I know a guy selling a barely used Mez4 front tire for like 50$. I was just wondering how the handling would be if this front tire is 120/60/ZR17 and my back metzler is 140/70/17. That would mean it just turns quicker in the front right?

 

it will turn quicker because the side profile is lower. but because the tire is going on a narrow rim, it will be kind of pinched causing the center of the tire to become higher. it has been my experience that the bike will turn quicker or drop into turns but the downside is that it may cause horrible side to side transition or muscling the bike back over to make the next turn. i've also noticed that at high speeds, the front gets unstable and heavy. you can put the tire on the rim but you do so at the risk of losing other handling aspects for quicker turn-in.

 

+1.......what he said. ^