Hello, folks!
I hope that's the right forum to introduce new bicycle technology, a shifted tooth belt drive with derailleurs. All expert opinions found in the Wed are categoric - chain-style belt shifting with derailleurs is not possible. Patent search I made also hasn't revealed any known designs of shifted toothed belt drives.
Of course, I am aware of 2-speed cassette from Veer. However, I was motivated to make a multi-speed belt driven twin of the derailleur-shifted chain drive.
After some months of work am glad to present first experimental results here. The experts are partially right - the belt is lot wider than the chain, so I could manage integrating a 5-speed drive into the standard frame, and a 6-speed version with slightly increased frame spacing. Nevertheless, 5-6 gears are enough for recreational cycling. 5-speed prototype has ratio spread of 300%, and the 6-speed version is extended to 343%.
5-speed road bike
6-speed MTB
5-speed road bike
6-speed MTB
Both versions have double front pulley with a custom-made front derailleur. The rear derailleur is almost the standard one. 5-speed version is based on triple rear cassette, while the 6-speed version includes additional 4th row. 8-9 speed versions are also possible, if belt OEMs manage to reduce belt width to 9 mm. With actual width of 12 mm it will result in larger Q-factor.
Front and rear derailleurs are shifted synchronously by one rotary shifter based on shift drum. This concept is similar to EGS Synchro Shift system from 1990's. Shifting is easy, and the drum pattern prevents excessive cross-belting (what belts do not like, experts are correct here as well).
6-speed combo shifter
Both bike prototypes turned out to be rideable without severe issues. Shifting is smooth, running is quiet and efficient. Despites plastic-made main components, I could apply full load without any failures so far. The 5-speed prototype has already run more than 500 km on the trainer on complex hilly tracks.
5-speed prototype on the trainer
As intended, the belt drive runs dry, tolerates water, dust, and remains clean all the time. As a bonus to known belt drive advantages, this one enables 5-6 gear ratios without rear hub or front gearbox. Efficiency was not yet measured. From the feeling, it's the same as for fresh-lubricated chain, and way better than I can experience on my old bike with a 7-speed hub.
You can watch on my YouTube channel, how this transmission works.
I would be glad to answer your questions in this thread.
Best regards,
Vitaly aka Dry Mechanic