Sheldon Brown had this to say: "Although "road triple" cranksets commonly come with a 30 tooth small chainring, it is very easy to replace this with something more reasonable, such as a 26 or even a 24. If you go with a 24, you would also be well advised to add a chain deflector such as the 3rd Eye Chain Watcher or the N-Gear Jump Stop.
Using one of these devices allows you to set the low-gear limit stop loose enough to provde positive downshifting, without the risk of the chain overshooting and falling off inward.
This is by far the cheapest and best way to lower the gearing of a stock bike with a road triple crankset.
This will exceed the official "capacity" of your derailers, but generally works fine with original stock "road" derailers as long as you don't make a habit of abusing the small chainring by running it with the smaller rear sprockets."