Looking at the pictures at the top of the post i'd say you can fit what the hell you like its making it work that will be the challenge.

Surely a bobber will look sweet on some spoked rims with the rear jacked out for a 6 inch rim (180 section tyre) and a real skinny 90 on the front, Its making it work that would be the challenge.

A stepped sprocket or maybe an intermediate shaft extension with an outrigger bearing would also let you have the really fat back end by spacing the final drive further out, or cheat and shift the motor over a touch.

Finding a suitable hub shouldnt be all that hard, look at some of the harley wheels should give you some options. It will handle corners crap but then thats not what a bobber is for is it?

For what it's worth, I have a 120/90 rear tire on my stock xs400 special rim (cast, not spoke). It's exactly 5" wide ... any wider and I would have rubbing issues with the chain and swingarm.

cool, btw Coker told me the 3.5 x 18" to them that my xs400 manual recommends in their system = 350-18...

http://store.cokertire.com/350-18-firestone-deluxe-champion-blackwall-tire.html

hehe, might be tempted to buy one next season.

I have rubbing issues, and the wife thinks its disgusting!!!

Well, you and me both drewps! But I don't have a wife to complain about it, so I think I'm good to go!