INstalling a smaller crankset.
 

Currently I run a 52-42-30 triple on my roadbike, 175mm arm length.

I need to replace it. The crank arm is cracked.

I'm thinking of replacing it with this

http://www.amazon.com/Shimano-M191-1...9559848&sr=8-1

shimano m191, primarily b/c it's 48t and it has a chainguard.

Anything to look out for? How about front derailleur adjustment? is this doable?

You'll need to lower your front derailer by about 8mm for best shifting. On some bikes a with bracket mount (aka "braze-on") front derailer, the bracket does not allow the derailer to be lowered that much. If you have a clamp-on front derailer, there should be no problem.

You will likely also need a new bottom bracket unless your current crank happens to use the exact same type and axle length.

that's what i thought.

I feel I must say, that looks like a rather cheap (quality) crank, and I would probably steer you some other direction. You can get a forged 110/74 triple on Ebay for about the same price, and it would be a much better buy in my mind.

i actually have a truvativ sitting on my desk right now...except I realized that it's isis :(

the chainguard is a big appeal to me, as I regularly get my right leg dirty with my bike.

Try cleaning your chain

beyond that though, like I"ll get my shoelaces tied up in the crank, I've actually scratched my right leg -- there are scars, from the crank.

Shoelaces and bicycles don't go together well.

Are you aware this crank had non replaceable chainrings?

As far as keeping your leg clean and undamaged . . . yes. . . simply wipe the chain after each ride. Shoelaces? No problem. I wear shoes that have very long shoelaces. . . I double tie them, and tuck the leftover underneath the forefoot laces so they don't flop around.

what? I'd replace the whole crank obv.

update: I've decided to stay with the truvativ elita. I'll get around to installing it when I receive the BB. Changing the crankset to something like that would have permanently changed the identity of the bike.