Even though almost all new mountain bikes now have just one chainring and no front derailleur, it would still be nice to have all those other gear ratios again. The Binary Gear is designed to bring them back, without reintroducing a front derailleur.
Currently the subject of a Kickstarter campaign, the Binary Gear is manufactured by Italian bicycle tech company MagneticDays.
The device – which comes with a system-specific set of adjustable-length cranks included – replaces a bike's existing bottom bracket. Of course, it could also simply be built into new bikes. For now, it's only compatible with bicycles that have a PF46 or T47-type bottom bracket.
Instead of simply incorporating a single axle that runs through the bottom bracket between the cranks, the Binary Gear features a 2-speed mechanical gearbox. At one speed, crank revolutions are translated into chainring revolutions at a 1:1 ratio (just like they normally would be). At the other speed, however, that ratio climbs to 1:1.25 – so in other words, the chainring revolves 25% faster than the cranks. "
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