Versatile "carry-a-bike" Cargo Bike Trailer

If you are anything like me, you not only like cycling but have elected the bike as your favorite means of transportation. You like practical solutions that allow you to use your bike as often as possible, overcoming challenges of cargo transportation that would normally require the use of a larger motorized vehicle. But if you are anything like me, you either don't own a car or want to minimize its use. Then cargo bikes and cargo bike trailers are the way to go to move around your larger/heavier items. And, if you are anything like me (by now it should be clear we have something in common) you not only want to use your bike to carry the weekly groceries, your musical gear to go basking across town or the supplies from your umpteenth visit to the local DIY store - you want to be able to carry another bike!

If this sounds interesting you are very much like me - in fact we are twins separated at birth: we know about the n+1 rule, we adopt abandoned bikes, we search "bikes" on gumtree/craigslist for no specific purpose, we can ghost ride another bike (though slightly dangerous and often illegal) but we sometimes need to transport a bike unable to roll on its wheels (or a frame without wheels for that matter).

In this instructable I will show how to convert a child carrier bike trailer into a versatile "carry-a-bike" cargo trailer that can be used to transport traditional cargo objects as well as an adult bike (but it really works with any bike size)

Potential carry-a-bike scenarios (that will no longer require a car):

Collect a newly purchased bike
Take a bike to the shop
Collect an abandoned bike off the street
Take a bike to a bikeless friend/partner and go for a ride together
Return a bike left at your place
Deliver a restored/serviced bike
Use bike x to collect bike y that you wisely left out of the pub after n pints
Take TWO bikes for a ride (ok, this is getting silly)
...

If you like this instructable please vote in the Bicycle contest and Move It contest (button on the top right of the page). Thank you!

Step 1: Tools and Materials

Materials:

Child carrier trailer (I found mine on Gumtree for 30$)
Metal mesh (I found one and bought the other)
Metal threaded rod
Cable tiers
Bolts
Washers
Rubber rings (I was looking for plastic washers then came across these in the plumbing section of the local DIY shop)

NOTE: please disregard the T shaped chrome tubing.

Tools:

Drill and drill bit
Cutter
Wrench
Hacksaw
Pliers

Step 2: Strip Down the Trailer

Remove the fabric using a cutter. I was too excited about my new trailer I forgot to take pictures before stripping down the trailer. I recommend Tater Zoid's excellent instructablefor an overview of this step.

Save the red reflectors for later use.

Step 3: Cargo Box I: Floor

Once you are left with the backbone of the trailer the next step is to build a cargo box. I suppose there are several ways to do this but I opted for a cage kind of look, as I thought it would be lightweight and ideal to use bungee cords. I was lucky to find across the street a grill-like alloy frame of a portable closet that was about the right size and sturdy enough to create the trailer's floor. I shaped the frame with an hacksaw, cutting off the excess length and removing the cylinders at the corner, so that it would fit nicely on the trailer. I then used cable tiers to secure the floor to the trailer. After a few rides I was happy with the overall performance of the trailer but frustrated at the rattling noise of all the metal parts bumping against each other (especially when travelling without any cargo). I removed the floor and used handlebar tape to cover the trailer's frame where the floor was sitting. This proved to be a very good solution.

I found existing holes in the rear of the trailer that were perfect to reinstall the red reflectors.

Step 4: Cargo Box II: Sides

The trailer was ready for a test ride. I generally do my grocery shopping at the local supermarket that belongs a popular German discount chain where there is plenty of boxes available. Using a rope tied around the trailer frame I secured the boxes from falling off.

The rope did the job but I decided to go for something more permanent. I bought a mesh and cut it to size and used cable tiers to create the sides of my cargo cage (again, I stuck some handlebar tape between metal parts for noise reduction ). I eventually opted for an open rear to allow for oversize items to stick out from the back (this will prove essential to easily load a bike on the trailer and accommodate all bike sizes).

Step 5: Trailer Top Beam

While I was experimenting different options to load a bike on the trailer, I found that the trailer itself offered a solution I was not considering. The top beam can be released from one end while it hinges on the other end. This allows to pass the beam through the rear triangle of the bike before locking it in place again, so that the wheel hangs high above the ground from the back of the trailer without touching it. An added benefit of this solution is that the trailer becomes and improvised bike stand where you can still rotate the pedals, let the rear wheel spin and make the adjustments needed (e.g. rear derailleur).

To protect from damage the frame of both the trailer and the bike, I applied handlebar tape to the top beam (not my best job: look for online resources on how to install handlebar tape - here is an example)

Step 6: Fork Mount

The current fork mount design is the result of much trial and error and is potentially still evolving (suggestions are welcome!).

NOTE: The T shaped bit of chrome tubing that you can see in the pictures is part of the experimenting process but at this stage does not play any role and can be completely disregarded.

I found that my solution would work best if I could attach the bike's front fork to the trailer as low as possible. I cut an opening at the very front of the floor of the trailer and drilled holes on both sides of the bottom frame of the trailer, so that the threaded rod running through those holes would be passing just under the opening in the floor.

The fork mount consists of nuts, washers and rubber rings inserted on the rod in the following sequence (repeat twice as in picture): nut-washer-ring (space for the fork) ring-washer-nut

Make sure you run the rod through the hole on one side of the frame before inserting the fork mount elements.

Lock the rod in place with nuts on both ends.

Step 7: Load the Bike

Loading a bike on the trailer only takes a couple of minutes.

Remove the front wheel of the bike.
Release one end of the top beam
Spread apart the two couples of nuts on the fork mount
Holding the bike from the saddle with one hand, position the fork on the fork mount
Pass the top beam through the rear triangle of the bike and lock it in place
Adjust the bike position as needed and secure the fork to the fork mount by tightening the nuts
Use one bungee cord(yellow) to exert a downward force to the front of the bike (back up for fork mount failure)
Use one bungee cord (blue) to prevent the rear of the bike to move sideways
Use cable ties or a piece of string to secure the front wheel to the trailer

Step 8: Carry-a-bike With a Bike

The hitch did not require any particular modification. I only changed the size of the nut and bolt that secure the trailer to the carrier bike frame simply to match the size of the nuts on the fork mount. This way I only need to carry a single wrench to load/unload the bike and to attach/remove the trailer.

Overall, it rides very well and the bike on the trailer is perfectly stable. Of the three forces/contraptions that contribute to this stability I think the most prominent one is gravity (i.e. the weight of the bike itself hanging from the trailer's top beam) followed by the bungee cords and then the fork mount. However the combination of all three provide the safest riding experience (you wouldn't want to ride with the concern of a bike coming off the trailer behind you...)

I hope this was helpful and I look forward to your feedback, ideas and suggestions in the comments section.