I'm currently running Campag 8-speed on the tandem. 8-speed chains are still reliable. I'm thinking of going to 9-speed, but of course the chain would cost a lot more, and I'm not sure the extra cog would be that useful. No way would I run a 10-speed cassette and chain on a tandem; they even break on singles. This is bleeding-edge racing equipment. Our team weight is 320#, and I'm an ex-racer. A very smooth sub-300# team might be able to get away with 10 speeds, but even then I'd be careful any time I was out of the saddle...

(I guess running 10-speed chain on a tandem is sort of equivalent to running a single-bike carbon fork or similar critical component not certified for tandem use.)

With 8-speed, you can use cheap 8-speed chain, which has wider rivets and a lot more tolerance for the chain flexing across the cogs. The timing chain doesn't bend laterally at all, so it should last far longer and you can use the cheap Nashbar recumbent chain, or even 1/8" track chain, which is designed not to flex laterally.

I normally replace the drive chain on my bikes at between 3,000 and 4,000 km (I don't like wearing out the cogs). The timing chain can go twice that.

L.