hi all i have a triple chainring on my road bike with a five hole spider, to save weight i would like switch to a two chainring setup. i would like to do this by just changing the rings keeping my cranks, is there any problems involved with doing this ?

If you use index shifting on your front derailer, there may be problems there.

Chain rings don't really weigh that much, so I doubt you'll notice the weight loss, especially if you're ditching the little ring.

will currently my rings are steel, i was going to switch to alum..

Any particular reason you're keeping your cranks? I'd rather swap out a crankset than pull three chainrings and replace two, anyday.

Which shifter, front derailer and crank are you using?

In theory, no. However, doing it this way may not be possible if you can't lock out the granny chainring position with the front derailleur's limit screws. In fact, that's the easy way to see if it will work- just adjust the front derailleur so that it won't shift to the inner chainring. Then try some quick shifts from the big to the middle ring. If the chain drops to the inner at any time, the conversion won't work- you'll drop the chain onto the bottom bracket shell sometime and end up spinning the pedals.

If the chain doesn't drop all the way -ever- then go ahead and remove the granny ring. I really doubt you'll notice the difference, though. It's not that much extra weight, particularly on a bike that started out with steel chainrings.

i am just trying to save money, my cranks are truvitiv and they are alum. it is a flat bar road bike so it has the trigger shifters from shimano.

i am just trying to cut some more weight cheaply. i have got the bike down to a little over 22 lbs, i would like to get it to 20. i already have a carbon fork and lighter brakes, after xmass i will have some lighter wheels to put on it, so i should be able to get it close to my goal.

The indexing will not change, your shifters will still shift the right amount. The first step as noted is to get the limit screws adjusted properly. You may need to install a longer screw.

The disadvantage is that you will not get the improved chain line that you would have gotten with a double and you will still be using a triple front derailleur which may have a cage wider than what you want for this application. The mention above of the chain falling off the middle and onto the BB shell would be an example of the proper derailleur cage not being available to do its job.

How much money will be saved by the absence of an inexpensive chain ring?

Guarantee you can loose the weight of the granny ring and more via your diet. Don't get hung up on weight of the bike.