Chris Timm
Hans Christoph Timm

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The front and rear cranks on a tandem are connected via the timing chain (also called 'synch chain'). Like all bicycle parts, the chain and chainrings will wear out eventually. Stop and look at the timing rings (the chainrings connected by the timing chain) more closely before you replace them right away though: If you study them, you will notice that the teeth on the two timing rings wear on opposite sides. The captain's ring will wear on the leading edges of the teeth, while the stoker's will wear on the trailing edges. I can hear a lot of captains chuckle already, saying

WRONG! This has nothing to do with how hard either of you two is pedaling! The timing chain is transferring the captain's effort to the rear of the bike. To do this, the front chainring has to pull the timing chain (its upper half, to be exact), which in turn pulls the rear chainring. At the rear cranks, the stoker's input is added to the forward force supplied by the captain and transferred to the rear wheel via the drive chain.

The only possible scenario in which the timing rings could look any different would be if the captain would continuously try to backpedal. Then the stoker not only would have to propel the tandem, but also force the captain's legs forward. To do this, the stoker's chainring would pull the chain (its lower half this time), which would pull the captain's ring. This couple's timing rings would show wear opposite to what I mentioned above: The captain's ring would show wear on the trailing edges, while the stoker's would be worn on the leading edges. It is more likely that the stoker would have simply got off the bike and gone looking for a better captain long before the bike showed any wear, though.

Thus, should your timing rings look worn, simply swap front and rear rings, put on a new timing chain (because you will now be riding new timing rings), and ride on. This will double the life expectancy of your rings. There is no need to swap the rings back and forth several times - just wait until they are worn, swap them, and ride the same distance again until you have to buy new rings.

Remember that you'll need to readjust your timing chain as the new chain will shorter than the worn one.

Now what do I do if I have a triple or a quint?

A person asking this question probably doesn't own a triple or a quint. Otherwise they would have noticed that even bikes with an odd number of cranksets have an even number of timing rings - two for each timing chain.