I built a tallbike for a friend. Unlike most of the designs I’ve seen, my version uses a rear derailleur to offer several (in this case, 5) speeds. I would feel really nervous about riding a tallbike that couldn’t shift into low gear; it’s just too far to fall.
This tallbike was made from 2 donor bikes: a 1970s Raleigh 10-speed (with vintage bicycle registration sticker from 1979!) and a Nishiki Cresta single speed. The bottom bracket for the Raleigh was a little past its prime, so we decided to put the Nishiki on top.
We stripped off all the unnecessary components, and put the frames together. The connector from top headset to bottom headset is a piece of 1/2″ EMT tube.
I’m not sure what the secret is to lining up the headsets, but since I had no clamps or flat surface to work on I had to come up with my own method. The result is the small crook you see in the connecting tube. The result seems to be within 1/8″ of perfect, which is amazing for an entirely freehand process.
In order to fit the derailleur into the new chain path, I had to weld one of the spring-loaded sections solid. Since only the rear gears would be used, there was still enough play left over to handle the difference in chain length.
This is the chain setup. Note that the rear brake and the cable to the derailleur have not been connected yet.
The rear derailleur is welded to the rear dropout.
The front derailleur is just there to keep the chain aligned, and its position was set with the limit screws.
This is the bottom of the linkage between the top and bottom headsets. The reason for the odd shape is twofold. First, the ugly bit is 2 plates that were welded together to align the 2 bikes. The odd-angled tube is there to allow access to the headset bolt. This proved to be very handy after the first night of testing, when it needed to be tightened!
So far the only mistake in this design is that the weight is mostly over the rear wheel. This will probably be fixed by using a smaller front tire and/or fork.