Another Homebrew Bakfiets (or Cargo Bike, If You Don't Speak Dutch)

I ride bicycles. In a densely populated city like Jakarta where the traffic jams will never make sense, riding bicycle is the best way to go. Some might say riding bicycle in Jakarta's crazy traffic is insane, but let's keep that story for another time.
Owning a bicycle shop means sometimes I have to carry bicycle parts across town. In some cases, even frameset(s). While wheel(s) can be easily strapped to backpacks, messenger-style (providing it's big and versatile enough), carrying framesets or bicycles are another set of challenge. Resorting to motorcycles? While that sounds like a good idea, I still prefer carrying stuffs with bicycle because the running cost will be cheaper. And it's another way to advertise my small bicycle shop.
Enter the bakfiets. Or longjohns, as some may refer to it.
Two-wheeled cargo bike is preferred because while three-wheeled bikes could haul more stuffs, they did it by sacrificing the manuverability. I also go with front-loading because it's easier to manage in traffic, all with the low center of gravity and stuffs.
While three-wheeled cargo bikes are a bit more common in Indonesia, it's not the case with two-wheeled ones. Buying one from overseas will costs me a hell lot of fortune, all with shipping dimension and weight. So if one of the goals was to advertise my shop, why not building from scratch? In Jeremy Clarkson's words, how hard could it be?
So here's a not-so-well-written story about how I built my homebrew bakfiets. It's homebrew, because apart from the welding process (I don't have a welding machine in hand), I built it entirely on my home-slash-bicycle shop. Some language barriers might be found since English is not my primary language. I also didn't put much pictures of the process (only the results), since I didn't always have camera (or phone) in hand.

tl;dr, here's how I built my cargo bike!

The bakfiets was built from a steel donor bike with steel tubing extension on the front. Steel is chosen because of its price and availability, and also it's easier to work with.
Coming from a design background I figured some essential aspects regarding geometry. They are:

1. Fork trail.
Long story short, the trail length should be short to keep the steering stable yet agile enough. I didn't have the privilege of fabricating my own fork, so I have to modify a BMX fork (see "Ingredients"). Having good experience with touring bikes with 50-60mm of trails, I chose to run 51mm of trail on my design. Factoring this and the fork offset on the BMX fork, I got the headtube angle set at about 71,5 degrees. A bit slack.

2. Bottom bracket height.
To keep it stable on high and low speed, I make the bottom bracket height as low as possible. I ended up with about 289mm. You might want to get lower, but keep in mind that if you're using large rear wheel on your donor bike, a bottom bracket that's set too low will disrupt the riding position (the seattube angle will be too steep).

3. Wheelbase.
Imagine this bike as a bridge that suspended between the two wheels. You can go bananas by making the bike as long as possible, but you might ended up using bigger or thicker tubings to prevent the whole bike from sagging under heavy load.

Here's some of the ingredients I use for my bakfiets:
1. Steel mountain bike frame. A disc brake compatible model was chosen for extra stopping power. Derailer mount is a plus.
2. Steel BMX fork with 1 1/8" threadless steerer.
3. 16mm x 37mm square-section steel tubing, 2mm thick. I ended up using 9 meters of it.
4. I used 42mm steel pipes for the headtubes (front and rear) because they have internal diameter of 34mm, roughly the same as the outer diameter of 1 1/8" threadless headset cups. You might want to use thinner pipes for this purpose, as long as the internal diameter still be 34mm.
5. Some scrap 5mm steel plates or strips to make steering rod mounts and front brake caliper mounts.
6. I found an adjustable rod with heim joints from our local scrapyard, probably taken from a car or something. The heim joints are used for the steering rod.
7. 15mm steel rod, for the steering rod.

Once again, I deeply apologize for not being able to give you step-by-step pictures on the building process. But here's a couple things I learned along the way.
I'm using two parallel downtubes to make building this bike easier. I thought I can get away without jigs, but turns out I was wrong. Make sure you check the alignment between these components before you weld them:

1. Front and rear headtubes, before you weld it to the donor bike. Check for vertical alignment. Don't weld the cargo bay just yet.
2. Front and rear headtubes, checked from the seattube and rear dropout. Check for vertical and lateral alignment.
3. Make sure that the front and rear wheel tracked on the same center line laterally. Also check the vertical alignment.
4. If everything's well aligned, weld the tubes that formed the cargo bay.

The second headtube was set in 90 degrees angle to maximize cargo area while retaining short wheelbase. It doesn't affect steering that much.
The second headtube needs a steerer as well. A looong steerer. I cut both legs from an old fork while retaining the fork crown race mount, cut the steerer in half, then reconnect it with 1" pipe to desired length. A strip of 5mm thick plate was welded to make mounting for the steering rod. The stem was set as high as possible for comfort... and you'll never know when you have to brought tall stuffs.
I only used one steering rod on the driveside because the non-driveside fork leg was occupied by disc brake caliper. More on the custom brake mount later. You might want to have some sort of adjustment system on your steering rod because it helps much during steering setting.
Threadless headset system needs the stem to prevent the bearing from becoming loose. In this picture I used an old seatclamp to replace the stem on the front steerer/fork. You might want to use something neat as this part from Problem Solvers.

I used disc brakes on my bakfiets because I need good stopping power. And because I have an old 8" rotor from my mountain biking days left unused.
BMX forks doesn't come with brake caliper mounts, so I made it myself from 5mm thick steel plate. The caliper mount was then brazed into place.
Another problem is that the front brake caliper is way too far from the brake lever, so I use hydraulic system. Even stock 210cm brake hose commonly found on pre-bleed hydraulic disc brake systems was not long enough, so I replaced it with this long hose kit from Jagwire. I ended up using 240cm from the 300cm supplied hose.

Twin downtube design prevents me from using double or triple chainring due to clearance issue. That's fine, because I'm using internal-geared hub drivetrain on my bakfiets.
Internal-geared hub lets you to shift even when you're stopped completely, good when you're stuck behind a car and needed to restart your cadence.
I'm currently using 36/18T chainring/cog combo on Shimano Alfine 8-speed hub. This combination provides balance between low gearing for climbs and heavy hauls, and it doesnt't leave me spinning crazily on high gears. The jumps between gears felt a bit steep, though.
Oh, another hack. Since Shimano Alfine parts are kind of hard to find in Jakarta, I have to improvise to get the 18T cog to replace the stock 20T cog. I ended up modifying Shimano MX66 BMX/singlespeed cog to fit Alfine's cog mount.

You'll need kickstand for your bakfiets. Some might want to make custom ones located underneath the cargo bed. They provide better stability. I'm too lazy to make them, so I used a double kickstand instead. The stood up nicely so far.
The frame weighs 12 kilograms. Just for the frame. I reckon the whole bike weighs about 25-30 kilograms... so I didn't make wooden box for it. I ended up using 100 liter plastic container box when I need to carry stuffs like groceries or anything else, strapped to the wooden bed with used tire tubes.
While narrower handlebar might help you swerving around in traffic, I've found that trail-width mountain bike riser bar (around 730-750mm width) suits me well, especially when I have to carry wide loads.
I once carried two persons on the cargo bed. With me on board, we all weighed around 180 kilograms or so. The bike survived, but I'll never wanted to do it again... because I can literally see the frame sagged under load. No permanent damage, though.
I've spent around US$500 for this project. Most of the budget are used on the Shimano Alfine hub kit and Shimano Deore hydraulic brake system. The donor bike was bought second hand, and the wheels are built by yours truly.

If you want to see this bike in action, check out the #homebrewbakfiets hashtag on Instagram!

Thank you for reading!