Longtail Cargo Bicycle (reversible, Bolted to Frame)

This longtail build is a development on the reversible and no-weld longtail cargo bikes I found in various forums, which use the homemade / DIY XtraCycle idea.

My contribution here is to develop a strong and stable pannier rack while still keeping the possibility to reverse the build into the original bicycle. That means you could use a much more expensive or more functional bike to start with, e.g. an electric bike. This way you can also get around the difficulties with welding on the chromoly steel or aluminium used in bicycle frames.

You'll still need welding equipment for making the pannier rack. Welding the rack makes it a much stiffer module, which mitigates the weakening influence of fastening it to the frame with bolts. This makes for a reasonably stiff frame and a more stable longtail bike.

I made my longtail bike for taking my two kids to daycare and occasionally transporting cargo. Compared to two- or three-wheeled box bikes this one is more compact and easier to make. The rack is strong enough to carry an adult if needed, although the low height makes it a bit awkward for an adult to sit on.

Equipment:

Mig-welder, power drill and basic garage tools: Screwdrivers, pliers, metal saw, spanners, files, angle grinder, bench grinder, bench vise.

Material:

2 m of 13 mm steel pipe,

2 m of 20 mm steel pipe (I got mine pre-bent from a discarded sleigh shovel)

2 m flat iron bar 30 x 3 mm

24" donor rear wheel

Rear triangle from a cheap full suspension 24" youth bike

~0,5 m aluminium bar 20 x 20 mm (steel will also work, but is heavier)

2 m brake cable, 2 m gear cable (the standard length was just enough)

Two bicycle chains

Screws, bolts, small hooks

If used for carrying children, add:

Used bicycle stem and handle bar

One U-shaped wall hook for handle, 23 x 21 cm

One 90 degree metal bracket for backrest, about 15 x 15 cm (eg. a window sill bracket)

Clear polycarbonate plastic sheeting (protecting the kids feet from getting into the spokes)

Start by examining the bike you're starting with. What size wheels does it have, what type of shifters and where are the possible attachment points for the rack. My bike is a 26" mtb, so I decided to use a 24" rear wheel to lower the center of gravity for the build. You could also use the original rear wheel to reduce the parts needed.

The donor bike (pictured) is a cheap full suspension youth bike, I bought it in bad shape for 10 euros. The main bike is an 90's mtb with Shimano 3x7 gears and cantilever brakes (I forgot to take a pic of it before starting). The important part here is to make sure the bike parts you need from the donor bike will be compatible with the main bike (like number of gears, type of shifter, dropout width and brake type).

Find all the attachments points to the rear of the bike. If it has disc brakes you can't use the attachments to the bikes brake posts, like you could on a bike with rim brakes.

• Dismantle the donor bike, so that you are left with the 24" rear wheel and the rear triangle module
• Remove the rear wheel from the main bike and attach the bottom bracket on the rear triangle module to the rear dropouts on the main bike, using the bottom bracket axis (I left mine free to rotate, but you could weld it stiff to increase stiffness
• Then use a square bar or pipe to connect the damper attachment bracket on the rear triangle module to the bottom bracket region on the main bike.
• If your bike has a bracket for attaching a kickstand then that's a perfect endpoint for the square bar. My bike lacked one so I had to make a custom attachment to the chainstays. I added pictures of the attachement, if you want to copy my way of making it. The piece with the two holes comes from a wire rope shackle (see pic for reference), I threaded an M6 bolt to it with a piece of pipe for distance and used it to brace the M10 through-bolt so that the whole attachement won't slide forward when the frame is under load.

Now you got the basic structure done for the longtail build.

I chose to fit the rack-parts on to the bike one by one, spot-welding them to fix all the parts together, and later adding welds as needed to the rack while having it removed for better access. Welding so close to the bike frame could damage the paint finish on the main bike (although I didn't notice any such), so if you have an expensive bike you might want to use a different method.

Since I wanted the rack to be removable, I had to make a custom fitting to the rear dropout threaded M5 holes, and this was quite tricky with the mig, as a bonus I worked outside in the dark. I wanted the load to lay mostly on top of the rear dropouts and not on the tiny M5 bolts, you can see my solution in the cutout picture from the finished bike.

I don't have pics of all the steps in the welding, but you get the idea, start with the front and rear and add struts as needed to the attachment points. The bench vise was in frequent use to flatten pipe ends and make bends to align parts with attachments points. One important part of the design is having the rack go all the way behind the rear wheel. That way I could add cross-braces between the sides in the rear, which increases the side-to-side stiffness of the rack a lot.

When you are done spot-welding, remove the rack and add welds as needed, then clean it and paint it.

The standard 2 m gear and brake wires were just long enough for the frame, I put one 7-speed chain and half of another one together to get the chain long enough. Google "determine bicycle chain length" if you need, I used Park tools video for this. I also made a chainguard.

Because my bike is for carrying kids I added handlebars, foot pegs, side basket holder, and later a backrest. I'm planning to also add some clear plastic sheeting to the sides to protect feet from getting into the spokes. The garage hook made a decent rear handle, it was reinforced with metal plates welded on. I threaded the attachment holes on the rack, so the hook can be removed when transporting cargo on the bike.

The other holes in the flat bars on the rack are for attaching the wood board which comes on in the next step. Some of the holes allow screwing in hooks into the underside of the wood board, for securing cargo with rubber straps or rope.

Measure the length and width och your rack and cut a board to size: I took a wooden plank and treated it with teak oil which is fast drying. Attach it with wood screws from underneath, predrill the holes to avoid splitting the wood. The rear fender is attached to the board at its middle, with zip ties in front, an a bolt at the back. The spray guard on the end of the bike is a piece of plastic roofing. I made a steering stabilizer from two springs, mostly for keeping the front wheel straight when the bike is parked or loaded.

If you want to make the backrest, it's just a hole through the board with an angle bracket through, attached with wood screws underneath and a piece of wood screwed to the upper part.

Before you test drive, check the tightness on all the screws and bolts on the bike, its easy to forget to tighten them.

My bike turned out quite stiff with very little side-to-side wobble, I can handle it easily. The weight distribution is good when I'm on it, but walking it with a load is more difficult. The final picture is from a trip to the nearby kids playground. This bike works for my needs, it is light enough and feels secure, like it can hold up and take a bump or two.