[derstuka]

Mark, as long as you have clearance, you can put any tire you want on your rim, however, since it is a wider/larger tire, you may slow down your turn in. Putting a larger tire on a smaller rim (to restate what Dr. Taz stated prior) can affect the tires profile and performance. Whoops...I meant tyres...haha

It doesn't mean you are gonna go in the ditch, eat shit, or you bike will self explode, but your bike may handle better (quicker handling, turn in) with a smaller 170. If you do mainly city riding, if would not matter as much probably.