C channel vs square tubing

[iconicflux]

I've noted that most popup trailers use C channel for the majority of the trailer parts and I wasn't really sure why that was but I think I've finally started coming across why that is.

It seems that the c-channel has a much higher resistance to bending for a uniform load with forces applied downwards.

There's some interesting talk about this at: https://www.arboristsite.com/community/ ... rs.167226/

So I started checking out what they're saying and it seems like it's true that C channel has a much higher moment of inertia.

Couple that with corrosion resistance and repairability and now it totally makes sense why companies make trailers out of c-channel.

So I started figuring out my trailer with C-channel and it turns out that it saves weight AND is stronger.

Sooo fascinating.

It does seem though that because of torsional flex it's probably not a great idea to put axles onto c-channel unless it is reinforced to stop it.

[RJ Howell]

I get 'I' beams vs. Sq or C, but C vs. sq... Just don't see the additional strength without many other factors involved. Now, C vs. Sq with preventing any corrosion allows for surface area to be treated. Then comes how to prevent even that with sq....

I build with Sq'ed.. Just me and willing to be convinced otherwise.

[tony.latham]

...but I think I've finally started coming across why that is.

Me too. They use it for the same reason they use OSB.

Tony

[iconicflux]

LOL yeah that's probably true too. It IS cheaper and if you're having to deal with warranty stuff then it makes sense you'd use what costs you less.

...but I think I've finally started coming across why that is.

Me too. They use it for the same reason they use OSB.

Tony

[Ottsville]

Properly sized C channel and angle iron would be fine for pretty much all of the trailers that people are building on this site. We are talking about trailers that are under 2000lb loaded.

The debate over C versus tube has been hashed out on any site that talks about trailer builds.

[MickinOz]

Not convinced c - channel is stronger than box section with the same amount of steel in it.

https://www.youtube.com/watch?v=8Ob2tVP5miE

[PCO6]

Round tube would be stronger than square tube or C-channel but generally speaking a pain in the butt to build a trailer with.

[Pmullen503]

The rigidity of the tear drop itself has to be considered when thinking about the frame. That said, I wouldn't use C-channel for the tongue.

The use has to be considered too. I would want a rigid frame for off road use to reduce the wracking forces on the trailer body itself. SUV's meant for road use are unibody, off-roaders pick something with a real frame for the same reason.

[PCO6]

The rigidity of the tear drop itself has to be considered when thinking about the frame. That said, I wouldn't use C-channel for the tongue.

The use has to be considered too. I would want a rigid frame for off road use to reduce the wracking forces on the trailer body itself. SUV's meant for road use are unibody, off-roaders pick something with a real frame for the same reason.

This is generally true (unibody vs. frame) but unibodies can be stiffened for off road use. It's a common thing to do on a Jeep Cherokee XJ for example.

[Sparksalot]

For a given thickness and material, the square will be stronger. Not significantly so. In practical use, very likely you’re looking at 1/4” channel versus a 1/8” tube.

I like the idea of square or rectangular members, but you have to consider how attachments are made. With a c channel, it’s easy to just drill holes and bolt on. With the tube, it’s better to weld on attachment points and bolt to those, in order to not crush the tube.

A benefit of tube is the ability to conceal stuff like wiring in it. As noted above, it also conceal corrosion if not completely sealed.

[MickinOz]

What I don't get: hot dipped galvanised steel is as common as a common thing over here.
Why not build with it if you are worried about corrosion?

[saltydawg]

What I don't get: hot dipped galvanised steel is as common as a common thing over here.
Why not build with it if you are worried about corrosion?

It can be done, but as an individual building one frame its not worth it. I can build a 5x8 or 10 frame with less than 300 bucks in steel. Getting it galvanized can cost over 1k more.

Then lets be honest, even a raw steel frame will last 10 years if not exposed to salt. How many teardrops last that long. A teardrop might see a few thousand miles a year, but the box is exposed all year, and leaks happen.

[QueticoBill]

Just for bending strength, a channel will be stronger than a square tube that weighs the same per foot. Consider a C3 x 4.1 is a 3" channel weighing 4.1 plf and has a moment of inertia - the property that determines bending in the X axis - of 1.66. A TS 2x2x3/16 weighs more at 4.32 plf but has a moment of inertia of 0.64 - less than half.

My opinion is there are advantages and disadvantages of each that are far more important to consider than just the bending strength per pound of steel, especially for the relatively short spans in tiny trailers.

On galvanized, I believe nasty to weld and you still have to protect the welded area, but I'm old and there may be newer ways to solve that than were available when I learned welding - in 1969-1970.

[QueticoBill]

Want to avoid rust and finishing? Stainless steel obviously. Just follow Space-X's lead.

[twisted lines]

Cutting SQ is easy with almost any saw.
Coping Channel is not so much


A Light Channel may be great flat under the floor, cross members, or dropped floor.
Holding a water tank