My wife adores her 3-speed Torker Tristar tricycle, and despite my urging, she will not be swayed to try any two-wheeled contraption. She would, however, like to have a broader range of gears to choose from when tackling the hills of Austin with me. To that end, I'm investigating an upgrade to her trike's Sturmey-Archer TS-RC3 gearbox (http://www.sturmey-archer.com/produc.../id/41/specs/1). It is mounted between the crank and the rear wheels, in a horizontal dropout 131mm wide, connected to the crank in the usual manner, and outputting to the rear axle via a ring-shaped gear attached to the drive-side spoke holes.
It looks like a Shimano Nexus SG-7C18 7-speed with coaster brake would just fit in the space (reports of its OLD vary from 130mm to 132mm). I don't know if (and don't think that) the spoke flange gear from the current hub would fit on the new one. Where could I find such a gear, or how would I go about having one fabricated?