No, it is easy to move that. A 12t is just fine, but to tighten up the chain, you need to adjust the housing, it is so simple. Between the sprox hub and the brake hub, there are 2 nuts, one it on the top and one is lower, loosen them both. Then, there are 2 bolts, with a nut, loosen those, and the whole housing will adjust the chain for you, just pull back. Good Luck.