I have read Sheldon Brown's writeup on chain length (1 link beyond meeting around the biggest ring/cog), but have a question he didn't answer. What if I want to swap cassettes? How can I acheive a functional compromise? For example, I have a 48t large ring. I have a cassette with a 25 large cog and I have a cassette with a 32t large cog. Is there any way I can size the chain so I can use either cassette without modifying the length of the chain?