For the record, A LOT more sport/sport-touring bikes have the 180/55 size than 190/50: most 600s (highest sellers), most BMWs, most Ducatis, VFRs, FJRs, etc. Size 180/55 is considered the best compromise. A 190/50 tire turns in slower indeed, but powerful machines benefit from the bigger contact patch... or looks, like anything with less than 160 HP.
If the FJR has a 6" wheel indeed, a 190/50 is the correct tire size, and with its modest cornering clearance, the difference in feel should be minimal. And fit shouldn't be a problem at all.
By the way, a 190/50 tire on a 6"wheel is slightly smaller in diameter than a 180/55 on a 5.5" wheel, but both on a 6" wheel are probably identical since a 180 would be stretched. Normally, a 190/50 tire would make your speedo 1.3% more optimistic. And the difference in diameter is 1/3", so your ride height change would be half that; not a lot, but some on an already limited cornering clearance (at least for aggressive riders).
I'm going to check my wheel tomorrow, because I'd be extremely surprised to see a 6" wheel with a 180 tire; not only because it's the wrong size, but because it's more expensive than a 5.5 incher. Take care.
JC
