The rim on the bike is designed to run a 180. installing a 190 will slow the steering down and you're effectivley pinching the beads in to fit it to a smaller rim. I have also read at full lean the contact patch is affected( not in a good way).
A 190 on a 5.5" rim will slow steering (as previously stated), and provide a smaller contact patch at any given lean angle. Basically it would make things worse for the sake of dubious fashion... I've run 180's on my R1 with nearly twice the rwhp as a VFR, with no need for more grip that a 190 (on a 6" rim) might offer, except perhaps for track days and/or actual racing. Stick with a 180 on a 5.5" rim - end of discussion. I currently run a 170 on a 5" rim on my '94 VFR, and it works just fine, and I tend to hassle kids half my age with twice the horsepower, 100lbs less bike, with 6" rims, 190 tires, mag wheels, and all sorts of fancy stuff. Just ride the bike the way it was designed. You don't need more grip until you need more grip! ... and if you need more grip than a 170 or 180 on the street, take it to the track...
I wouldn't do it, when it comes to size applicability specifications ask your M.O.M. My FZ1 is a 190 rear stock, I can't even use the full width of the tire before I start scraping hard parts, but really during street riding you shouldn't be at your bike's absolute limit, always leave room for the unexpected. Asides from the contact patch issues brought up by others, I would think having a tire bulging off the wheel would cause severe stability issues in turns and add useless unsprung weight. edit: Oh and I've never broke the rear wheel loose just rolling on through a turn in any of my bikes, paint lines, tar snakes and dirt have. Right now I'm just running a Pilot Road II sport-touring tire and it performs great for the type of riding I do.
