Single wheel bicycle trailers are commercially available, but may cost $500 or more. This one was put together for about $50 in used parts and a few hours of work. I made it at TechShop, and so can you!
Step 1: The Basic Layout
The plan calls for taking a front bicycle fork and wheel, and attaching a rear rack to serve as the basis for the trailer carrier. The bike will be connected to the fork with a universal joint and a piece of electrical conduit.
Step 2: Bolting the Rack to the Fork
The first part of the project is basic bicycle mechanics, mounting the bicycle rack. However, the rear rack was not designed to mount on the front forks. The flanges of the fork needed to be drilled in order to fit to the bottom ends of the rack. Further, the top rack bracket needed to be bent in order to attach to the forks.
Here are images of the front fork drilled and bolted, and the top bracket before, during, and after being bent to fit.
Step 3: Fitting the Bicycle Stem to the Seat Post
The next task is to repurpose the bicycle stem as the seat post clamp for the trailer.
As shown, the bicycle stem was cut in half, leaving the clamp mechanism for the seat post and the cylindrical end to fit into the electrical conduit.
The stem was too large to fit into the electrical coupler and needed to be sanded down. As shown, the stem now fits into the coupler.
Finally, the stem was drilled so that the existing conduit screw acts in sheer instead of being just a clamp.
Multiple strips of soda can were used between the stem clamp and the seat post.
Step 4: Mounting the Universal Joint Into the Couplers
The next task is to fit the universal joint into the electrical couplers at each end. In this case, the coupler was too small and needed to be shimmed.
Plumbing caps fit snugly over the universal joints but needed to be sanded down to fit into the electrical couplers.
With the plumbing caps sanded down, I then drilled through the couplers, the plumbing cap shims, and the universal joint to insert bolts. Shown here are the pilot holes drilled and the bolts in place but not yet tightened.
The universal joint used was purchased from McMaster-Carr for “Slow Speed Use.” In the final use of the trailer, this universal joint had too much play. For about the same $15, a more precise universal joint could be found at an automotive scrap yard as part of the steering assembly for a small car.
Step 5: Bending the Electrical Conduit
The next step is to bend and cut the electrical conduit.
First measure the length of the conduit to be left straight for the bicycle fork to fit into.
It is essential to have the right tool to bend electrical conduit. As shown, attempting to bend the conduit around the wrong mandrel resulted in kinking the tube.
However, using a conduit bender produced a nice smooth curve.
Step 6: Cutting the Electrical Conduit
Leave more conduit than you need and trim it to fit as needed.
Shown is the trimming needed to allow the bicycle stem to seat fully. Each hacksaw cut can be cleaned up with a file to make the edges smooth and flat. As shown, masking tape is used as a guide for cutting.
Shown is an amusing image of the top conduit prior to cutting to length. This eight foot long trailer could be used to display an advertizing banner, such as “Come Visit TechShop!” or something similar.
Shown also is an image of the trailer cut to a more reasonable length, and then trimmed again to an aesthetic length.
Step 7: Final Drilling and Bolting
Only a couple of additional parts are needed to be drilled and bolted for final assembly.
Shown is an image of the forks being drilled. A level was used to ensure that the conduit was parallel with the rear wheel.
The last hole needed to be accurately drilled to ensure that the trailer wheel would line up with the bicycle wheel. Shown is an image of this alignment.
Finally the trailer is bolted together and ready to ride!
Step 8: The Test Ride
During the test ride, the unloaded trailer had almost no rolling resistance.
What is interesting is how much tighter a circle the trailer makes than the bicycle.
In contrast to standard panniers, where rider heel clearance is always an issue, large or bulky items could easily be carried on both sides of this rack.