If you build mono swing arm. The frame is not designed for one. You will have to weld gussets to strengthen the frame. A single sided shock like the BMW K1100rs would be much simpler. And still be able to move the right side exhaust pipe closer to the frame. Like many modern swing arms FJR1300 swing arm is very strong and light and will easily handle the stress. Also the rear master cylinder will get in the way of the wider swing arm and will have to be moved to the outside the frame. See one of my picks. I also have designs to change cable clutch to a hydraulic clutch and some pics of completed chain and shaft drive xs1100’s. If your interested I will dig them out. Hope this helps.
Thanks man, I'll take whatever pics you've got!
As for the gussets - I plan on chopping off the rear subframe anyway. My goal with the rear of the bike is to clean up that whole area. Hence why I don't love the factory shock mounting locations, it just looks too crowded and busy. I'm not afraid of the fab work - I own a few CNC machines for my day job (cabinet maker / woodworker) so I have an okay working relationship with several CADCAM options. Plan is to cut the rear subframe out, draw up some nice seat brackets and have a local guy laser them out for me with 1/4" steel or the like. I can add bracing wherever necessary. The new seat bracketing parts can also provide a new landing spot for upper suspension mounts.
Another goal, besides the aesthetics, is to hopefully be able to use a wider rear tire. However, I'm starting to think that just using the notch method on the factory shaft tube I maybe can squeak in a 140? Would rather a 180, but I think I could be happy with the 140 since I only really plan on this being a buzz around town kind of bike anyway.
In your opinion, do you think I could modify an R1 wheel to take the shaft drive? I have a machinist next door.
If I could get a bit of a wider tire on there, I'd keep the stock wheel. Then I'd be tempted to try to figure a way to keep two shocks, but to move the mounting locations to reduce the angle of the shocks so they don't attach up near the seat, but rather lower somewhere on the main frame. Again, I'd brace as necessary.
This guy on customfighters used his factory swingarm and it looks pretty good - won't let me DL the pics but here is the link - about 2/3 of the way down the first page:
xs1100 Fighter | Custom Fighters - Custom Streetfighter Motorcycle Forum
Sorry for the mental diarrhea.