Cargo Bike Attachment

Why a cargo bike? The answer is simple, it's a private mode of transport that allows most urban people get from point a to point b with all of the stuff we need that is truly zero emissions. In the US over 1/4 of the trips we make are less than 1 mile, but we drive because we need the cargo capacity. With a cargo bike we can travel several miles and still get all the groceries we need, or take the kids to school with their book bags, instruments, and science projects. In addition to the utilitarian aspects of the cargo bike, it is also a way to be more active and healthy. Approximately 70% of the people who ever try a cargo bike find someway to incorporate it into their daily lives.

Unfortunately, cargo bikes are very expensive in the US. It is hard for many people to commit $2000 - $6000 for a cargo bike. The goal of this instructable is to provide instructions on how to build a tadpole cargo trike for around $300.

There are a lot of instructable out there that show how to sacrifice a bike or two and turn them into a cargo bike. I had the vision of a cargo bike attachment that can be added to your existing bike allowing you easily switch between your regular bike and a cargo bike with ease. The idea is that you could drop the kids off at school or daycare, leave the cargo attachment locked up, and cruise to work on your regular much faster much lighter bike.

This project was a lot of firsts for me. First time using Autocad, first time welding, first time using a vertical mill, and first time using a lathe. There is no way I could have successfully finished this project without the help of some friends and faculty at the college I go to. So a big THANK YOU to Steve and John, and of course to my professor, who was also supportive of this crazy project. In the past I have spent most of my time working with wood, and I even contemplated making this project completely out of wood, but in the end steel was the better material.

I hope you like my project and feel free to leave some comments below. If you have an idea that would make this project better for the next person, please don't hesitate to let us know. Cargo bikes are growing in popularity in Europe and are starting to catch on in the US. In a few more years I think you will see the numbers of cargo bikes increase.

I have attached the DMG file from autocad. So if you have autocad you should be able to open this file and explore, make adjustments, and see the precise measurements. If you don't have autocad, I will do my best to give precise measurements along the way.

The bike will connect to the attachment at two points. The first point will be with a fork-mount that is attached to the steering system and the second point will be back by the bottom bracket where you would normally mount a kickstand.

The most complex part of this design is the steering. With many cargo trikes the whole front compartment pivots. This is not so easy to do with the attachment, because of the angle of the headtube on the bike. As a result, and after a lot of research, I decided to make the bike steer like a car using ackerman steering. So when I turn the handlebars they rotate a cam under the frame that pushes and pulls on the two front wheels. This will be covered in great detail later.

A big part of this build was to be as environmentally friendly as possible. That means that if I could repurpose or use little bits of steel instead of virgin material this was a must. I spent a fair amount of time digging through the bins looking for the little scraps and pieces that would work for my project. This also helped me keep the cost down since they sell the scraps for less, usually by the pound instead of by the foot, and you don't have to pay them to cut it for you if you don't have a truck.

Material list:

6' - 2' square pipe (next time I would probably use 1" x 2" pipe)

1' - 1/2" angle iron

6" = round pipe with 1 1/4" ID

~5" - 1" steal bicycle steerer tube (I ordered this from a bicycle frame supply website https://framebuildersupply.com/collections/steerer...)

6" - 7/8" tube

4 - 1 1/4" oil impregnated brass bushings

1' - 1" x .2" steel flat

~ 6" x 7" steel plate about .2" thick.

4 - 1/2" rod end bearings (Jegs.com had the best price for these)

4 - 3/8" rod end bearings (2 RH thread and 2 LH thread, I didn't do this but I should have)

1 - Bicycle fork mount (easy to find on amazon)

2 - 20" wheels with sealed cartridge bearings. I stole mine off an old burley bike trailer.

4' - round tube with about a 5/16" id. (this will be tapped so the 3/8" rod end bearing can be threaded in)

Misc. Nuts and bolts

I cut the pieces for the chassis which consisted of one long 55" tube and two 11" pieces.

Weld the horizontal members 15" from what will be the front of the cargo attachment.

On the end of the horizontal members, I welded the 1 1/2" angle which has a 1/2" hole drilled 1 5/16" from the front on top and 1 5/16" from the back on the bottom. (This is to give the wheels caster when you turn, just like a car. This setup will provide with about 10 degrees of caster.)

When you are done you will have a 6' steel cross. Yes people are going to make some jokes, so I hope you can bear it!

For the steering there will be a tube that runs through the chassis. On the top side of the tube, there will be the fork mount and the bottom side will be the mount for the tie rods. For now we are only going to focus on the steel tube that will be welded into the chassis.

The tube should be 3 3/4" in length and have an I.D. of 1 1/4" so that the Brass bushing can be inserted. The Pipe I had was a little too narrow for the inserts, so I put them on the lath and used a boring bar to reach the desired I.D.

With this done I needed to drill a hole in the chassis at a 70 degree angle. This angle is to match the angle of the fork going through the head tube which is 68 - 72 degrees on most bikes. I used a boring bit on the mill, but I think it would be easier to use a hole saw that is the same diameter as the pipe, which in my case is 1 3/8". I also think you could do this by hand and then go at it with a file to make it fit. If you go that route make sure that you get it square, otherwise the bike will lean when you connect it.

Last, weld the steering tube in place. I did an even spacing on top and bottom. Be careful on this part, if you overcook it you will warp the steering tube and your bushings will not easily fit like they did before. However, if the steer tube dose warp, go at it with a dremel until you can again slide the bushing into place.

This part is made up of several pieces.

On top will be the 5" x 1" steer tube that we ordered from framebuildersupply.com. welded to this is a plate for the fork mount to be bolted to. Since the rake on bicycle forks varies widely this plate will allow you to move the fork mount back and forth so that the head tube of the bike aligns with with the steer-tube in the chassis. I had a friend cut this part out on a CNC plasma cutter.

I also welded a sleeve to the bottom of the plate this makes a flat surface to rest on the bushing. When assembled this part will fit inside the tube and bushings we welded into the frame. It is held in place with two lock rings.

On the bottom side there is a 3" x 7/8" od tube with another plate, that was also cut out on the CNC plasma cutter, welded to it. I stole a wedge nut from and old stem to mount this part which slides inside the 1" steer tube and is then tightened to hold it in place.

We'll see the final assembly of this in a few more steps.

The specs for both of the parts that were cut on the CNC are in the DWG file in step one.

For this part I started with a 2" long piece of @" square pipe. so I wound up with a square cube. On the top and bottom I drilled a 1/2" hole offset by 1/2" and on the sides I drilled a 1/2" hole dead center.

For the axle I used a 1/2 bolt, and found one that had about 4" that was non threaded. It was a 10" bolt that I cut down to about 6" long.

Finally I added the piece for the steering connection. For this I used 1" wide x .2" steel flat iron. I cut it about 3" long and drilled a 3/8 inch hole one one end and two 1/4" inch holes for mounting on the other end. It was a tight fit and I thought that I might want to play with the length of this piece if the steering needed fine tuning, which is why I decided to bolt the piece on instead of weld. In the end I had a 1" tab to mount the rod end bearing to. This gave me a 1:1 ratio for the steering which ultimately has seemed to work well for me.

Now that you have made most of the pieces it's time to put everything together and make sure it's all going to work.

First I started with the wheels.

I put on the lever that the tie rod will connect to, this is the last part we made last in step 6.

Then I ran the axle through the wheel and used washers to space the wheel away from the wheel mount. Otherwise the spokes would hit the wheel mount and break the wheel.

Then I loosely added the 1/2" rod end bearings that will connect the wheel to the chassis. Here I kept adding washers until the rod end bearings were level.

The next part is to assemble the steering mechanism. This is fairly straightforward. First, slide the upper mounting plate through the frame slide on the spacer and then the two locknuts. They should be tight enough to keep the plate from sliding up and down but not as to restrict the piece from turning. The lower mounting plate then slides inside of the upper mounting plate assembly and is then tightened down. This should be tight enough that it can not turn separate from the upper mounting plate.

From here I snugged everything up and was able to start finding the length for the tie rods. To do this I simply measured the distance from each rod end bearing. I also wanted to make sure that I had roughly 1/2" of thread showing so I had room to make adjustments. With my final length I cut the tube with 5/16" ID to the length and tapped them with a 3/8-24 tap. If you are new to tapping threads I recommend watching some Youtube videos, it is really easy to break the tap and they can be expensive. Steve showed me a trick putting the tube in a vise on the drill press and the tap in the press and then turning the press by hand (do not turn on the press!). This helped get the threads started square.

I used all right hand threads for this part but it is easy to find LH threads as well. For ease of adjustment you could do a RH on one side and LH thread on the other and then be able to adjust the tie rod without having to disconnect one of the rod end bearings.

The first part of fitting the bike is to connect the fork mount to the fork mount plate, I kept the bolts loose so I could easily slide the plate front to back.

Then I propped the back of the attachment up so the chassis was sitting level.

After connecting the bike to the fork mount I needed match the angle of the head tube and steering tube and line them up. If they are offset and angles don't match up it won't turn or something will break, so take your time.

Once I had everything lined up found that I had just over a 2" gap in the back, which was a little larger than planned because I messed up the fork mount plate. so I found that a scrap piece of 2" worked well as a spacer and then I added a few big washers under the chainstay.

I cut a 7/8" tube to the same width of the chainstay and drilled a 1/2" hole through it then I drilled a 1/2 hole through the chassis and bolted the chassis to the bike frame.

Note: I did have to tweak the length of the chassis, and I actually cut it to short but lucked out by having to add the second piece of 2". So take your time, I was getting to excited to be near the end of the project.

After all that hard work it's time to take it all apart.

This part is pretty self explanatory, I put all the parts to be painted in my kids wagon and all the other parts in this handy little parts organizer.

From there I laid everything out on a table, and hit it all with a little sandpaper, just a quick once over should be good.

Then I cleaned it all up with mineral spirits. I found this "Klean Strip" biodegradable stuff at Home Depot and it worked fine.

Then I primed everything with Rustoleum self etching primer.

Once the primer dried, I painted it all with Rustoleum automotive paint and let it dry for a couple of days.

Now that your paint is dry you can reassemble the cargo bike attachment.

This is pretty much the same as step 7. The big difference is this time I used Nylock nuts and Threadlocker Blue.

For the front cargo area I used U-bolts to attach an old Burley Bike trailer I had. But you can make whatever suits your needs. I even toyed around with putting a wheel barrow bed up front. Or a light weight aluminum truck box that locks.

Once it was all together it was time for a test ride!

Things I haven't done yet are find a way to mount brakes to the front, although it stops pretty good with only the back.

Have fun and don't forget to wear you helmets!

Thanks for checking out my Instructable! Please give me lots of feedback, how can this be better? My dream is to see more people riding cargo bikes and fewer people driving cars.