What is the biggest dia ratio/tooth count which will shift properly between twin chainrings?

What I'd like to hear is, "I made 32-52 and it worked fine", kind of story.

22-36 works fine. 22-38 was a bit hit and miss.

Rule of thumb is 16 usually. Any more, you may have problems. You'd be very lucky to get 20 working.

And if you're fit enough to want a 52, why do you need a 32?

20 tooth gap will give a poor set of ratios with big jumps .You would be better with a triple and putting a 42 in the middle

Hi Realman,

I'm looking hard at a small wheel tandem for the school run and family trips. Circe Helios, but drive is all on one side, so the stoker has just the two chainrings available. I'd like about 17.5..85" gears, and can't see how to approach that range without going silly with the chainring ratios.

Not a tandem expert – does that mean a triple is completely out of the question?

How about a rohloff? They offer a huge range. You could even stick a compact 34-50 on the front, then use a spring loaded chain tensioner, and you'd have yourself a 28 speed with a huge range.

But if its for the school run and family trips, do you really need a huge range?

Triple is out of the question – in this example.

Rohloff is lovely idea (my other bike is a Rohloff – yes it is), but I can't justify that for a runabout.

I don't need huge range, but 85" top end is not unreasonable for a following wind, especially on a tandem, and that would soon get quite spinny down hills. – . 17.5" is pretty much MTB bottom end and we want that (particularly Mrs MC who will be returning home solo up a steep hill)

what about a 3speed SRAM dual drive hub with a 9speed cassette ? – do you really need an 85 for the school run is more my thoughts , just spin faster …

I think you may have to sacrifice some of the top end gears. Have you riden a tandem before? They absolutely rocket down hills, pedalling or not.

And what's the biggest cassette you can get? 11-34? Put that on with a 34-52 (which you may get away with), and it should be alright?

39-53 works perfectly well on my road bike, with unramped / pinned rings.

I'd go for a sane front split with a really wide range rear cassette.

I have been looking at the Dual Drive, it actually gives then more than I need, but could be good.

If 39-53 can shift OK, I may be able to keep that tooth count and look for 30..44. That would give 17.6..80. Only a little shy at the top, but maybe a go-er.

Thanks

Most Duos for MTB are 29/44 and that works fine.

No they're not, most are smaller, although there are some with that big a gap.

Shimano are doing a 30/44 XTR, that'll be absolutely fine.

how small are the wheels?

shimano do a special group set for small wheels – it has a 9t bottom spocket on the cassette, though not sure the matching hub is up to tandem duty..