sprocket choices...

[twangin4u]

I have 17/42t on an 18" wheel. Its time for a new chain and im contemplating changing up sprockets for the heck of it.  Im wondering if I do change and im not happy would adding a tooth or two be possible with the existing chain? Is there enough adjustment for it?

[fj-f3a]

The centre to centre distance of each link is 5/8" (16mm), therefore 5/16" of adjustment would be required for each additional tooth added or removed.

An 18/40 front/rear should be OK but an 18/38 may require a shorter chain.

I run an 18/38.

What is the circumference of the 18" tyre. An 18/40 or 18/42 may be a good choice.