My two-pennorth.. Because of the greater radius of the 190/55, I reckon you'd have more area in contact with the track/road - but less 'ground pressure' per sq mm because the bike's weight is more widely spread. (so on a wet/slippery surface you'd actually have less grip).
I could well be wrong though! One for Shazzam I think..
My 996SPS came with a 5.5"/190 rear setup which was changed to a 180 for all the "advertised" advantages. I then changed to mags and had a 6" rear but maintained a 180 tyre.
I've now got a 190 (D208RR) for Catalunya in October, having been convinced by Dunlops Sales Manager that the benefits are noticeable.
Having just bought a bike with what looks like a 6in mag rear, fitted with 180 (BT0012ss (?))...why does the tyre in general look wider and flatter than my 748 fitted with standard rear wheel and a 180 (pirelli diablo)?
Does the slightly wider wheel flatten the profile of the 180 tyre, or is the difference I can visually see due to the diference in tyre profiles from make to make?
pretty much answered your own question. it should have a 190 on if its a 6inch rim, the profile (as you correctly noticed) will be flatter as the tyre is being widened out. pop a 190/55 on and it should turn in better.
Well, thats what I thought...but then why do people stick a 180 tyre on a 6 inch rim to quicken the steering, if, as you suggest, it flattens out due to the wider rim???