A typical single front has the driver/stoker chain on the right, a triple usually has it on the left. An upgrade to triple might involve changes to front cranks as well as rear ones.

We have a triple on our basic Viking (with xf07 electric front), but I think that has front 48/38/28. We almost never use the top at the front.

We are changing the Viking to an even more basic electric Ecosmo. That is mainly because of the high crossbar on the Viking, not as high as many but getting awkward for me. The Ecosmo comes with 14/28 freewheel that gives an absurdly low (even for us) 50" high, 25" low. We are probably about to change to 11/32 freewheel (64" to 22") or 11/28.

This will give rather wide jumps but should be OK for our leisurely electric riding.A similar change for you with a larger front sprocket may give the range you need and a simpler change, but you may just not find it adequate.

Engineering on an 11 sprocket freewheel gives somewhat compromised engineering. I don't think that will be an issue for us, leisurely riding with the rear hub electrics taking most of the strain. It could be for people who put more power through their gears; there are some poor reviews because of that. Bearings for 11 cog is not an issue with cassette, but small sprocket wear could still be.

I've had a similar issue with our 90ies tandem that I bought secondhand, a classy steel frame with all Campagnolo, but a bit too highly geared for us. The main crank was a double with a bolted-on third inner ring for the timing chain, run on the right. That crank had only one ring of bolts, so the 42t timing ring was the smallest, barely smaller than the 46 of the lower gear. The campy ergo shifter that is installed does lift fine for 3 rings. The chainline of the old setup was slightly out to allow for the timing chain, but worked.

Moving the timing chain to the left was not a big issue, found 2nd hand Campy parts on ebay. Fortunately the eccentric front bottom bracket came free after some effort to adjust to the different length of the new timing chain. 

The campy triple that I found (needs to be campy as their square taper for the bb spindle is slightly different) sits much further out, the chainline now needs adjusting. Could possibly be done by screwing the right bb shell further in and flipping the asymmetric bb spindle around. Or by fitting a new bb with narrower spindle. Unfortunately, so far, the pin-hole bottom bracket refused to budge. With some destructive means it might move in the end, my local bike shop says.

Final piece for moving from double to triple: I'll need a longer cage for the rear 7/8 speed derailleur. For Campy, that appears to be an issue, all I can see are very expensive vintage parts from the US. Failing that, there are competing claims that for 7/8sp 'Shimergo' works fine, others say not really.

If your setup is Shimano, I think you should be able to get this to work. Good luck.

To give you an idea of a triple range, my Orbit tandem has a triple chainring set 26 / 36 / 48 and a 10 speed cassette from 34 - 11.  We have a cadence of around 90rpm (we’re ‘spinners’ rather than ‘stompers’ and like close ratio gears).  This gives a speed range of roughly 6 mph to 32 mph @ 90rpm.

My (approximate) calculations for our gearing spread in inches are in the figure below.  We spend the vast majority of our time on the middle ring which will take us from 8 mph to 25 mph (ignoring cross-chaining).

I’m pretty sure the seven speed cassette was the first one to use Shimano’s HG design freehub, so any HG type cassette up to 10 speed will fit.  An 11 speed MTB (not road) cassette should also fit.

My configuration uses a Spa cycles tandem chainset, Tifosi cassette, Shimano RD591 SGS rear derailleur, and Shimano Deore  FD-M591 (66 -69 Degree) front derailleur.  The Spa chainset should have a 116mm axle bottom bracket, but mine works fine with a 122.5mm although it pushes the chainline out a little bit.  The derailleurs are actually 9 speed, but work perfectly well with my wireless shifters set up for 10 speed.

Moving to a double or triple chainset would involve quite a lot of work and you might actually find it more cost effective to look out for a 2nd hand machine closer to your requirements.

My ‘Top of the head’ things to consider for your potential upgrade:

New / 2nd hand tandem chainset
Bottom bracket axle width – new BB’s needed?
Derailleur capacities.  I don’t think you’d be able to find a front derailleur with a total capacity of 22 teeth and a large ring of 52 teeth.  The maximum chainring my (old style) front derailleur supports is 48 teeth.
Cassette compatibility – is your present freehub an HG type?
Front and rear shifters – no shortage of 9 & 10 speed shifters on ebay.
Cabling runs for a double / triple setup.

Would a simple change of cassette, rear derailleur & gear shifter to a 10 speed system give you enough of boost to your gear range?  Much cheaper and simpler to install & lots of 2nd hand stuff on ebay.  

Note: I've assumed you have a freehub not freewheel system, but most comments are still valid

What you are proposing sounds feasible to me.

I have a Specialized hybrid which has a Shimano Tiagra 9 speed triple set up with 11- 32 cassette and 30 / 39 / 50 chainrings.  A Tiagra FD can go to 52 teeth with 22 tooth capacity I believe.

Most new(ish) MTB or Trekking triple FD’s only go up to 42 tooth maximum chainring size.  Older ones like Deore XT accommodate larger chainrings.  Road double FD’s still take large chainrings, but you need a triple FD.

I suspect your rear derailleur will be fine, going from a maximum of 28 to 32 shouldn’t be an issue.  Shimano maximum capacity limits are usually quite conservative and you can normally get away with a 4 tooth increase over the stated maximum if needed.

Front derailleurs are usually tolerant of a bit of mis-matching and can take a bit of ‘tweaking’ if required.  As far as I can recall, the pull ratio of FDs is the same across all Shimano shifters.  I don’t think there is a 7 speed FD which would accept a 52 tooth chainring.  A 2nd hand 9 speed Tiagra FD may let you run a 7 speed chain, though you might need to ‘trim’ between chainrings.  STi shifters allow for this, or old style ‘thumbies’ / SRAM Gripshift / Shimano Revoshift do the same thing.

It’s worth pricing up the cost of three new chainrings versus a whole new chainset.  I have a few bikes with Spa Cycles TD2 triple chainsets (but check the bottom bracket axle length on your present chainset) and it is usually about the same cost to buy a new chainset than 3 x individual chainrings.  Hope this helps.

Thank Lawrence that helps especially to now know how to do calculation. Going to get Stuart to count the teeth so we know exactly what we have at present & if we have a free hub or free wheel. We managed to get up cheddar gorge hills are painful but we manage. We live in Hertfordshire so pretty hilly 

Hi Joanne, it was Edmund who posted a quick method to calculate gear inches rather than myself.

There are lots of calculators / apps available on line to give you quick readings of cassette / chainring combinations.  For example: http://yojimg.net/bike/web_tools/gearcalc.php

I'm inclined to agree with Edmund's comment regarding your proposed low gear.   29 inches is pretty high for a tandem bottom gear - a lot of people happily twiddle away with sub 20 inch low gears.   Someone like me, who is very definitely in the 'over the hill' club, certainly needs the low range of my triple setup.