I've been thinkin about the above post for a few days now & while it is largely correct there are some facts being distorted & some things that are just plain wrong.
It is important to understand there are way more than just two choices of either 180/55's & 190/50's on the market. We have 190/55 & 190/60 tires readily available now & other even larger sizes as well. It is also important to know that even though manufacturers may label their tires as 180mm they are usually not that exact size from model to model & especially from brand to brand.
The idea that the factories put a lot of time & testing into their suspension for their OEM tire fitment is kinda silly. First off the big 4 factories use a checklist in a boardroom to decide on the price they are willing to spend on the bikes suspension & work down from there based on whether they want to pay the extra dollars for damping adjustments, preload, USD etc... Stock suspension is crap. Only in the last couple years have we even started seeing OEM suspension pieces that were capable of setting sag for solo riding (new R6, 06 GSXR750 & the 07 600RR). Trust me the factories aren't fine tuning their suspension to their tire choices. They are following a formula for weight of the rider(s).
Second every manufacturer has at least 2 different fitments of OEM tires both with their own unique characteristics, but the suspension DOES not change.
BTW the OEM fitment versions of DOT street tires are usually heavier & more sluggish for turn-in & more expensive than the true aftermarket variant of that same tire.
More HP means more tire
Why? The vast majority of the street bikes on the road aren't using the OEM tires to their potential so why do we need to go bigger again? This seems like more of a personal opinion than any type of fact. Back in the day a lot of the British race teams running the 900RR/Fireblade which is so closely based on this 919 swingarm actually dropped to a 170 tire to aid in handling even though their race motors were putting out 40-50 more hp than the road going version of the bike.
With that said, here are some specifics.
In order to get the correct tire profile, the recommended street tire size for 5.5 inch rims specified by the tire manufacturers is 180/55 and for 6.0 inch rims it's 190/50.
You do realize that the manufacturers are now installing 190/55 tires on 6" rims right? That kinda blows your entire statement right out of the water. Furthermore for years the only race tires available for the 6" rims were 180/55's so that doubles the strikes against your claim instantly. Are you really wrong, not really, it was always taken as fact that this was the only suitable sizes for specific size rims when in truth there are way more ways to skin that cat. It's kinda like the guys that think they are supposed to run maximum pressures of 42psi in the rear & 36psi in the front tire ALL THE TIME because the manufacturer said so when in truth moderately lower tire pressures give the bike a better ride with more compliance allowing the sidewall to work as part of the suspension & more available grip from the tires from not only a better heat range, but a larger contact patch as well.
More importantly though, racers are now mounting 190/55's & 190/60's on 5.5" 600cc rims & are consistently dropping their lap times 1-2 seconds over the same compound 180/55's. This speaks volumes about the potential of the higher profile tires.
Back to reality & in direct regards to the 919 I can pretty much assure you that a 180/55 tire will do everything you could ever ask from it and seeing as how the adjustment of the 919 suspension is so limited anyway, it is the best overall choice for tire size requiring the least amount of compromise or fiddling with the geometry.