Bicycle Mechanics - Putting bigger rings on mountain crank

I have a mountain bike I want to use for more commuting. What issues will I have with putting bigger rings on it? Will I have to change out the front derailleur? What else do I need to consider?

Any input is appreciated.

You might need a new derailleur, but probably you'll just need to move it up a bit. Your main concern is going to be chainring to chainstay clearance. 48T is usually a pretty good big ring on a commuter mtb.

First, does your crank have bolted on chainrings? Second, do you have any particular reason for wanting to stick with the same crankarms?

I ask those questions because chainrings are generally not very cheap. To replace all three chainrings, or even just the two largest rings, on a medium to low end crank will probably cost you as much as buying a whole new crank. If the bike is low end, you can get VERY cheap 48/38/28 cranksets which are great for commuting (in my opinion of course).

This is nothing special but it'll get the job done:
http://www.universalcycles.com/shopping/product_details.php?id=16141&category=2637

This is about as cheap as it gets:
http://www.niagaracycle.com/product_info.php?products_id=6611

Here's something nicer with slightly smaller rings:
http://www.speedgoat.com/product.asp?part=133346&cat=32&brand=1004

Do note that you may need a new bottom bracket depending on which crankset you go with. The above are all square taper so if you have a different interface and don't want to swap, you'll need to find something else. Your current front derailler should have no trouble with a 48 tooth big ring. If you wanted to go with a 50 or 52, then you might want to consider a road front derailler though that brings it's own set a of issues, and for that reason I'd recommend sticking with a 48. A 48/11 combo is bigger than a 52/12 (common road bike top gear) anyway.

I have a mountain bike I want to use for more commuting. What issues will I have with putting bigger rings on it?

Why do you want bigger rings? Unless you're spinning out in your current high gear there's really not much point in the swap, and commuting speeds are rarely high enough for that to happen.

Sheldon Brown has a nice gear calculator that'll give you top speeds at various ratios and cadences, check it out.

If you haven't got a commute that's out of the ordinary you'd probably benefit more from going to a road cassette than messing about with your rings.

+1 Change the cassette, cheaper option.