190 refers to the rear tire width in mm's. A 190 is slightly wider than a 180. I'd say keep the 190. A 180 will give you quicker handling at the expense of some traction, you need traction more than handling on that bike. At least for now.
The explanation of the rest of the code:
190/50/ZR17
190 is tire width,
50 is aspect ratio at max lean
ZR is speed rating
17 is rim size.
__________________
Entia non sunt multiplicanda necessitatem
|