two sets of wheels
 

I have two sets of wheels on an old Hard Rock mountain bike. Since I have two different cassettes, should I have two different chains?

Thanks!

Depends on the cassette, derailleur, and number of front chainrings.

To expand, chain length should be the same or close so one factor that needs to be considered is the largest cog on both cassettes assuming you're using the same large chain ring. Also, the rear derailleur should be able to handle both cassette ranges.

I'm also running two wheelsets on one of my bikes. One with a set of knobbies with a 11-32 cassette and slicks mounted on another with an 11-28 cassette for road duty. I started with new cassettes and chain (sized for the 11-32) and swap wheels evenly as to even out wear on both wheels. If you wanted to take it further and maximize the life of the chain/cassette, get a matched chain for each cassette/wheelset but that would be a slightly labor intensive.