Serious trailer design questions

Ig, I prefer ball couplers. The reason being that if it starts swaying and I hit the brakes, I can be assured the trailer is going to take the decelleration smoothly.

Brakes: It depends on how much weight you are carrying on it. Heavily loaded trailers can generate tons of inertial force. putting that force into the tongue when stopping. I prefer electric brakes and a modulator as they allow me to "preload" the trailer brakes so it decellerates first.

Axle capacity: With a 3500 lb axle, you have less than 2700 lbs of weight capacity. The bed itself and the frame add in to it. So, if you are planning on carrying heavy equipment, raw materials or dirt, you're going to make a few trips.

Low trailers are difficult to see when backing. Keep in mind that a low floor helps keep the center of gravity low. That's a good thing. If you are hooking up to a tall truck, you need to account for hitch height when building the tongue. Simply stacking blocks on the end of the tongue to achieve the height may be easy, but not necessarily the best solution. You want to direct towing forces into the frame of the trailer and the towing vehicle for controllability. So, you need to gradually build up to the hitch height at an angle. Just vertically stacking blocks underslings the towing forces on the coupler and converts it to vertical force through the connection axis.

Framing. Frames are always a compromise between weight and strength. The weight of the frame reduces the hauling capacity of the unit. Moreover, the weight generates towing forces in all kinds of directions. 1/16 material might be okay if you crossbrace and put gussets in the corners. Look at a race car chassis' for ideas.

Hitch point. I think the optimum angle for the tongue triangle (assuming you are going with a boom tongue which I think would be a bad idea) is about 58 degrees. If you go to Northern Tool, they have coupler plates made to surround the tongue members and put them at this angle.

Good Luck.

OK, I agree.

Here, I am not sure if I would ever need to carry more -- how would I unload something that weighs, say, 2 tons? I also can make a couple of trips if I need ot bring two tons of dirt, that should happen exceedingly rarely.

Remember that the bed has solid sides, so it is still going to be visible even if it sits relatively low.

Yes, that's definitely a good point. I will try to make sure that the frame is at least approximately aligned with the ball height.

One point to note here is that the bed already has ribs for crosswise strength (ribs go crosswise under the flat bed surface). See

Here, I do not understand you, are you suggesting to use triangular A frame, or a single member boom frame? (you said that it is a bad idea)

i

Use springs intended for trailer use. Car/truck springs, even if rated for the load, are too soft and deflect excessively. 3500 lb and

4500 lb trailer spring sets are $44.99 at Northern Tool. Consider using a drop axle, or (if you're really confident in your welding) making a drop axle or modifying a found axle. I modified a drop axle. I don't have much road clearance, but it has never bottomed other than scraping the hump off of a dirt trail and the low bed is very convenient. 1/16" thick sounds far too thin to me. I used 3/16" wall rectangular tubing throughout my trailer and for the tongue. (Tongue is square, but squares are also rectangles, right?)

Advantages of lunette/pintle hitches are that they are easier to align for hookup (as you say) and more tolerant of uneven terrain. Disadvantage is that they bang a lot when hitting bumps. I regard them as better for off-road but not as good for highway. Beware of cheezy ball hitches, though, there are some crummy ones on the market. Another possible advantage to a lunette/pintle hitch is less risk of some idiot borrowing your trailer and hitching it to the wrong size ball.

Ball unless you plan to tow it off road. The pintle hook / lunette is used primarily on trailers towed over rough terrain due to it's greater freedom of movement. They clang and shock the heck out of your drive train otherwise.

1,000# generally, at least legally in most states. I've done a whole lot higher on a couple occasions (very carefully) personally when the appropriate adapters for the wiring were not available, but I wouldn't recommend it.

If you just believe your truck has it, it doesn't. No GM vehicle I'm aware of comes with a brake controller. The tow package gets you the correct wiring harness, but you still have to add a controller. The Tekonsha Prodigy is a nice one.

Electric brakes are really about the only way to go. Surge brakes are a pain and mostly good for rental construction equipment trailers.

Personally I'd go for a tandem axle configuration with 3,500# axles. Your trailer box will be an overkill waste of dead weight unless you put enough axle capacity beneath it to carry what the box can carry. Tandem axle is recommended since it will make your tongue weights more controllable since your pickup will only handle 500# tongue weight without a weight distributing hitch.

Look at the axle selection available from Northern Tool or Tractor Supply. If you have a store nearby, both have them in stock.

Torsion axles will give you the lowest ride height since they don't require additional leaf springs. A "drop" axle mounted over leaf springs will be next in line. You said you got a book on trailer fab, suggest reading it for trailer suspension options.

Bad design. Read your trailer book. 2x4 on it's side won't be anywhere near strong enough in the direction that needs it. Please go to a trailer place and look at a trailer of similar capacity. Take a tape measure and note pad. Do it right so you don't kill someone.

Portions do, others are miles off.

Pete C.

I drive an F350. Low trailers drive me nuts. If you see the sides, you aren't straight! Even so, there is a wide angle the trailer can be at and you not know it. I almost always try to keep the tailgate down so I can see. Fifth wheels spoiled me.

I'm a bit confused. The initial picture you cited showed it on a forklift. If this is still the underside, those ribs should be okay as long as your frame is tied in well. Gussets!!!!!

Sorry about the confusion. I hate, Hate, HATE boom tongues. They are simpler to build, but act like a torsion spring. Hit a bump and the forces are going to twist it. I much prefer the triangle. Another point to consider is you can make a boom tongue too short. The triangle form tends to force you into an easier to drive length.

They will clunk on ever takeoff and stop emoty, but settle right down when loaded. My dad has a lifelong distrust of ball couplers, but I've not had a problem with them so far. The biggest advantage of the lunette is fewer people will want to borrow it (and then mess up the taillight wiring, mangle the license plate, get 2 flats, and drop it off in the middle of the night).

Check the webpage of your local DOT. Mine says over 3000 requires brakes. Some say 2000. Some say depends on tow vehicle capacity. Laws trump physics as far as limits go--know what yours are.

If you've already got the controller then that's definitiely the way to go.

Drop axles, especially with mounting the axle on top of the springs instead of under them, or torsion axles with the arm "clocked" to give you some drop. Champion trailers

goes into a lot of the options and is very informative in general.

1/16 is about 16ga. My little HF trailer is 11ga, and it flexes. I think you'd be happier going quite a bit thicker. Most landscape trailers are something like 1/4" angle. --Glenn Lyford

Agreed on that, though it should not be a problem with this trailer bed.

The picture at nf6x shows underside of another trailer. They are all similar. See all pictures of his trailer at

Oh, I see. Yes, that makes perfect sense to me.

i

I see. I kind of like the idea of people borrowing my trailer, though.

Good point. I have pretty much decided to install brakes.

Seems like I was wrong, but I will buy one.

Thanks, I opened that site and will read about it.

I like these two torsion axles:

(30 and 10 degree)

I think that using such an axle would allow me to have some framing underneath and to get a true 5k GVWR trailer.

Sorry, I meant 3/16". I apologize.

i

Yes... I would not lend it to idiots, but if I lend it to someone, I would give them my pintle hitch.

i

In most states you must have trailer brakes and a breakaway package (including a battery on the trailer) that applies the brakes if the trailer parts company with the tow vehicle for a gross trailer weight of

1000 lbs or more. You'll probably hit that before you put so much as a feather _in_ the thing. You had better check with your local motor vehicle office to see what the requirements for Illinois are, so that you can build it to suit them the first time, as it probably needs to pass an inspection in order to get registered.

As for the other question you _should_ be asking, check your owner's manual for the GCTW - gross combined trailer (or towing, I forget) weight, which tells you what the absolute maximum combination of gross vehicle weight and gross trailer weight is safe for your model of truck, engine, transmission, etc.

It may have the wiring, it still needs an electric brake controller, and verification of the wiring and controller working. Electric brakes are by far the most sensible option, and you need brakes.

I have decided to definitely get brakes.

Makes sense.

My wheel well is for single axle only. I will probably use a single axle, either 3,500 lbs, or 6k lbs. I have not yet decided.

Hm. They have a store 2 hours from me. Only 1 hour from the military base. (same direction). Interesting. I will check around.

I will read that book again tonight.

OK... I will read on it... Though they suggest something similar here:

note that crosswise pieces I already have, underneath the bed.

OK... Obviously I need to be humble and read up a lot... I have two weeks to pick it up...

Thanks Pete...

i

Without a doubt, I will get brakes.

My truck is rated for towing 9,200 lbs (which I do not really believe).

OK... that's been decided...

thank you...

i

You MOST DEFINITELY want heavier than 1/16" wall tubing, and you want

2X4 tubing in the UPRIGHT, NOT FLAT orientation. Tie the A-Frame of the hitch to the longitudinal members and gusset the corners well. Fasten the longitudinal members to EVERY CROSSBAR SOLIDLY. You want a heavier axle than 3500 lbs or you WILL be overloading it. Doesn't take many 200 lb parts to make a ton. And you DEFINITELY want electric trailer brakes. Your Chevy MAY have come from the factory with a brake controller, but if not, get a good DIGITAL controller. Tekonsha is good, so is Reece.

Northern Tool in particular has a big selection of trailer parts in stock. Basically everything but the bulk steel. Tractor supply has a bit smaller selection, but still enough to do the job.

Not the same. Look closely at where the spring hangers are on that little trailer. They are using 2x3 angle for the main frame rails, 3" direction vertical and most importantly it is not a single 2x3 angle making the frame, it is a truss structure.

Your frame rails are going to end up inboard of the sides of the box and they need to have adequate structure by themselves. Look at the pic you linked of the underside of the trailer, that big ladder frame of what looks like 4" or larger channel is what is required to for the trailer.

Read all you can, and look at other trailers of comparable capacity. Others have engineered these things, copy their designs.

Pete C.

I'd use 2 2X4X3/16" minimum longitudinals on each side, with the springs between them. On edge as previously stated.

It was a typo. Sorry. I meant 3/16.

OK... thanks...

i

Having people borrow your home built trailer is probably assuming a lot of liability you don't want. Loaning out your commercially built trailer would put most of that liability on the manufacturer.

Pete C.

That would be with either a weight distributing receiver hitch, or with a 5th wheel or gooseneck hitch. Otherwise you're at 500/5000 max with bumper or receiver hitch.

Pete C.