Chain replacement
 

How many miles are you fellow tandem riders getting on your chains before you have to replace them?

It varies from team to team depending on a variety of things, including the team's weight/power output, riding terrain, e.g., climbing 500 hilly miles are a lot tougher on a chain than 500 flat miles, and of course attention to maintenance/lubrication.

Your best bet for getting the most life from your chains without putting unnecessary wear and tear on your cassette cogs and chain rings is to routinely check your chain for wear. You can use a 12" ruler or you can buy a "chain checker" tool from Park Tools to do the checks. The more you ride the better idea you'll have about how often you'll need to replace your drive and timing chain.

You can read more about chain maintenance here:
http://www.sheldonbrown.com/chains.html

I use a "scythe" to measure my chain wear. It is the only name appearing on it and it looks just like the name. One end hooks into a link and the other end has waht must be a changing radius with percentages marked on it ie at 100% you junk the chain. It is small and compact and well made. We normally get about 2500 km on a chain. Most of the time I manage to junk the chain by getting it magled on the chain wheel. I have now fabricated a guard ot of plastic to stop the chain form slipping into the crank.