Continuing where we left off, we will start with the more fun part of welding on the cargo bed area. If you missed the first part you can find it here.
Welding the cargo bed.
Like mentioned before. The bike’s geometry is made from points, what comes between them is only aesthetical. So this part was quite fun as everything that mattered had been aligned and locked into position. The only thing you need to worry about here is that you have enough space for pedals and the front wheel.
New steerer, fork modifications.
After this step, you will notice the progress stopped. The frame was left unfinished for almost a year before having time to continue. As a next step, all the excess was cut off, and the head tube [guide to frame tubes] shortened. Also, the fork got modified to fit 20″ wheel as originally it was meant for 700c wheel, and disc brake mounts added. It’s important to check that you don’t make the fork too short or too long, so the cargo area will be parallel to the ground. Now I finally also cut away the extra parts of the down tube and fitted a new steering tube. I went for A-head stem for this. This bike was an experiment and I didn’t want to spend time and money ordering specialized fancy tubing. So I found some precision tubing that fits the stem and the headset from Onninen. It is quite heavy with 2 mm walls, but as I knew I would make it an e-bike, the weight was not too big of an issue. Improvements for next time: Go for Chromoly steerer and head tube to save some weight. Order early in the process.
Outsourcing lasered parts.
Now you could do this on your own, but I saved a lot of time and also made things look nice by ordering some of the parts laser-cut like fork dropouts, steerer end, bearing holders for steering arm, etc. You can find my DXF files here if you find them useful.
The finishing touches.
At this stage, I bolted on a bottom bracket, cranks, an old chain, and went for a test ride. Everything felt nice, so the only thing left was to weld on last tubes, disc brake mounts (you can find mine under the above link), cable holders, kickstand, and then it was time for the paint shop.
After everything arrived from powder coating, it was finally the time to assemble everything. All went smoothly and the bike was in one piece in no time.
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HOUSTON, WE HAVE A PROBLEM! (and cure)
Early testing revealed some flaws I had described in the last post about handling. After hitting 30 km/h the bike almost always got hit by speed wobble. With this problem, the bike would be rendered useless. Luckily I didn’t get discouraged as even the guys at Larry vs Harry also seem to have a problem with this, and the cure is to add a steering damper like the one used on motorcycles. I ordered one and attached it to the bike, and.. ..it solved the problem for a while before it broke down and leaked all the oil out after just 600 km on the bike. Then winter came along and I left the bike unused until this spring. After talking to some other frame builders I heard that this problem was common, many of them had also been fitting their bikes with steering dampers. The problem seems to be that the front end just gets too light as the problem is less evident with cargo on the bike. Anyway – I set to work early spring and made new damper fittings that would increase the working range of the damper. Having now done 500 km at speeds of 35 – 60 km/h without any steering wobble it seems that the bike is finally finished. Improvements for next time: a.) Design your bike with steering damper in mind from the beginning. b.) Keep shallow fork angle, short fork rake, and thus a large amount trail. This may improve stability if you want to resist using a steering damper.
To summarize, this project turned out a lot better than I had anticipated. Before setting to work, my mind was set at 50/50 chance that the bike would work as well as it does. The Bafang 750w electric unit works well, the geometry is working with the steering damper, there is plenty of cargo space and it goes as fast as you wish. The mileage speaks for itself – currently, I’m averaging 150-200 km per week and only use the car for a short ride once a week to keep the brakes from sticking, etc. So if you have some welding skills and you’re thinking about building yourself a cargo bike- GO FOR IT! Also as a side note, we are constructing a jig to weld some more frames, so you will soon be able to order a proper cargo bike frame from us 🙂
And here it is – doing 45 km/h:
Nighthawk Cargo Bike
The styling of our Nighthawk Cargo Bike is inspired by the iconic F-117 Nighthawk stealth plane. The idea has been to have a bike that is capable of carrying as much as a car and to still go as fast as a road bike.
Whether this bike will be for carrying kids or goods, we have a standard frame solution ready for you. However if you would like the cargo bed to be wider, shorter or anything in between, we are open to modifying the design to suit your needs. If you have been to a bike fitter then we can even customize the whole geometry for you, after all this frame is made inhouse – start to finish.
Book your free test ride here: kpcyclery.com/test-ride/