Cyclaholic

Here's a few of rules of thumb I've developed through experimentation over the years that work for me....

1. Look at the point where the trailer hitches to the bike, and the points at which the trailer's wheels touch the ground. They form a triangle, right? OK, you want to keep the sides of the triangle reasonably close to being the same length. If the side of the triangle that lies along the trailer's axle line is the base then I would keep the height of the triangle (i.e. the distance from the trailer axle line to the hitch) to a maximum of about 1.5 to 2 times the base.

2. You want the center of gravity of the trailer (especially when loaded) to fall pretty much on the axle line of the trailer wheels so that there's very little upwards or downwards force at the hitch. that means that you want the wheels pretty close to the middle of the trailer, not all the way back down the end.

3. You want to make the trailer as low and as wide as reasonably possible so as to keep the center of gravity (when loaded) as low as possible, the lower it is the more laterally stable it is. I try to stay below 3:1 width to height ratio.

The one big variable here is just how much stability do you want? I often take sweeping bends at up to 20mph with 50lb on the trailer on less than perfect surfaces and I can hardly tell its there. I occasionally even take a short cut home from the grocery store down a stretch of singletrack. That requires a nice stable design and a good hitch with no slop. You may be perfectly happy with something less than that.

donnamb 

Please post your trailer construction tips in this thread. It would be nice if we could make them as "generic" as possible so they can be applicable to many types of projects. Tips for rehabbing trailers are welcome, too.

Nightshade

A really decent homebuit trailer that can be 100% recycled free materials

https://www.motherearthnews.com/DIY/1...e-Trailer.aspx

StephenH

I was just down at the local "Northern Tool and Supply" store, and noticed they have bicycle-style wheels that could be used for bike trailers. These are 26"x2.125", 20"x2.125" and several smaller sizes. Wheels have big hubs, heavy spokes, bearings already in place to take maybe a 5/8" or 3/4" axle. I haven't used those, so can't vouch for durability or capacity, but they could be just the thing for some trailer applications. They also sell some lawn carts using similar wheels. And a bunch of go-cart type wheels and tires for that matter.

StephenH

A brainstorm struck. Somewhere on here, I was reading that the extra weight of a trailer was a problem going downhill, as your breaks weren't any better. Meanwhile, I was just at a city auction a couple of weeks ago, where one of the bicycles auctioned was this little BMX-type bike with a working disc brake on the front. So...get that front fork, build it into a trailer, and you have trailer brakes!

JeanCoutu

If you want to build a tongue so that it won't break, here's what you do: Visualise this part at least twice as strong as it needs to be... Now double it & add some metal bits to help resist twisting, and it's just about right.

https://i181.photobucket.com/albums/x...n/cae00b09.jpg
https://i181.photobucket.com/albums/x...n/9857a76f.jpg

HandsomeRyan

Are 12" wheels, salvaged from a childrens bicycle, too small for a light duty cargo trailer? It would be used on pavement only. The attachment to the bike would be a center mounted gooseneck piece so there is no conflict of the pulling arm being too low for the rear axel.

astronomerroyal

12 1/2 " wheels are fine. This is what I used. Sadly I haven't found 14" rims, which would be ideal. However, 12 1/2" wheels have all sorts of benefits, like lowering the centre of mass, are lightweight etc..

ThatHertz

I was thinking about building a single wheeled "BOB-style" trailer. Does anyone know if it is necessary to have a tongue that mounts to both side of the rear axle when using this (single wheeled) type of trailer? It seems to be the norm in photo's but is it necessary?

Also this looks like a good bank of ideas for anyone who considering building a single wheeled trailer.
https://www.singlewheel.com/

Cyclaholic

Ye's, you need a torsionally rigid connection between the trailer and the bike, otherwise the trailer will just fall over.

I'm working on a single wheel trailer now. It's my first single wheel design so I'm using this prototype to test a few ideas, and just to gain some experience on the dynamics. I started by looking at the best elements of the "BOB Yak", the "Third Wheel", and a number of other commercial designs. I then added several of my own ideas and designed it around materials and manufacturing techniques I have at hand.

My concept is a tubular steel chassis that has enough flex at the design weight to act as suspension. That's to alleviate the shock stress on the bike at the hitching point, since it carries about half the weight of the trailer & cargo. The same chassis can use a 700c or 26" wheel. The cargo area is a modular design that will allow it to be easily changed between a hard plastic box with lid, a hammock style net with a couple of duffel bags, or any other specialised module for a specific task such as an animal cage or padded box for sensitive/fragile equipment. There's also a couple of other design elements that you'll just have to wait to see

The hitch is basically the chainstays from two dumpster frames, you can see the donor frames in the first picture. The connecting points are tie rod ends. You can see how they connect to the trailer chassis in the pictures, the connection to the bike frame isn't built yet.

The trailer with a hammock cargo net and the road wheel you see in the photos should come in at around 10 pounds, with a 20 gallon hard plastic cargo box it may reach 14 pounds. It will have a cargo capacity of 70 pounds and could potentially be built lighter without compromising strength..... and it cost almost nothing to build!

Cyclaholic

Those trailers are designed with a rigid mount and a swivelling tail wheel. When cornering, the center of mass of the trailer is describing a circle of greater radius to the circle described by the center of mass of the towing vehichle, but it is travelling at the same linear speed as the tow vehichle. this means that the center of mass of the trailer is travelling at a higher speed, and generating a greater centrifugal force than the tow vehichle. That has the potential to completely wipe you out!.... Ever seen those cop shows where the cop uses his front bumper to tap the side of the bad guy's rear bumper causing the bad guy to spin out and lose control? well, it's essentially the same effect - your rear end is getting pushed out of the corner.

Wino Ryder

Here is a few pics of my trailer hitch arrangement I made for my new trailer. It is very simple and cheap if you are looking for something in a seatpost attachment. The rubber fuel line acts a shock absorber sleeve, and it eliminates any slack or bumping when stopping and starting, slowing down or turning. The hitch pin (bolt) slides thru the fuel line, which is pushed into the eye-bolt and inserted into the bracket. It allows for full articulation and seems to work great so far. I used a 5/16 bolt with the threads ground off, then drilled a small 3/32 hole at the top for a keeper pin. The piece of fuel line I used had to be drilled through so the 5/16 bolt would easily slip through it.

As for the bracket, its an old driving light mount, pirated from my sons Dodge Powerwagon, clamped to the seatpost with a simple hose clamp. The white pvc pieces is from a pvc pipe cut in half, lengthwise, and serves as a sleeve to protect the seatpost. The inside diameter of the split pvc pipe is close to the 27.2 mm size of the seatpost. I opted for this arrangement because there is no way in hell I'm going to rig up a hitch post on my Columbus SL frame.

Cheap and very effective.

JeanCoutu

It's occurred to me that I found a good way to test a trailer's weak points when I built it up. What I did is I showed it off to the teens at the park near my place, and let them play with it and generally give it a good beating, until something broke. Then I fixed/beefed it up and let them have at it again, and the process got repeated. But after that nothing more broke on it. I figure this is better then having it break down when far away and actually hauling stuff.

StephenH

"Those trailers are designed with a rigid mount and a swivelling tail wheel...That has the potential to completely wipe you out!..."

Note that this is concerning single-wheel auto trailers, which were configured completely differently from single-wheel bicycle trailers. On the auto trailers, the trailer can't swivel relative to the car, but the wheel on the trailer swivels relative to the trailer. On a Bob-type trailer, the trailer would turn on a shorter radius just as described for a normal auto or truck trailer.

gerv 

After reading this article, I was just curious about how the author made the dropouts for the wheels out of plywood.

My solution would be to use a 36 inch piece of 2 by 2 aluminum angle.... cut the things into 4 sections and bolt it to the trailer.

However, just curious about this design. Seems a little iffy to me. Any thoughts?

astronomerroyal

I haven't tried this ^ design, and it looks good, but I think his desire for dropouts compromises slightly the overall merit of that part of the trailer.

On my second trailer I used short pieces of aluminium angle to support the *inside* end of the axle, and instead of drop-outs I just drilled holes. He seems to be doing it the other way round. His inside drop-out is cut into the frame(?) and the outside one is cut in a small tab of plywood. Using the yard stick to makes sure everything is in line across the trailer is a good bit of advice though. I assume plywood doesn't split, but that would be my fear for those small dropout tabs. A little bit of metal wouldn't go astray there. Not sure what the rules are for remaining '100% free and recycled materials', (which doesn't seem to be his claim).

I suppose I would've also put some sort of brace or diagonal cross-beam on that hitch arm. Looks as though there'd be a concentration of (leverage) stress at the hitch-trailer link, whenever the trailer goes over a curb etc.

Nevertheless, I certainly take my hat off to the gentleman.

gerv 

This article features one of the easiest designs I've seen yet for a trailer. It resembles the design I conjured up from the Mother Earth news article mentioned above, using wood instead of conduit for the frame.

The article also features a pretty easy hitch design. Not sure if anyone would care to comment.

gerv 

Here's my trailer project. I used 2 by 2s and a piece of 1/2 inch plywood that was lying around the garage. At the moment I don't have anything leading to the bicycle, but that shouldn't take too long.




For the dropouts I used a piece of steel angle I found at Lowe's. $9. I hack-sawed it into 4 pieces. Then I sawed a channel so that the wheel could slide in and out.

JeanCoutu

Electric box covers with extra bits of metal, screws & stuff.

gerv 

That looks sturdier than my design and plate covers are about $.50 cents each. If my angle steel is to flexible, I might add some extra plate like you did. I'm guess that would let me add much more weight.

I am working on the trailer hitch this weekend (unless the weather is good and I can go for a bike ride...). I'll let you know how it goes.

Raiyn

You mean like this?

Rehabbed a Kiddie Trailer

donnamb 

Exactly.

bloompedal08

After this unsuccessful (yet instructive) experiment, I thought I'd share my experiences of "How not to build a trailer"....this is the "Model A"



Basically, a very unstable trailer. The wheels were steel-rimmed 27's with road tires. This placed the chassis pretty high, and with the "tuff box" strapped to it, made speeds greater than 15 mph rather precarious indeed...

Here is a closeup of the hitch and yolk assembly (sorry about the poor quality, but I had a bad experience with this setup so I didn't take a lot of snapshots):



I modified an axiom pannier-type rear rack with two plates (on both sides of the pannier tubes) to accept the yolk, which was bolted to the plates. The yolk had a female heim joint which bolted through the yolk, allowing swivelling. The heim joint was pinned to the aluminum tongue of the trailer. Aluminum tongues are bad, with this type of hitch. Not enough strength to take on the "up and down" movement caused by hills and sharp vertical angles (ie: the numerous hills of south-central Indiana, train track elevations, etc...) Later models were modified with steel tongues, which work great.

The long and short of it is that too much vibration was transmitted through the pannier tubes, creating a REALLY unstable riding experience. I suspect that the height of the tongue attachment was also a factor, tho I can't be sure. All I know is that at speeds of 20 mph, the thing would invariably create an insurmountable death wobble that caused the trailer to flip over. Fortunately, because of the independent swivel of the joint/tongue, this caused no adverse effects on the bike/rider. However, it did wound my pride a bit.

Moral of the story: Keep it low.

/edit: and don't attach your trailer to flimsy aluminum pannier tubes.

xddorox

I get more emails about that article than any other. I always wonder how many trailers were brought to life since posting it. The ones I built are still alive and well.

Gerry

cerewa

The bottom of your plastic container is above axles that are 13 1/2 inches above the ground. I went for 4 inches instead.

I built my trailer with a frame almost the same shape aside from the tongue part. The space between the wheels on mine is empty, though, and I bolted my large plastic container between the outer frame rails so that the axles of the wheels are well above the bottom of the container. I used 20" wheels, so the axles are 10 inches above ground.

This is much better setup from a center-of-gravity standpoint.

Using smaller wheels also allows you to put the wheels further back, which reduces the "death wobble" tendency. In my opinion putting the wheels toward the rear is a good choice if your hitch and trailer tongue are strong enough to carry substantial weight. It has no negative effect on the bike handling, and under hard braking your rear wheel will be better able to maintain traction, avoid jackknifing, and provide braking force at the same time. (but still, brake with front and rear brakes, not just rear!)