180 rear tire on a '07 R1

My question is pretty simple. I was wondering what's the problem (if there is one) if I put a 180 55 zr17 instead of a normal 190 ?? Because my girlfriend is racing and she's using pirell Supercorsa and she can give me her set of tire after avery race. So I can use it on the street. so there must be a difference in handling or something like that? thats what I would like to know :) thank you for your help

Won't be a problem. In fact, the bike will handle better, and you'll notice quicker turn-in.

+1 I've been running 180/55 on the R1 since I replaced the stock tires. Love the handling but I'd like more contact patch. I'm going to start using 190/55 for the track as soon as I use up my last couple of sets of 180/55's.

ok thx for your input! I'll use her supercorsa without a doubt. It's going to be cheaper to ride this season :)