Tandem Crankset Advice
 

My wife and I decided to build a tandem for our three year wedding anniversary.

Neither of us are expert bike mechanics and we know a decent amount about bikes, but we aren't super geniuses when it comes to this sort of thing. We've been researching components over the last few months and the pinnacle of our setup will be a Rohloff Speedhub, no derailers will be on this bike.

The last group of things we need to decide on is a crankset and everything that goes with it (pedals, cranks, bottom brackets, chainrings, chain, etc.).

I'm having a somewhat difficult time figuring out what our options are. Seems like you can buy a complete 24/27 speed setup for a pretty penny, or you can buy individual components, but I'm not familiar enough with the unique nature of tandem cranks to be completely comfortable with that.*

Considering the derailerlessness, what should I be looking for?

The tandem will be used for 30-70 mile day rides on paved paths initially, and eventually for touring.

Tandem Crankset Advice
 

Can you give more details on the bicycle and components? You mention "derailerlessness", so are you planning an IGH build?

Yeah, the Rohloff Speedhub is the IGH.

BB7 brakes, Velocity Aeroheat rims, Schwalbe Marathon Racer tires, SON dynamo hub in front, Rohloff in the back, Rohloff twist shifter.

You can use any pair of double chainring (standard) cranksets you like with the Rohloff, as it doesn't require a tandem crossover crankset.

You install them with just one chain ring up front and two rings in back with the sync chain on the same side as the drive chain.

It's the easiest set-up you'll find on a tandem.

Bottom brackets will be dependent on the type of chainrings you select and the chains don't need to be anything special; what ever is compatible with the Rohloff will do for both the drive & sync chain that connects your front crank to the rear crank.

Well, now that you mention it, it seems kinda obvious. :D

Are there any considerations for the sizes (or ratios) of the chainrings that I need to be aware of?

The gear inch calculation is still going to be calculated from the captain's chainring in relation to the sprocket on the Rohloff, right?

Thanks!

From Rohloff, here are the recommended chainring / rear sprocket combinations: "If mounted on a tandem or if the rider weighs over 100kg, the following sprocket ratios must not be undercut: 34/13, 38/15, 40/16, 42/17."

For your timing rings, anything between 34t and 42t will work. If you're building a custom tandem you could even build it to be chainless using the Gates Carbon Drive - drive belt and tandem sync belt, although using the Gates timing belt requires that you use either a 28.5" or 27.75" stoker compartment based on the available timing sprocket/pulley sizes.

No, the gear-inch calculation is done from the drive ring, which is the stoker's chainring. The captain's chainring is a sync ring.

You say that you are going to "build a tandem"; does this mean that you are going to find a tandem frame and build it up yourself, or do you plan to have it custom-built for you?

Some things to consider:

1) Rohloff spacing is 135mm, not 145mm like most modern tandems.
2) You will need to account for adjusting the tension on BOTH chains, not just the sync chain (ours has two eccentrics.)
3) I have heard that Rohloff now has 36-hole hubs available; I would make sure I got one of these.
4) Two standard double cranksets with same-side drive works great. In the captain's position, use the inside ring as the drive (sync) ring. Mount on the outside another ring that, with the teeth ground off, is the same size as the drive ring. This will make the crankset look more finished and serve as a bash ring.

We're actually on the fence about this right now. I have a frame builder friend who has expressed interest, but hasn't ever built a tandem before. If we go this route we will definitely do a Gates Carbon Drive.

Here's my understanding of what we're looking at, please correct me if this is wrong:

There are four toothed things that are necessary: captain chainring (sync/timing), stoker chainring (sync/timing), stoker chainring (drive), and Rohloff sprocket.

The captain chainring (sync/timing) and the stoker chainring (sync/timing) are connected by a chain.
The stoker chainring (sync/timing) and stoker chainring (drive) are connected physically.
The stoker chainring (drive) and the Rohloff sprocket are connected by a chain.

The stoker chainring (drive) will be 44T and the Rohloff sprocket is 16T. (nominal numbers)

Do we want to match the size of the stoker chainring (sync/timing) and stoker chainring (drive)?
Is this even possible if we are using a double chainring?
Is this something we would want to do if we were using a tandem crank that has a chainring on either side of the frame?
Does a tandem crank that has a chainring on either side of the frame require special parts or can we assemble this from normal parts?

Do we want to match the size of the captain chainring (sync/timing) and the stoker chainring (sync/timing)?
If not, what are the potential benefits/downfalls of this?
If we are using a standard tandem crank for the stoker, do we need a special setup for the captain, since the chainring is on the left?

I really like this idea.

Thank you so much for your time... it's much appreciated.

I was in the same situation and was told by many people you should go with someone who has built tandems before, but of course this was when I was also gonna pay for it.

Correct, it should look like the right example on this diagram(except your rear won't be a triple)

http://i248.photobucket.com/albums/g.../TA_tandem.jpg

As long as both sync chainrings match, you will be fine.

You can assemble a tandem crankset from normal part, but you will need to do something to correct the backwards pedal threads. You would need three driveside cranks and one non-driveside arm. Two of the ds arms would need the pedal threads helicoiled since they will be on the opposite side and the one nds arm will also need it. It will look like the left on the above diagram and I'm sure you could figure out what goes where. I am actually thinking about doing this with some Campagnolo cranks I have, Just need to find a triple driveside arm.


No need to.

Either a captain's set or a standard crankset flipped and the pedal threads heicoiled.

Now to add a bit more to the discussion:
What length crankarms do you want for stoker and captain?
Put your thinkling cap back on !
Planning out a new tandem is always a bit of a challenge, but fun!
Pedal on!
Rudy and Kay/zonatandem

Ahh... and here is where everything get's terribly complicated! We are currently using 155mm cranks on our respective bikes and I'd like to experiment with something a little smaller.

It seems like the short crank movement (or trend, if you prefer) hasn't yet hit tandems.

Three things initially prompted my post: inability to find simple cranksets for the Rohloff, inability to find a crankset that didn't seem oddly expensive, inability to find a crankset that came standard with cranks shorter than 160mm.

I think I'm getting there. :P

The trend toward shorter cranks is only with tri/TT bikes as far as I know. They are doing it so they can get their torso lower and still maintain suitable torso/thigh angles at the top of the pedal stroke. This would not be applicable to hardly any tandems.

Paper asked:
Do we want to match the size of the captain chainring (sync/timing) and the stoker chainring (sync/timing)?

Veggie, unless I misunderstand Paper's question, the captain and stoker chainring (sync/timing) must match, or else they will be WAY out of sync most of the time. This will lead to having difficulty with some turns, as the Captain has no way of knowing or changing the position of the stokers pedals when encountering a corner. Even having the Captain and Stoker OOP (out of phase) is okay as long as the Captain knows where the stoker's pedals are, but with differing size chainrings, he will always be guessing - or have to communicate this with the stoker while trying to negotiate turns.
Leave the sync/timing chains the same size whether staying In Phase or Out Of Phase.