load to max capacity and hit a bump, the strength of that piece of 4 or 5 inch channel is tested. It is just not worth the risk to add the length for that reason when you are building a lightweight but heavy duty trailer. Adding a foot to the trailer length will cost you more, but it will get used more than the tongue and at less risk to the strength of the trailer.
David from jax

 

[bigtiller]

I know it would be a fun project to do, but why bother? Used 16 foot tandem axle trailers are plentiful in any market.

 

[Haywire]

Because I don't want a 16x7 or 8 trailer. I want a 12x6.

Ian

 

[ohbuckhunter]

Steel prices very from day to day. You being in Central KY I dont know how far Louisville , KY cause we have a branch out there ALRO STEEL. I know our branch Columbus Ohio sell scrap steel ( full sheets 4x8, 4x10, 5x10, 6x10) at a lower price cause there not traciable. Lost heat number or something of the nature.

 

[jeffsw6]

From my understanding, the stiffness/strength of the angle is largely dependent on the vertical member.

The webbing transfers load across a truss, and the metal between the webbing is really just holding it together. The third side is what keeps it from twisting and bending as you drive down the road.

If you imagine a ladder long-ways laying on the ground with a load sitting on it, obviously the rungs are what would bear the load, and the legs just hold the rungs in place. A truss works the same way but the "legs" are angled to transfer load to the ends of the truss.

 

[Haywire]

So... does that mean the thinner but taller 5x3 angle is better or no? LOL. I did a google search for a chart or calculator that would compare angle strength, but didn't find one.

Ian

 

[LD1]

So... does that mean the thinner but taller 5x3 angle is better or no? LOL. I did a google search for a chart or calculator that would compare angle strength, but didn't find one.

Ian

Let me give a little background on channel iron first so you understand what I am talking about and then I'll give you a good link.

Channel iron (like I-beam) gets the majority of its strength from the flanges...NOT the web.

So...pound for pound, more steel in the flanges in relation to the web is a stronger use of the weight.

Next, the way channel iron is labled. For example, a C3x5 means

C=channel
3=depth in inches
5=weight per foot

so your two 4" channels you were looking at are probabally C4x5.4 and C4x7.5

The C4x7.5 is about 39% heavier, but only 19% stronger in the xx plane (vertically)

Now for how to understand the following link. You need to look at the moment of inertia of the channels. These on the chart are the Ixx and Iyy colum. The Ixx is how strong it is vertically, and the Iyy is how strong it is laterally (horizontally). And these #'s are linear. Meaning that 4 is exactally 2 times stronger than a 2.

Structural Steel Channel Section Properties Moment of Inertia, Steel Beam Size,Cross Section Area - Engineers Edge

Notice that a C5x6.7 is about 60% stronger than the heavier 4" you were looking at in the xx direction, and a tad bit stronger in the YY direction as well. BUT, since it weighs a little less, it is probabally cheaper since steels "root" pricing is usually by the pound.

But without knowing exact dimensions, the C4x5.4 is probabally pleanty strong enough. But if you want peice of mind, the C5x6.7 would be my choice over the heavier 4":thumbsup:

 

[Diamondpilot]

I know very little about steel other than how to stick a few pieces together with my stick or mig welders. I do know trailers though and have been in the business for about 20 years.

Back in 2004 I wanted to get rid of my 25+5 25,000# GN and build a 18' low boy car hauler.

Long story short by the time I bought wheels, axles, tires, brakes, and steel it was more than the cost of a new trailer. This surprised me but I had not even included the tongue jack, coupler, wiring, boards for the floor, or paint. My time was also not factored so there is no way I can build a trailer for what you can buy one for.

Unless you have half of it laying around or are getting it free just by new.

Chris

 

[Haywire]

I see.. the C5 will be stronger than the heavy C4 but be lighter at the same time. I looked at their angle chart.. they didn't have that spec in the unequal leg chart, but did on the equal leg, so I compared 3x3x3/8 to 4x4x1/4... The 3x3 is 1.76 and the 4x4 is 3.04. It's significantly stronger. That was a lot of help LD, thanks.

Ian