need help with chainring change
 

I have a shimano xt (I think about 1998) on my touring bike and a 22-32-42 triple. I never use the 22 and I would like some more teeth for the middle and big ring. Can I change this set up without changing the derailleurs? And where would I find rings that work with the old xt? Thanks.

First, find the bolt diameter, and bolt count.
http://sheldonbrown.com/gloss_bo-z.html#bcd
I'm not sure if Nashbar or Perfomance have single rings, but loosescrews.com does have chainrings. An LBS should be able to order some too.

One thing to watch for: I don't know what BCD's are on your crank, but you may not be able to fit the one you want, due to interference issues (between the bolts and the teeth). Also, the FD will most likely have to be moved upwards, so as to clear the big ring; and if you leave off the granny gear, you'll have to reset the lower limit screw. I'm not sure if you have to replace the derailer; I think it'll still work.

Ideally, you also want the curve of the FD cage to match the largest chainring. This isn't critical but if you stay with a triple you want it to be 'close'. FD's are cheap, though, so I'd just get the rings you want and try it. If the FD adjustment gives you trouble, swap it out.

My son's bike has a 22/32/42 as well. I kept asking him why he was always in the top gear and never shifted - now I know :rolleyes:

Yes, probably. I have a MTB with Deore LX 5-arm that was originally 22-32-42 and I swapped it to 22-32-46. My FD (also Deore LX I think) is meant for a big ring of 44T but it works fine on the 46T. Selection isn't very good for 5-arm and I think it's even worse for 4-arm. I got my rings (it was a set of 44/46) new on eBay.

As a general rule, front derailleurs intended for large chainrings will work adequately with smaller ones. For example the late '90's Trek 1220 came with a 26/36/46 RSX crank but an RX-100 front derailleur made for a 52T large ring and it shifted pretty well.

An fd made for a small outside ring will have too much curve to the cage to clear a large ring if mounted low and will have to be mounted too high to shift well.