preventec47

Since in this setup there is never any shifting taking place, in theory this is like a fixie or single gear bike or like BMX maybe.

I am wondering because if a chain does not have to shift, it might be made and shaped different to make it harder for the chain to come off
of the sprocket instead of being designed to come off easily when shifting.

I am in the process of getting a new timing chain for my 18 year old tandem bike and am not exactly sure what is the best size and type chain to get
for the bike. Of course I can see that the existing sprockets might influence the size of the chain but I dont know exactly what to look at to determine
what the sprocket wants.

aggiegrads

You can measure the sprockets to see if there is already a 1/8’ chain(the sprockets should be about 1/8” or 3.175mm wide. If it is thinner than 1/8”, any 3/32” single speed chain will work.

JohnDThompson 

FWIW, my Gitane tandem came from the factory with a 1/8" timing chain, but 3/32" rings.

Eggman84

Most timing chains are longer than the packaged chains; it will take two standard chains one of which is shortened. Measure the length you need and go to a LBS that has chain on a roll and can sell you the length you need. Better yet, call ahead to find out if they sell chain that way, then take yours to the LBS so you can get exactly what you need Single speed chain (designed for 1/8" sprockets) will work on any setup, but the narrow multi-speed chain may not work if the sprockets are 1/8". As to the chain staying on the sprockets, that is handled by proper tension; there should be some way to tension timing chains.

sch

Timing chains last 3-5x as long as the derailler chain on a tandem. It does not matter what kind of chain you
use. 5-6spd chains are fine but 8-9spd are also fine as are 10 or 11 spd chains. The current timing chainwheels
on the bike are likely 3/32 and will be compatible with any chain from 5-11 spd. Single speed chains could also
be used but connectors are a bit sparse as they are mostly connected by driving pins in and out. If by rare chance
you do have 1/8" timing rings then you will need to use a 1/8" chain. Your tandem will have an eccentric in the
front bottom bracket that rotates to adjust tension.

conspiratemus1

This might be more theoretical than real, but...
When the two of you are pedaling hard, the keel tube bows away from the two timing rings and the two bottom bracket spindles are longer parallel horizontally. (You can see this in photos of tandems at speed where the bottom run of chain becomes slack as the drive-side ends of the spindles are brought closer together.). This causes the two timing rings to be no longer parallel vertically. The timing chain must be able to follow this slight angulation without derailing. It makes sense therefore to use a derailer-type chain instead of a single-speed chain for the timing chain. Nothing is gained by using a single-speed chain for this application as timing chains last a long time in any case.

preventec47

I measured my timing teeth on the shimano timing gears and got .083 which is less than 3/32. Thinking the ebike chains might be a little stronger than regular bike chains this is what I ordered. TWO of the 8 speed version ebike chains with EPT. https://www.kmcchain.com/en/product/...t-8-speed-copy of these chains as I need to create a 148 link chain for the timing function on the tandem. I also feel the anti rust treatment might also result in some increased longevity with respect to chain stretching.
This is a deraiuler chain as opposed to a single speed chain as I was convinced by the previous message about deraileur chains less likely to come off the sprocket.
https://www.kmcchain.com/en/product/...t-8-speed-copy

product link https://www.kmcchain.com/en/product/...t-8-speed-copy

79pmooney

Warning, this post is completely irrelevant but kinda fun. I've ridden more than a few organized rides on my fix gear (1/8 chain and sprockets). Flip-flop wheel and often carry a third (tiny) cog and chainwhip. (You can see both on my logo.)

When I encounter tandems and can ride side-by-side with them (that's not often!) I point out that my bike and rider are a half tandem bike and team. My bike is the front wheel and cockpit of the tandem and stoker seat tube back. None of all that derailleurs, cogs. Just a timing chain. Now when it comes to the team, my half team is captain waist up, stoker waist down. Captain picks the route and line on the road, chooses the gear (this captain is a little odd - he only shifts at a standstill and absolutely refuses to coast). Stoke does all the work.

Tandem captains are usually not impressed by my analogy but the stokers get it.

Darth Lefty 

Some newer tandems have been using NW chain rings with matching 11 speed chain.

Presumably all the chain efficiency and wear testing and chain price per mile articles we keep sharing, also apply here.