Talbot Frameworks Tandem - Sik Fadez Family Chariot

If you look at how most are put together it's just the bottom(?) tube that's different from normal bikes.

Depends where you look, but there are tandem tubesets and there is the option to use the beefiest solo tubes for the ones which are the same as solo frames. Also a pretty large range of possibilities in plain gauge 4130. I'd want the pilots downtube to be pretty stiff, as that combined with the drainpipe is the backbone of the chassis.

Definitely worth looking at the Things' blog: http://blog.tandemthings.com/

They used their Tandem for RAAM, which has some big long descents on it (especially in Colorado) and they've done a whole bunch of other rides with big descents.

They've got a Paketa tandem (magnesium) with Di2 plus some other fancy bits (such as an adapted drivetrain so that the timing chain is on the same side of the drive chain, so there's less power put through the frame laterally and so less frame flex).

Don't even want to think about the cost though.

Hello :)
In the limited discussions we've had on tubing, there was talk of Reynolds 853 main tubes, Deddacai chainstays, Columbus Zona seat stays, Paragon Machine Works dropouts, a custom turned T45 headtube and EBB shell.

Awesome, will have a read!

Sounds good! Matt certainly does seem to like a new challenge :-)

*goes back to work on giant cargobike drawings *

Found this in my flickr feed earlier today... Beefy and modern, but with a different approach structurally...

I would consider skipping the stem-to-seatpost solution and going for an extra 'headtube' and use this for both structure/strength and stem holder. Maybe... ;-)

Is that going to have a baby seat between the pilot and stoker?

Could be. I haven't investigated it. https://www.flickr.com/photos/clockworkbikes/18597489284/in/photostream/

All this thread has done is stoked my desire to get back into tandeming. Shame LadyLiz fecking hates the things :(
Want a modernised Herse-style in stainless, curved seat tube with TA/dura-ace and posh cantis...

Was gonna buy a house next year but now not so sure...

I would consider skipping the stem-to-seatpost solution and going for an extra 'headtube'

How come? Wouldn't the alu stem be lighter and give you more options for adjusting length then an extra headtube?

(Although I can't for the life of me work out how you get it on/off)

Edit: its steel and I think it's brazed on so ignore me.

Maybe I was unclear. The above picture just got me thinking if it could be done differently. I don't think the frame above is nearly as clean as 7ven's sketch. (Croft's sketch??)
It is just that the stem height of the stoker is determined by the seat post height of the pilot. It would make the frame more flexible in the future if it could be separated, and if you could use that for actually stiffening the frame it would be a win win..

@7VEN: FSA SLK Light is shit. I have just had the threaded alu insert come loose in the drive side arm. FSA is pushing the responsibility over to danish local dealer who refuses to do anything about it.

It is just that the stem height of the stoker is determined by the seat post height of the pilot
What do you mean by this? It's unusual for a stoker to want a stem higher than the pilot's saddle, and the stoker stem can go up and down on the seatpost.

This came up in my tandem thread a while back as an alternative, but that doesn't mean it's a good alternative...
http://www.bikequarterly.com/images/BilenkyTandemFull.jpg

(urgh shitty Microsoft edge is messing with my formatting, pic supposed to be at end, text supposed to be quote, etc)

You are right. I am not sure what I mean. I will try and sketch it when I am near paper and pen.

Right, I've had a bit more of a look it this and the more I look at it, the more I like the idea of having the transfer belt on the right side inboard of the main drive rings. Good weight savings according to Paketa as you're eliminating one spider-mount arm.

This is what Paketa have to say on the subject:

Custom Yoke to mount timing belt on drive side
The CAD-designed, CNC’ed chain stay yoke is a Paketa exclusive. Who else but the company that's been working with magnesium exclusively for ten years could engineer this subtle work of art? Paketa introduced the worlds first - and still the only - magnesium tandem in 2005, and brings more experience in magnesium bicycle construction than anyone on the planet. The yoke design allows the transfer sprocket to fit in as close as possible to the center line of the frame, yet still provides enough clearance for up to a 28 mm tire—enough for even Clydesdale-class tandem teams to enjoy the benefits of a light weight Paketa tandem.

So I guess you would need a special chain stay yoke to acheive this?

Also, can someone explain what they're doing with the main crank set to be able to get the gates drive inboard of the small chainring? Some sort of fancy adapter?
From these pictures, I see di2 with Sram. I'm not familiar with Sram so assume that it works ok? So you'd just need two standard cranksets?

^ there's a whole load of weird going on there

So I guess you would need a special chain stay yoke to acheive this?

You somehow need to find a lot of space between the rear tyre and stoker's right pedal. Straight-through drive is a good idea for the sake of both the frame and the rear BB spindle and bearings, but something has to give. I managed to squeeze a 10-speed sync chain past a fat track final drive chain on mine with some 2mm thick chainring spacers. Some touring tandems use cranks with much wider Q-factor allowing a straight through drive with the timing rings outside the final drive rings. Paketa have given themselves a tough job trying to squeeze a wide belt and two final drive rings inside a conventional road crank Q-factor, which is why they have had to resort to their special yoke.

@skinny managed to boil his brakes coming down a mountain in the TCR.

He didn't, he overheat his pads that it lost power.

No scobes

Very helpful Tester, thanks.

Currently cycling to Paris with 6 adults and 6 children. My mate owns this sweet Thorn triple tandem and I reckon Thorn have the extra brake problem sorted with this thumb operated cantilever brake. I reckon if we could mount a direct mount caliper somewhere out of the way, then this sort of setup might be the ticket.

Ooooh my god that must be a fantastic trip!

Saw one of those Thorn triples on ebay for £700. If only we had the space! Have a great trip.

Number of teeth on the gates carbon drive sync sprockets. It appears that they come in 66,69 and 74 tooth configurations. Conventional wisdom suggests smaller chainrings (using chains) wear out faster. Anyone know if this holds true for timing belts?

As long as it's not going to foul anything, bigger is better from a stress/wear perspective.

Friends/LBS owners had a 29er Rohloff tanDOOM built... happy to relay any questions about brakes or other such stuff if it might help...