Patented Shimano gearbox on recumbents
Earlier this year I have written about a gearbox that Shimano has patented in early 2019. I have mentioned there the advantage for recumbents would be low if any. Not only because the gear range is too small, but also because Shimano doesn’t expect the system to be used with electric motors. Another important issue of incorporating this kind of gearbox to recumbent design is its shape and possible position on either recumbent bike or recumbent trike. Let’s have a closer look at it.
The fact is that unlike with standard triple crankset, Pinion gearbox or Schlumpf Drive, the cranks are in a different location than is the chain wheel and it seems that there isn’t enough space right around the crank axle for the chain so the position on the picture seems to be the only one possible. Ugly, uh?!
Also, the gearbox seems to be somewhat too big on the main picture, but we can hardly say how big it should really be. See the comparison here when I combined two sketches from the patent. The size of the body is the same but cranks themselves have way different length. So it is pretty difficult how large the gearbox will be. Let’s make it smaller and let’s have a look at the different positions the gearbox can have and why they wouldn’t really work.
If the gearbox has the main part of the body directed towards the rider, which would look pretty good, the range of adjustment for different rider heights would be very limited. It might be an option on bikes like Bacchetta or RANS where the bottom bracket is fixed directly to the mainframe and has no adjustments.
There is no way the body would be placed downwards. The front-wheel would hit it on many models with front suspension and it also looks pretty bad.
Another terribly looking position. Next to the ugly look is the fact that the chain can’t go between the cranks and the body so close to the crank axle.
So it seems that such a gearbox might be used on LWB recumbents like here n the RANS Phoenix. The situation on trikes would look the same as on SWB recumbent two-wheelers. However, the question remains. Why? What do you think?