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No mention of the friction in the driveshaft. Would there not be a twisting load on the shaft from the chainring pressing aginst it? The system needs a mechanism to move the rear driver back and forth. More friction.
davidual-
And presumably, the spacing between each gear on the back is different, and therefore the shifter must be specific to any one "cassette".
I think they also missed a trick with making it compatible with a normal freehub body. Surely one of the major advantages is that it is flat, and therefore the rear wheel can be more symmetric?
chiroshi
"DrivEn hits the magic 99% efficiency number at 380W of rider output"
So, pretty much the same as a single speed roller chain :)
Strictly speaking, their system only completely avoids sliding contact at the drive interface if the outer races of the rolling elements are conical, and the cone angle needs to be different for each different driven gear as the apex has always to be coincident with the axis of the driven gear.