Yeah my girlfriend is your wife's size, 5 ' 1" & 100 lbs. And she tells my on long rides her pelvic area get really sore but to the tiny, uncomfortable so called seat back there.Holy crap that looks sweet Slo. Does that just suction over the gas cap or does it bolt on. What's the link on that one? It is dissappointing that the Ninja 636 only comes with a little strap on the front of the seta by the passengers crotch area so there is not a full grab bar like I had on my SV650 which would have been a better ride for my wife and more upright.
I actually on my way home yesterday saw 2 separate Ninja 636 (new style and old style) both on Hampden at different times. Both had a male driver and a female passanger. I watched how each passanger was hanging on and both seemes to have lots of space between the rider's back and the passenger's chest and were barely gripping the side ribs of the driver. I told my wife about this so she would hopefully see that she doesnt have to bear hug me or grip me like a heavy backpack on my back. I think the driver blocks a good amount of air from the passanger that would otherwise pull them back. She did mention that when we got onto the E470 that she felt like her helmet was starting to lift so she was trying to tuck down to avoid that and thus pushing me down as well. The Ninja 636 is pretty raked and has little to no windshield curve to deflect air, anyone with one of these 636 has probably seen how it deflects hardly anything even for the rider, whereas the windshield on my SV650 it more upright and pushes it over the rider's head. SO this is for sure not the best bike for moving air over the passenger's head.
The idea of trying this again with her on another bike would probably be the best on something more upright. Harley riders don't even really need to hang on when they have a backrest, but the raking of the 636 and the small seat with no grab bar makes it pretty impractical for taking a passanger (as does the undertail exhaust that heats up their ass) I think the 636 is more of a race bike than most bikes that would be better suited for carrying passangers.