The main difference between a 190/50 and a 190/55 motorcycle tire is the height of the tire as a percentage of its width.
The 190 on the tire refers to its width in millimeters, and the following number, in this case, 50 or 55, refers to the height of the tire as a percentage of its width.
A 190/50 rear tire will have a flatter profile, offering more grip at modest angles of lean but a slower steering response.
On the other hand, a 190/55 will have a more triangular profile, generally providing an improved contact patch at higher angles of lean, along with quicker turn-in.
Lowering the front of the motorcycle decreases ground clearance slightly at lean. The 55 series still has a sharper turn-in than the 50 series, but the difference is not as noticeable as when the bike is set up from the factory for a 50.
A flatter 50 would last longer and stay rounder for a lot of slabbing, but the 55 is generally preferred for its handling.
The 55 raises the rear more than the 50, making the bike flick/turn in quicker. The 55 usually costs a hair more than the same 50 tires.
Most who top out the bike prefer the 50 or the OEM 200/50 for stability. The 55 is usually better for rolling the tire over into corners. However, motorcycle tire profiles can be different even in the same exact size tires from different manufacturers.
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