I might be able to actually help answer this question (or at least provide some factual evidence) for anyone considering the pro's & con's of changing Rr. Tire sizes.
Got this idea from recent DMT tire comparison vid. I used my contour gauge that I normally use for flooring installs. I'll Attach the image.
So far, I think the results are pretty interesting.
1st off. Yes I upgraded to Q3+'s right after getting the Bike. Couldn't find a 180 @ the time, so I went w a 190/55/17. I did a bunch of research & w our bike & tire rim a 190/55 is fine from a safety stand-point & once mounted, although the 190 is slightly wider, the bigger difference is actually the steeper profile of the 190 tire on the 5.5" rim. I really wanted the Q3+'s & was actually interested in trying it out.
Aside from the obvious improvements the higher performance tires & stickier compounds would make, once scrubbed in I immediately noticed a significant improvement in steering response, specifically re: tip-in & overall flickability from the steeper profile on the rea w no discernable drawbacks initially, but over time I did notice some definite tradeoffs, so ultimately I'm not sure I'd do it again. Fortunately, I should know for sure soon, since I just received the new 180/55 rear I ordered and am having it installed in the morning. I'm anxious to get it on and compare it to the performance of the 190.
I went w a Q3+ again since I was really happy/ impressed w the performance of the tires overall & they wear at a rate of about a 1/2 ratio, Rr/ Fr. From day 1, the Q3+'s were a night & day difference from the stock tires! That said next time around I may try something else out just for the knowledge & experience/ for comparison sake. I'm curious to see how different brands really compare in terms of performance & longevity.
Speaking of... My current 190 is wore down to the wear bar indicators after about 3K miles of hard riding inc. 1 track day. Which isn't terrible, but I was hoping for the closer to 4-5K that many other riders w similar bikes claim to get out of their Q3+ Rrs or even the 6-8K people claim to get w some other brands of hi-performance tires like Michelins etc.
The only potential downsides I've noticed from the 190 vs 180 are...
1. They wore down wayyy faster in the very center than they did on the sides or even the full crown of the tire, the wear accelerated w mileage & ultimately resulted in a very flattened center-profile. This drawback became more & more noticeable in the bikes handling-feel & I'm pretty sure it actually led to accelerated tire wear & decreased straight-line traction (pretty much always).
2. At times my Rr. tire would spin unexpectedly in 2nd gear, particularly when doing clutch ups or even just doing power wheelies if it was less than 50-60 Degrees out. This is w tires fully warmed up and on good pavement @ 30-40mph. I won't know for sure if this was a result of the larger tire size until the this fall when temps come down again & the 180 is broken in, but it did seem very unusual for such a sticky compound tire, especially when running pressures as low as 30-32psi cold.
All this is to say that given the extra cost, accelerated wear and diminishing returns in profile steepness over the life of the tire & potentially reduced upright traction. I don't think there are any logical advantages to using a 190 vs 180 w a 5.5" rim. Especially when u can see from the pic, that there is barely a perceptible difference in appearance re: tire width "Cool Factor".
Btw, if anyones looking. I did find some great deals on good Continental & Michelin tires on sale this week. Lmk if u want the links or any other info etc✌