Ever since visiting Amsterdam I've been itching to make a bakfiet or cargo bike. For about 2 years I've been using a kids bike trailer reinforced with steel and a wood top. I got that idea from the Mr Money Mustache Bike Trailer post. Every time you use your bike to do a simple errand you are not driving your car and saving money. You are also an instant bicycle advocate and get to answer questions like: You rode here? You're going to put all those groceries in your bike? I followed the instructable REcycle 2 wheel cargo bike and painted the frame with directions from this youtube guy. While professional cargo bikes are amazing engineering marvels, I couldn't justify spending the $2-5K. My hope is that more people make these things and discover just how much you can get done on a bike. I've included a bunch of photos to hopefully help you on your journey.
There was some restrictions in my build. I wanted it to be around $500, short enough to fit in my shed, long enough of a cargo bay to hold a car seat and as low maintenance as I could make it.
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Step 1: Get Your Bicycles
I am fortunate to be a part of a bicycle coop. They have a steady supply of used bicycles. I used a magnet to find the steel ones in the scrap metal pile. I chose a steel 26" wheel womens bicycle because it had a step through frame. I wanted to be able to quickly jump off if the bike started tipping under load. The womens bike had a drive train that worked. The front fork was cracked and so we couldn't use it at the coop. I also found a kids 20" bmx bike with a stripped bottom bracket. This bike was unusable but the headset was still good. I then found a bunch of other chromoly frames to use. In all the cargo bike is made from 6 recycled bicycles.
Other supplies that I had to get/ buy:
chromoly tubing for main tube
steel L beams for box base
steel tubing for kickstand
screw rod end LH/RH thread and welded bung to put in steering tube
I found the rod ends on amazon and bought the tubing from a local company that specializes in making racing roll cages. You can get away with very thin walls, but make sure you let them know it is for a bicycle. Motorcycles and roll cages have specific thickness requirements that are very heavy for a bicycle.
Step 2: Grind and Weld
I found a local hobbyist that tig welds recumbent bicycle frames. He worked in the auto fab industry for years. He patiently worked with me through my plans and diagrams. The car jack and chain was used to bend the chromoly tubing up to our 70 degree angle.
There's some design components that are very important.
1. Bottom bracket height, you want the main beam to be level with the ground, but you also want the bottom bracket to be high enough that your pedal won't strike the ground.
2. Straightness of the frame. This was very hard and requires a good jig, we measured several ways, including the back axle to front beam to make sure both sides were the same. If the frame is not straight the bike will ride poorly.
3. The front fork angle should be around 70 degrees, more of a rake will make the steering mushy and too steep will make it twitchy. You can look at touring bicycles for an appropriate angle.
4. Front wheel clearance. You need that front fork angle to be correct, but you also need the front wheel to clear the frame behind it.
5. Make the steering rod so it still utilizes headset bearings and can be removed to repack those bearings.
6. The brakes on most bmx bikes are terrible, we cut off the yellow cantilever brake posts from another bicycle and welded it to the 20" fork. If I had more of a budget I would have purchased a solid steel 20" fork with disc brake mounts. Welding on those mounts was out of the skill set for us at the time, but might be worth doing later.
Step 3: Little Bits
The steering rod was bent to allow left turns, the ratio of length from centerline for the front steering arm to rear steering arm is 1.3. The longer length in the rear steering arm allows a greater throw of the front steering per input to the handle bars.
The main head tube is actually an old top tube that we hammered in a headset bearing cup that would accept a bearing race from above and below. It is basically a really long head tube. We took an old threaded fork top and welded it to a section of pipe. That pipe runs down the main head tube. We welded part of a bottom bracket to the pipe. This allows the bottom of the pipe to accept a bearing race and fit nicely into the bottom bearing cup of the large head tube. Since it was a bottom bracket we could screw in a crank arm as the rear steering arm. You can look at other instructables, but the biggest take aways are your head tube has to be able to accept bearing cups on either end, and snugly fit the steering fork with enough threads out the top to screw in a headset cap. This might be easier if you used a non-threaded stem.
The rear steering arm then moves with the handle bars and pushes or pulls the right side of the front fork.
The second top tube down was bent to allow easier welding areas around the main head tube. Bondo was used to smooth out any joints and sanded. We forgot to tape out the bottom bracket, so we had to clean it with a brass brush. You also want weeping holes for any moisture to drain out.
The kickstand was very hard to figure out. The angle pictured is way too far forward. A 5 degree angle is all that is needed. The extreme angle here makes it very hard to shift the bicycle forward with a heavy load. We used a gate latch to hold the kickstand up. The gate latch tends to open on big bumps, so I put a keychain carabiner in there as a safety backup. I have seen rare earth magnets, clips or springs to keep the kickstand up when not in use.
Step 4: Paint ...think Before You Rattle Can
You are going to need to prime your bike to avoid the rust. First we removed all stickers with a heat gun and plastic scrapper. I used a gray primer so I would be able to see where paint eventually chipped so I could avoid rust.
Then you need to assemble your bicycle to make sure everything fits and it doesn't need more welding.
Then you strip all the parts off and start the multi-day process of painting. The hardest thing is to wait long enough between painting to let it dry. Wet sanding with 1500 paper is a must. Then you put it back together and ride.
All in all, I would not paint it myself next time. Painting in my backyard was difficult at best. Bugs, dust and plants got in the way. This is a $35 paint job and good from about 12' away. Next time I would powder coat it or try talking to an auto body shop to see if they could cut me a good deal.
Step 5: Final Thoughts
Overall I'm very happy with how it turned out. The bike weighs in at 80 lbs with the wooden box. I intend on traveling 5 miles max per ride. I want this bike to remove any excuse to jump in the car for little errands. After riding it for a bit, I want to put a rack on the back, fenders, and chain case so it is all weather. Also bicycle tires are only rated for a certain weight and I've exceeded that several times. Look for tires that tandem bicycles use as these weights are comparable. If I turn too far left the steering rod hits the front wheel, too far right when parking and the front wheel can spin around completely. I plan on adding limit stops to the rear steering arm to prevent this. Additionally, I'm going to build up a stronger back wheel with an 8 speed internal hub. You need very easy gearing and I think that will be the best way to accomplish this. I may post an update after I get the bicycle dialed in the way I want it.
I hope this helps and motivates you to start one of your own.