I’m considering an upgrade for our tandem from 3*10 to 2*11. We’re currently runing 3*10 but the shifting on the front triple is not brilliant.

Realistically, how low can we get the gearing on 2*11? The current triple is 26-36-48, with an 11-36 cassette. If I went to a double setup, the standard double tandem chainset from tandems.co.uk is either 50-34 or 46-30. Going for 46-30 should be fine, we rarely need to use the very top gear. but gives us 4 teeth more on the lower chainring – significantly harder, and we use low gears a LOT more than high gears

Our current bottom gear of 26/36 on 700C 35mm works out at 19.62 gear inches. To get the same with a 30t inner we’d need a 42 tooth cassette. Is that acheivable with standard road shifters / derailleurs? Will it work with Di2? or SRAM eTap? With the latter, is it necessary to use an SRAM cassette? The current cassette is shimano fitting.

I’ve 30/46 fsa crankset and 11-40t cassette working with an ultegra 6800 rd without having to use a wolf tooth road link or similar.

No idea about Di2 or SRAM wireless

Sub in a grx rear derailleur?

I have GRX 2×11 on my winter/audax bike, with a 48/31 chainset and 11-34 cassette.

Think you can get a smaller chainsaw* as an option
*chainset, damn autocorrect

Chainset need to be tandem specific – either crossover, or something that will allow me to run timing chain on the drive side. Interesting that you have such a big jump on your chainset though, I don’t think I’ve seen anything quite so big before. As it were.

Anyway having done a bit of checking, a GRX derailleur will do 42t rear

https://bike.shimano.com/en-EU/product/component/grx-11-speed/RD-RX812.html

But XT will go up to 50T.

https://bike.shimano.com/en-EU/product/component/deore-xt-m8130/RD-M8130-SGS.html

Will an XT derailleur work with e.g. GRX or 105 2*11 spd shifters?

Unless things have changed recently, you can mix road and MTB Di2, so you could use an XT Di2 mech on a 2x set up with an 11-42 cassette and be within Shimano’s recommendations, whereas GRX either lacks cassette range compatibility (RD-RX812) or lacks capacity (RD-RX817).

Technically, the XT option also lacks the total capacity you’d need for 30/46 11-42, but Di2 will prevent running in smallest sprocket combos that would lack sufficient chain tension.

While I’d love to get a Di2 setup, it isn;t cheap, so if I could get this working with just standard cables then that would be preferable

You can mix Shimano road STIs and MTB rear mechs if you add a Wolftooth Tanpan 11.

Got one on a bike with GRX STIs and an XTR 11 spd rear mech – works well.

I’ve 30/46 fsa crankset and 11-40t cassette working with an ultegra 6800 rd without having to use a wolf tooth road link or similar.

I’d look into this, with the 46-30 crankset.

You’ll lose half a gear off the bottom realistically with 30×40, and I agree that the top end loss won’t be a problem, 46×11 is quite enough!

You could end up spending a lot on di2, not sure it’d be worth it for this.

Sorry, I know nothing about tandems and very little about road groupsets, but if 3×10 gives you the gears you want, perhaps a cheaper/simpler option might be to sort out the front shifting. What’s causing problems.

3×10 48, 36, 26 with and 11-36 cassette is standard (and current) Shimano Trekking fare (although it’s fairly out of date kit). The mechs. are specifically designed to work with the 48, 36, 26 triples but the problem is that they’re MTB groupsets; could you run one with a road shifter?

Sorry if I’m being stupid.

perhaps a cheaper/simpler option might be to sort out the front shifting. What’s causing problems.

Triples are always hard to adjust in general – with this particular setup (Tiagra 4703), I often end up having to overshift to move up a ring (sometime it just won’t go into big ring), or struggle becuase it won’t dropdown to granny. More, the left hand (fromt) STI unit has now been replaced TWICE under warranty. It seems that pulling the cable put so much pressure on the shifter that the body actually collapses. The new shifter was only fitted in May and the shifting is already going to pot. We’ve ridden about 500km on it since the new shifter was fitted.

I’m running 48/32 and 11/40 on latest gen 105 11 Speed (gs) on one boik and 50/34 11/40 105 5800gs c/w goatlink on another. I can get all combos and no floppy chain with each, both mechanical obv.

It can depend on your particular geo and derailleur hanger so unfortunately, some experimentation may be required.