Join Date: May 2004
Location: Agua Dulce, CA
Bikes: Surly Crosscheck single/9 speed convertible, Novara Buzz beater
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Well, you can run nearly any crank you want. I mean it's possible to cobble all sorts of things together. The first thing to consider is how big, or small, a ring you need up front. That will tell you whether you need to consider a road or MTB crank. Generally, the smallest ring that will fit on a run-of-the-mill five bolt, 130 spaced road crank is 38 tooth, although some newer 'compact' road cranks run 36's.
If you're building an honest to goodness cross bike intended for racing off road you might need a smaller ring. If so, a mountain bike crank is in order. There are quite a few purpose built single speed MTB cranks, and you should be able to find a deal on one.
I ride my own Crosscheck mostly on the road, although I do sometimes stray down the ocassional dirt path. At the moment I'm running a 48 tooth road ring, on a FSA road cranks, mounted on a Bottom Bracket with a 113mm wide spindle. The MTB width BB allows the chain to line up with a Novatec single speed MTB hub with an 18 tooth cog. The nice thing about the Novatec is that like the much more expensive King SS hubs, it has cogs that slip on and off a cassette type holder instead of threading onto the hub. This system includes a spacer in addition to the lockring so you can adjust the chainline a bit. This is very helpful when you're putting together a frankenbike from spare parts.
You can also help the chainline by mounting the ring either inboard, or outboard on a road double. Of course if you'd like to run a bash ring outboard you need to get it right with the chainring inside.
The only other major thing to consider is the width of that bottom bracket spindle. Generally, if you're running a 135mm MTB hub in the rear you'll need a 113mm spindle. If you're running road hubs you'll need a 108 or thereabouts. I ebay'ed a 108 by mistake, but was able to adjust my cog in the rear to comensate. It worked out OK, although the narrower spindle did place my heels a little close to the chainstays.
Hope this helps. DanO