Introduction: Single-wheel Bike Trailer From an Old BMX and Wheelbarrow
We have a new bike path opening up in town that will allow me to bike to the grocery store without having to navigate traffic on a busy high-speed road. Yay! I do not have a bike trailer. Boo! But as it just so happens, somebody abandoned a cheap Huffy BMX bike in the neighborhood this summer and while debating whether to fix it up and flip it or turn it into something cool, I landed on the idea of turning it into a bike trailer.
It also so happens that I had the remains of an old wheelbarrow hanging around the garage. Most everything I could reuse except the wheelbarrow itself, which I soon realized would work well as the cargo hauler mounted to the BMX frame. A few simple (NO WELDING NECESSARY) modifications and I should be able to easily combine the two.
I'd still like to add a cover to the trailer a well as some lights and reflectors but for now it's ready to go.
Step 1: Strip Bike
After removing the seat, chain, pedals, and crankset and generally cleaning the bike up, I only had two cuts to make with the Sawzall. The first, cutting off the seat post, was necessary to get the wheelbarrow bucket to sit level on the bike frame. The second, cutting off the forks, was necessary to get the front of the trailer to clear the rear wheel of the tow bike.
You'll see in the picture that I cut each fork individually. That was a waste of time and effort. I ended up cutting the fork just beneath the bottom bearing race of the headset (not shown), so only one cut is necessary. Plus, if I would have left the forks intact, I could have more easily used them in another project down the road.
Step 2: Modify Handlebars Into Hitch
After reviewing the eight thousand ways to hitch a bike trailer to a tow bike here on Instructables and elsewhere, I decided I needed a hitch that would allow the trailer to yaw and pitch but not to roll (a two-wheel trailer would need a hitch that allowed roll, but not a single-wheel trailer). I also wanted a hitch that would easily transfer among my bikes and my wife's bikes.
The BMX's handlebars and steering would adapt to those purposes easily with some simple modifications. First, I bent the handlebars to face forward rather than outward, continuing the U shape. This required a lot of leverage and the use of a hydraulic shop press to get the bars straight; it also resulted in a lot of ugly lawn-chair pipe bends - I only learned about three-quarters of the way through the job that going slow and spreading out the bending force along the bars helps reduce pipe collapse - but at least the pipes didn't split or the welds fail.
Once the handlebars were straightened out, I drilled three pairs of holes toward the end of each bar. Two of the pairs were spaced out exactly the width of an eye bolt, which will become central to the hitch system.
Why three pairs? The forward two, as mentioned, are for the hitch pins while in use. The third will fit one of the hitch pins when decoupling the trailer from the bike. To keep from misplacing the hitch pins, I connected the two for each side with a cable.
Hitching procedure: Remove the forward hitch pin from each handlebar, leaving the middle hitch pin in place. Align the handlebars with the eye bolts and slide them forward until the eye bolts rest against the middle hitch pins. Re-insert the forward hitch pins, clasping the eye bolt between the pair.
Unhitching procedure: Remove the forward hitch pin and place it in the third set of holes. Slide the handlebars back until free of the eye bolts, then re-insert the forward hitch pin.
Step 3: Add Hitch Receiver to Towing Bike
And what of those eye bolts? If they're long enough, they'll attach to each other via a threaded coupler. But attaching the eye bolts directly to the tow bike won't allow for pitching, so I grabbed some leftover conduit large enough to slide over the eye bolts and coupler, cut it to length just long enough to allow for the eye bolts' freedom of movement, and ziptied the conduit to the tow bike's cargo rack. A few more (a lot more) zip ties keep the conduit/eye bolt assembly from moving around. I'm currently in search of a better means to mount the assembly to the bike rack.
At this point I tested the hitch to make sure it was secure enough, to ensure that the trailer bike tracked with the tow bike, and that I hadn't mounted the trailer too close to induce rubbing on the tow bike's rear tire. One drawback I noted at this point that I won't be able to engineer away: The weight of just the unladen bike trailer puts plenty of leverage on the tow bike without me in the saddle, enough to pick the front wheel of the tow bike off the ground. Longer handlebars mounted closer to the tow bike's center of gravity might alleviate this, but for now I'm just going to have to be cognizant of the problem while using the trailer.
Step 4: Prep Wheelbarrow
With the BMX frame modifications complete, I turned my attention to the wheelbarrow. As mentioned earlier, the wheelbarrow was well worn, including a couple sizable cracks in the plastic. The barrow was made of HDPE, so I could have easily repaired the cracks with heat and some melted milk jugs, but I decided to stitch the cracks together.
The process involves first drilling a hole at each end of each crack for stress relief and to prevent the cracks from expanding. I then drilled two sets of holes about half an inch apart on either side of the cracks. After that, using some scrap wire that was thin enough to be pliable but thick enough to offer some strength, I stitched along the cracks as seen in the photos. I found that a pair of needle nose pliers helped draw the wires tight after threading them through each hole, particularly after the first set.
To waterproof the cracks and the holes I drilled, I sprayed some 3M rubber undercoating along the length of the cracks. A couple coats'll do.
Step 5: Add Mounting Hardware
I also had some drilled L-channel in my scrap pile that I decided to use as mounting brackets for the wheelbarrow to the BMX frame. To keep as much weight over the rear wheel as possible (to minimize the leveraging effect noted a couple steps back), I wanted to mount the wheelbarrow as far back as I could. That meant drilling a hole into the rear cap of the top tube for the rear L-channel section and using a U-bolt to mount the front L-channel section.
Note that some welds here would make everything a little more secure. I found that really cranking on the bolts will still keep everything wobble-free.
Step 6: Assemble
Finally, using some inch or inch and a half-long 3/8-inch bolts through the existing holes in the wheelbarrow and then through the L-channel will work to mate the wheelbarrow to the bike frame.
The center of gravity on the trailer is kinda high, but as long as I load the wheelbarrow evenly, it shouldn't be an issue.
And as mentioned in the intro, I intend to add a cover of some sort should it rain on my way home from the grocery, along with lights and reflectors should I have to use the trailer at night.
I also intend to replicate the hitch receiver assembly for our other bikes to make it easy to swap from one to the other.