Info on steel for trailers

[fields_mj]

I had a post recently asking some info about rebuilding a trailer. After getting a lot of good feedback, I did some more searching and finally came to the conclusion that I will eventually have 2 trailers. One for the ATV, and one for the truck. I had a few people recommend that I use square tubing instead of channel. I took a good look at 2" tubing, and found that even the heavy wall tubing was weaker than the thinnest 3" structural C Channel. So, I thought it might be helpful to others to post some of the information that I looked up. This information is in regards to weight/ft, strength (Mass moment of Inertia), and a rough price reference. So here goes.

Description Wt/ft MMI Price per 20'
2x2x3/16 angle 2.4 0.27 $45
2x2x1/4 angle 3.2 0.35 $50

2x2x3/16 tubing 4.6 0.749 $100
2x2x1/4 tubing 5.9 0.9011 $120

2x3x3/16 angle 4.1 1.09 $55

3" #4.1 Channel 4.1 1.66 $70

4" #5.4 Channel 5.4 3.85 $95
4" #7.25 Channel 7.25 4.59 $130

4" #7.7 I beam 7.7 6.08 ???

5" #6.7 Channel 6.7 7.49 $120


The prices were roughly what I found at some on-line sites and they are comparable to what I can get the steel for at some of the local welding shops.

Based on this, I decided to modify my existing trailer using 3" channel so that it can haul my ATV and I can pull it through the woods behind the ATV. For a trailer to haul a cord of wood behind the truck, I'll probably get some pricing on some 4" I Beam, and then use 3" channel for the cross members.

Hope this helps someone.
Mark

 

[cjcocn]

Thanks for posting that up.

I will be building a couple of trailers and the steel specs will come in handy.

Rep sent!

 

[Beefie]

A C- channel trailer will last way longer than a trailer built out of tubing. The air inside a tube can cause it to rot from the inside out, you won't even no its happpening until its too late. My neighbor has a 5'X8' C-channel trailer , all he ever had to do was replace the wood on it. I have a 5'X8' also ,It is a tube built trailer and it is showing signs of weaking in the tube area, so Now I can't load it as much till I fix it or sell it.

Just my 2 cents worth.

Beefie

 

[dancan]

Get your tubes sprayed with any fluid type undercoat (not used oil) , keep the dirt out of them and they'll last , a little more work than c channel .

 

[fields_mj]

Get your tubes sprayed with any fluid type undercoat (not used oil) , keep the dirt out of them and they'll last , a little more work than c channel .

One of the reasons that I posted this info was because I wanted to show just how poor steel tubing is when used to build a trailer. I was surprised at how weak it was compaired to its weight and price. Pound for pound, 2x2x3/16 is about the same weight as 3" channel (I'm being generous here), and 2x2x1/4 is about the same weight as 4" channel (again, generious). 3" Channel has twice the strenght of 2x2x3/16 tube, and yet it costs 30% less. 3" channel is about 50% stronger than 2x2x1/4 tube, and it's significantly lighter, and it's only about 60% of the cost. When you look at 4" channel, there's just no comparison.

My point here is that unless a person has a free supply of square or rectangular tubing, there's just no reason to ever use it. Even if a person does already have the tubing, they need to realize that it's just not nearly as strong as they might think.

I'm not trying to flame anyone here. I was just surprised by the information. I knew that the channel would be better, I just never expected it to be so much better. I honestly figured 2x2x1/4 would be about as strong as the light 3" channel. Looking at the numbers, to me its not really in the same ball park. Then, when you look at the cost, wow, a real eye opener for me.

 

[KD57]

Good for you, going with the 2 trailer plan !!

 

[tomtrees58]

look at a used one some times its cheaper got this one last week

 

[fields_mj]

Yup, that's the plan. I wish I was in a position where I needed the bigger trailer now instead of the smaller one. Found a travel trailer that has been stripped down to its frame for $300. Just not what I need right now, but I'll probably look for something like that when the time comes. Can't buy the steel for a good trailer for $300, let alone tandom axles, springs, breaks, and such.

Mark

 

[Captain Crunch]

One of the reasons that I posted this info was because I wanted to show just how poor steel tubing is when used to build a trailer. I was surprised at how weak it was compaired to its weight and price. Pound for pound, 2x2x3/16 is about the same weight as 3" channel (I'm being generous here), and 2x2x1/4 is about the same weight as 4" channel (again, generious). 3" Channel has twice the strenght of 2x2x3/16 tube, and yet it costs 30% less. 3" channel is about 50% stronger than 2x2x1/4 tube, and it's significantly lighter, and it's only about 60% of the cost. When you look at 4" channel, there's just no comparison.

Comparing 2x2 tubing with a 3" channel is comparing apples to oranges. The formula for section modulus for rectangular sections is 1/12*B*H^3 - 1/12*b*h^3 (B, H are outside dims, b, h are inside dims). So the height of the section is cubed, meaning that the height of a structural member is very important. Similar for C channel, but the formula is more complex.

To give an example in the other direction, a 4 x 2 x 12 ga tube has a MMI of 2.6 (60% greater than the 1.66 for the 3" 4.1 C channel) and weighs a similar 4.3 lb/ft.

You are on the right track, however I disagree that tubing is a poor choice due to strenght/weight when selected correctly.

All that and I still agree that C is a good shape due to corrosion, repainting and repair ease.

 

[fields_mj]

[COLOR="royalblue
Comparing 2x2 tubing with a 3" channel is comparing apples to oranges.

Not really. It's more comparing dollars to dollars, strength to strenght, and weight to weight. You've given some very good engieering information, and it's accurate. What I'm refering to is the application of that information. The derivation used to derive the MMA of a shape is no longer relavent once the MMA has been determined. I can dig out my old Mech of Materials book if I'm interested in formulas. What is relavent is the strenght of the profile vs it's weight and cost.

The only reason that I say that steel tubing is a poor choise is because there are noticably stronger profiles available that are lighter weight for significantly less $$. Unless the tubing is avialable for free (which could be the case for some), using steel tubing to build the trailer would cause a person to spend more money than needed and result in a trailer that was heavier AND weaker than what could have been built for noticably less. In 15 years of engineering work, I've yet to come across a mathmatical formula, buisness case, or anything else that could make the steel tubing look good for this application. Believe me, I've been in situations where I've had to try....

 

[Captain Crunch]

Unless the tubing is avialable for free (which could be the case for some), using steel tubing to build the trailer would cause a person to spend more money than needed and result in a trailer that was heavier AND weaker than what could have been built for noticably less.

In our two examples using 3" C and 4x2x12ga tube, the trailer would be approximately the same weight, approximately 50% stronger and, your right, the steel COULD cost 40% more. For a 5x 8 utility I deigned the total length of steel, be it C or tube, was 41feet so the cost premium would be a whopping $46! LED light upgrades and chrome wheels cost more than that. Double that 41 feet for a "real" sized trailer and the premium is still not that bad, given the increase in modulus.

I still maintain that 2x2 x 3/16 tubing is a bad choice for this application, low height, very thick walls do indeed yield a terrible strength to weight ratio.

 

[fields_mj]

In our two examples using 3" C and 4x2x12ga tube, the trailer would be approximately the same weight, approximately 50% stronger and, your right, the steel COULD cost 40% more. For a 5x 8 utility I deigned the total length of steel, be it C or tube, was 41feet so the cost premium would be a whopping $46! LED light upgrades and chrome wheels cost more than that. Double that 41 feet for a "real" sized trailer and the premium is still not that bad, given the increase in modulus.

I still maintain that 2x2 x 3/16 tubing is a bad choice for this application, low height, very thick walls do indeed yield a terrible strength to weight ratio.

True. I think most of it could be chocked up to perspective. Realistically, on a small trailer, $40 would be about 20% of your steel budget depending on the design. But it's still $40. In my house $40 is a nothing to sneeze at. It may not buy much these days, but it will buy 2 boxes of generic #3 diapers and a happy meal to share with the kids...

 

[Bob Wright]

Get your tubes sprayed with any fluid type undercoat (not used oil) , keep the dirt out of them and they'll last , a little more work than c channel .

Actually its moisture from condesate that is caused when the sun heats up the metal. Take a clean dry plastic pop bottle and screw on the lid and lay it in the sun for a few days and see what gathers in it. Tubing should have drain holes in it for sure as well as something sprayed as Dan said. Here is a link to some of the 500 trailers i have made over the years Trailers i have built pictures by aametalmaster - Photobucket
...Bob

 

[Captain Crunch]

It may not buy much these days, but it will buy 2 boxes of generic #3 diapers and a happy meal to share with the kids...

I'm down with that, at our house it's new cloths for the rapidly growing pre-teen boys!

 

[Beefie]

This is a good thread with a lot of really good info init. We all like to get the most out of are dollar. I like the c-channel because you can paint all the sides. Here in Wisconsin they like to salt the roads in the winter, and if salt can get into something and sit, well you no the rest.


Beefie

 

[gwiley]

check steel distributor not welding shop

Your prices look high compared to what I am paying. I recommend that you dig further to find the steel distributor and see if you can buy direct from them. The welding shop has to add to the distributor price to pay for handling the steel.

Comparing prices in my area yields differences that are sometimes DOUBLE the lowest price at the distributor.

Also bear in mind that steel prices tend to move with the commodity markets and most places are now adding fuel surcharges (yet another reason to go direct to the distributor).

 

[fields_mj]

Your prices look high compared to what I am paying. I recommend that you dig further to find the steel distributor and see if you can buy direct from them. The welding shop has to add to the distributor price to pay for handling the steel.

Comparing prices in my area yields differences that are sometimes DOUBLE the lowest price at the distributor.

Also bear in mind that steel prices tend to move with the commodity markets and most places are now adding fuel surcharges (yet another reason to go direct to the distributor).

I can get it for less. Those were just averages for reference. If I drive 25 miles into the nearest "town" I can get it for a pretty good price. If I drive 3 miles down the road to the local weld shop, I pay 15%~20% more, BUT I save an hour of my time. Plus, if I'm buying 20' sticks, the local shop is close enough that I can stick it in the truck bed and take the back road home and not have to deal with any cut charges, or any traffic. So it's a trade off. Plus, the place that's further away is open from 8 to 5, M-F and it's in the wrong direction from my work which makes it difficult for me to get in there to pick up the steel. I can also order through work if I'm willing to wait a while until another delivery is coming this way. Then I'm dealing directly with a distributor, so the prices are great, and since I have my own shop here at the office, I don't pay any cut charges here either