Easy Wooden Bike Trailer

I tried to create a really simple bike trailer for my girlfriend. It turned out to be really sturdy and practicable.

It is designed in a way, that it can be mounted to most bikes, without having to mount a tow coupling first. This is great because all our friends can borrow it and use it with their own bikes. And it still only takes a few seconds to attach it to the bike.

I think this is a great way to reduce car traffic and therefore I want as many people as possible having a such a bike trailer ;-)

I've tried to make all the steps as clear and easy as possible, so that everybody is able to build it. You can customize the size of the trailer and there is an Excel sheet to calculate all the needed dimensions. You only need basic tools and the work can be done in one day.

This tow system only works if you have enough free space on your seat post and it might happen that it rubs off some paint.

Supplies

Tools you need:

• handsaw (or jigsaw)
• cordless screwdriver and drill bits
• rasp
• wood glue

Materials you need:

• wood
• bike wheels (preferably 18 or 20")
• screws

• lashing strap

• (maybe steel plates, depends on the wheels)

Step 1: Getting Materials

Wood

I tried to reduce the amount of different materials used. There are three main materials:

• wooden board, used mainly for base plate
  I used 12mm OSB board, plywood would be the nicer choice
• small laths, used for most of the construction
  I used 23x43mm spruce
• bigger laths, used for the towing bar
  I used 43x43mm spruce

Of course, you can use any size you want, but I think these sizes are pretty good. It's really sturdy, but still not to heavy. You can customize the size of the trailer to your needs and use the Excel sheet to calculate the exact lengths of all the needed parts.

Needed materials for my dimensions (just to give you an idea):

• 0,63 m² board, 12mm
• 12m small laths, 23x43mm
• 1,5m big laths, 43x43mm

In most of the hardware stores in my region, you can buy the wooden boards cut exactly to your needs. This eliminates the need for a circular saw. Then you just have to do the cutting of the laths and some small cuts, which can be done with a hand saw.

Total price for the wood was about €25.

Wheels

I used old 20" bike wheels, which I bought used for €5. You can use 26" wheels (if the trailer is long enough), but smaller would be better, as the center of mass gets closer to the ground.
Wheels of foldable bikes or children bikes work best.

Wood glue

Use waterproof wood glue. The glue is important, without it the trailer wouldn't be sturdy enough.

Lashing strap

The lashing strap is used to fix the tow coupling to the seat post. Any cheap one will do.

Another option is to use a backpack buckle, this is faster and more convenient, but a bit harder to get.

Steel plates

Only needed if you have wheels with quick release.
Look at the "mounting the wheels" step.

Step by step

• find suitable bike wheels
• look up the dimensions of wood laths in your local store (online) and pick dimensions close to mine
• download Excel sheet and put in lath dimensions
• configure ground plane and height to your needs (or leave it as it is)
• print the Excel sheet, you have all the needed info on there
• buy the boards pre-cut to the right sizes
• buy enough laths and screws according to the printout

Step 2: Cutting the Wooden Laths and Boards

Wood laths

Cut the laths to the right sizes according to the file.
This can be done with a handsaw or jigsaw, try to cut it in a right angle.

Cut the edges of part E as seen in the picture.

Wood Boards

The towing bar reinforcement and the wheel bar reinforcements need to be cut in half diagonally. You can then cut away the sharp corners, to make it look cleaner.

The tow coupling needs to be cut accordingly to the picture. You can either do this by drilling the center hole with a big 30mm drill bit and then rasp away the remaining material. Then you can cut the slit with the handsaw.

Or you can also use the jigsaw, if you have one.

If you don't have either of these things, you can also drill a continuous series of holes around the circle. Then cut the slit and break away the material. This is probably the fastest option.

Try to fit the part on your bicycle seat post, it should have some space to move, but not too much.

Step 3: Pre Drilling Everything

Put together the baseplate and the laths according to the picture and mark all the parts on the baseplate with a pencil. That way you can easily find the right spots to pre-drill.

You can do the same with all other parts, put them together like they should be and mark all the locations for the holes. And then drill everything in the end. This saves you a lot of time. The right location for the holes can be seen in the assembly picture.

You should use a drill bit with the same size as the screws, for example 4mm.

You always just drill a hole in the first of two wood parts, which you want to screw together. This way the screw is loose in the first part and can therefore pull together the two parts.

Step 4: Gluing and Screwing

Take the baseplate and lay it flat on the edge of a table, that way you can screw the parts from underneath.

Start with two parts A and the two parts C, one at a time. Apply enough wood glue on the baseplate, where the part is going to be. This is easy, if you have marked the borders with a pencil.
Put on the lath and screw it on from underneath.

Next are the parts D. Apply wood glue on all surfaces they touch (picture), then screw them on from all three sides (or two for the inner ones).

Next, fix the two part of A to the parts D.

Then parts B, F and E.
Make sure every contact point has glue on in and is screwed together tightly.

You can also already fix together the tow coupling, part H and G and the towing bar reinforcements. But don't fix them to the rest of the trailer yet.

Also, the two remaining parts of A should not be fixed yet.

Step 5: Mounting the Wheels

There are two types of wheels, ones with quick release and ones with threaded rods and nuts.

Threaded rod

These are the most common ones for small wheels I think, they are easy to mount. You just have to drill holes in parts F and A and put them in. But the holes should line up pretty good, you can achieve this by placing part A next to part F and drill the hole through both parts at the same time.
The holes should be a tight fit for the axle, otherwise they make a lot of noise while driving. If the holes you drilled are too big, you can put tape around the axle ends, so it gets tighter.
Of course, you can also use steel plates for this wheel type, this will probably make it a bit stronger and more reliable. But I have never had a problem without them.

This only works if the threaded rod is long enough! I would say at least 20mm of free space.

Quick release

For these you have to use two steel plates, which are screwed to parts A and F. Just look for suitable plates in the hardware store, they usually have something that fits. If not you might have to drill new holes, this can normally be done with a cordless screwdriver (if it's not from IKEA :p ). But you have to use drill bits for steel.

Mounting part A

If you have the mounting spots for your wheel, put everything together and screw the "wheel bar reinforcements" on Part A. But don't glue the reinforcements to part A! Otherwise, you can't take out the wheel anymore.
Then glue and screw the assembly to part C.

When mounting part A, make sure that there is no room for the wheel to slide axially, so push part A tightly towards the trailer before screwing in the screws.

The mounting length of the wheel axle can vary, therefore the parts C are calculated too long and need to be cut to the right size now.

In the end you should have your trailer sitting on the two wheels, just the towing bar is missing.

Step 6: Finishing Steps

Mounting the towing bar

Depending on your wheel size and your bike, the height of the towing bar can be adjusted. Put the trailer behind your bike, hold everything together and mark the desired length of part G.
Cut part G to the right size and glue and screw it to the trailer. This has to be connected really good, i used two screws for each connection.

The point where the towing bar is fixed to the upper lath of the trailer gets the most stress. So ideally this should be reinforced. I've used some remaining wood and glued it to the sides, as seen in the picture. But you could also use steel brackets.

Lashing strap

Put the lashing strap through the two holes and close it around the seat post. You can then cut it to the right length.
Another option is to use a backpack buckle, this is faster and more convenient.

Further improvements

• You can use cloth to cover the inside walls of your trailer, that way nothing can fall out. The cloth can easily be fixed with a stapler.
• Put reflective tape on your trailer to make it more visible

Problems with the tow coupling

On some bikes it can happen that the tow coupling slides down the seat post and gets blocked. This especially happens when the seat post diameter is too small for the coupling.
One thing you can do about it, is to make a small wooden disk which can be slid on the seat post like seen in the picture.

Street law

Be aware that the trailer probably isn't street legal in your country. Here in Austria it must have reflective surfaces in the right colors on all sides, two backlights and you have to be able to brake or block the wheels (while standing).
You have to check the restrictions in your country, but i think if you want to, it probably isn't too much work to make it legal.

Final thoughts

If you've built the trailer, I would be happy to see some comments, pictures, thoughts, improvements, … :)
And please let me know if something isn't clear or if there is an error somewhere.

Also, I think it would be cool to write a note on the trailer, so everybody who is interested knows that there are instructions here and that they can easily build it themselves.