If you live anywhere with hills, you might find yourself short of gears. I don't think that evev extreme wide-ratio cassettes e.g. 11-50 T can match the range of a multiple-chainwheel setup - our Orbit Velocity has something like a six-fold range from a 3 x 10 setup.

I'd suggest slightly  larger timing-chain chanrings (40T?) both to reduce the risk of interference on the stoker's chainset and to reduce wear - larger rings will wear less. You may need a longer axle on the front to keep the timing chain in line.

You don't need to worry about using even the same sized chainrings for final drive and timing  for the stoker. We have the same sized rings on our tandem with no problem. I agree with the comments that you will probably run out of gears at the top end with a 1x setup. Also agree that larger timing chains will cause less wear to both rings and timing chain but I don't like the aesthetic of having the inner chainring of a pair larger than the outer. Depends upon your chain lines but you might be able to run the timing chain on the outside. Too small a gear range would be my main concern though.

Hi Matthew

We use a r/h timing chain on a highly modified, non-electric, Ecosmo folding tandem.

to achieve the range of gears, as referred above discussion, the mechanic recommended and then built a wheel with a Sturmey Archer 3 speed hub gear that can take an 8 speed cassette - and the model that also has a disc brake option which became the 3rd, drag, brake:  https://www.sturmey-archer.com/en/products/detail/cs-rk3-black

there are other options:  https://www.sturmey-archer.com/en/products/rear-hubs

With 20" wheels we have the hub gear combined with an 8 speed 11-40 cassette (in spite of Sturmey stating max 34T) and a 40T drive chainring. The Sturmey Archer hub gearing is 75%/100%/133% so is therefore equivalent to a 30-40-53 triple chainset. This combination produces a gear range of 15" to 97".

If you have 700 or 26" wheels, you may want a smaller chainring (a 32T ring could work well on 700 wheels - a range of 16" to 104").

The timing chainrings are 36T - on the outside at the stoker end. There is no interference with the drive chain.

Note also that the Sturmey Archer gear works with a standard 3 gear shifter, the same as one would use for a triple chainset.

BTW The 40T chain ring is an MTB square tooth 'narrow wide' alternating which alleviates the problem we had of the chain occasionally coming off of a regular chainring when changing (the derailleur) gear. It’s a 40T one of these: https://www.amazon.co.uk/gp/product/B08SVN59M2

All this might be more expense (and detail) when you’re might be wanting to save money on new cranks, but any way, ‘Good luck’!

Rob

Thank you for the thoughts, i am aware of losing some gears. However our tandem is predominantly used offroad & offroad touring so losing some high gears is ok - we just need the climbing gears still!

I think i will borrow parts from our mountainbikes and try it for a bit before committing.

FYI middleburn have told me they will no longer be producing 165mm tandem cranks or triple chainring spiders as there is no demand..... 

I recently converted my Co-motion speedster to a single ring option.

11-50 SRAM NX cassette - compatible with my existing freehub;  X01 eagle derailleur and chain; Microshift 12 speed SRAM bar end shifter.  Timing chainrings are 36 tooth and drive chainring is 48 presently but would be swapped out for something smaller for touring purposes.

This setup allows use of standard double road cranks - same sided timing chain and drive chainline is perfect.

I have run straight through drive to a 2 x 11 gear set for quite a few years now with no issues.  I use Spa cycles chainsets (cheap but sensible quality square taper) but have recently put new TA zephyr chainrings on.  These appear to give slightly more clearance between the timing chain and the drive chain.

I run 40 t timing rings with 46 & 34 drive rings.

having run 1 x 11 on a couple of solos I would echo the comments that you will struggle with range on a tandem.