Hi Kevin,
I can see the discussion went not so far on the subject
Have you found anywhere else the satisfactory answer to yur quest? I mean not the one like: "It's recommended so and so rim width for 160 tyre" or "Why you want to change something what was designed to be like it is, are you wiser than the bike designers?" or "You want wide tyre, why not go for Hammer instead". I'm sick already with some forums and their advisors.
I also do plan 160 on the rear first change, however it's still some 3 years to go... What I know, the High Ball in 2012-13 came with 150 rear on same 3.5" rim, I hope 160 shall be on the upper limit for the rim, but better to find one who tried. 150 is still not wide enough:grin
BTW there is a lot more 'bout the tyres in HB section of the forum. Looks like HB owners are far more eager in customizing, cutting and cropping their rides. I know, coz last winter I read most of the topics over there while still orientated on buying the HB. Myself not so old yet, but always had in my head the only cruise bike picture with "real", shining, spoked wheels. On the other hand, mature enough to leave behind all the shining, chrome leaking armature... Then I saw the High Ball, the picturesque of my imaginations of perfect cruiser. HB attracted me to new Victory line, which I started exploring, and when I saw the Gunner's wheels, I was sold. Cast aluminium, bare-metal-edged spokes... Even my wife didn't tell it looked like from museum:wink
Back to the tyres, I saw a couple HiBalls with 200 rear. With no modifications to the swingarm and even original rear fender. Of course on rim wide enough. I do not want to get rid of stock rim, but If 200 fits, I am sure 160 will easily find enough clearance for free rolling.
Some say the high profile tyres are less vulnerable to rim width. In other words you can put (reasonably) wider tire on narrow rim and it won't loose the shape as easily as the low-profile one. It sounds logically, there were even cross section sketches for the two cases in one of sport bikes' forums.
As for today, I'm nearly sure I will go for 160 in a couple of years. I assume 10mm (less than half of inch) extra rubber each side will not be too much for the stock rims. But I will know for sure only when I try... unless I met one, who tried already and failed. Maybe you wanna be the first?...