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Couplers' Location in Frame Design

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Couplers' Location in Frame Design

Old 04-21-19, 08:27 AM
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Paluc52
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Couplers' Location in Frame Design

In the construction of SS-coupled (or Z-coupled) tandems, are there disadvantages to locating all the couplers in the tubes between the captain's and stoker's seat tubes? An advantage, it seems to me, is that it is easier to pack two triangles, plus a couple of straight tubes. Is there a structural (stiffness) or durability price paid in using this design approach?
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Old 04-21-19, 11:09 AM
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As long as you keep the couplers tight they are more structurally sound than the tubes they are connected to. I believe as long as you can put the uncoupled tandem in to 2 airline legal suitcases the location were the couplers are installed on the frame is correct.
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Old 04-21-19, 01:32 PM
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The advantage to having couplers in front of the captain’s seat tube is that it allows removal of the front triangle without having to remove the timing belt (or chain). This allows me to fit our tandem in the back of our small car by simply undoing the couplers and cable splitters.

Of of course if your rear brake is hydraulic, this point is moot.
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Old 04-21-19, 01:54 PM
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fietsbob 
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FWIW Rodriquez 6 pack travel bikes have S&S couplers on both ends of the main triangle tubes.
plus in the wishbone seat and chainstays
[ BTC are stronger than the tubes they go onto..]



looks like they use 14 of them.. (6 in the solo bikes)

Last edited by fietsbob; 04-21-19 at 01:58 PM.
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Old 04-21-19, 09:27 PM
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Originally Posted by Paluc52 View Post
In the construction of SS-coupled (or Z-coupled) tandems, are there disadvantages to locating all the couplers in the tubes between the captain's and stoker's seat tubes? An advantage, it seems to me, is that it is easier to pack two triangles, plus a couple of straight tubes. Is there a structural (stiffness) or durability price paid in using this design approach?
I'm addition to easy partial breakdown to fit in a car you are able to pack the front section in an S&S case without removing the fork.
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Old 04-22-19, 07:43 AM
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If those are 2" couplers, that's a lot of $$$. Certainly will pack well.
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Old 04-30-19, 06:39 AM
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Lolly, our mountain tandem, only has 4 couplers. We're doing our first flight trip with her 8 weeks from today. Since all of our housings are full length, it will present some challenges I am sure.

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Old 04-30-19, 08:26 AM
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I've built and packed up a handful of tandems with both coupler arrangements. In general, I find having couplers in front of the captain seat tube to be the superior approach. However, some tandems can't be made to fit into an S&S hardcase with that arrangement. Here are the pros of of the front-of-seat-tube couplers:
1. Small head tube / front triangle: very easy to fit in case without fork. Sometimes possible to leave fork installed.
2. (as others have noted) Bike can be partially disassembled for cars/trains without adjusting the sync chain/belt. We occasionally put the tandem inside our hatchback by disconnecting the cable splitters and front couplers. Wheels, seats, fenders, etc all remain installed.
3. Reassembly of the frame tends to be easier.
Cons of loose tubes:
1. Loose tubes can be installed at any orientation or flipped front-to-back. Bottle cages or cable guides could be located incorrectly. For those bikes, it's handy to put some match marks on the couplers.
2. Front triangle and rear triangle are both very large chunks. It can be difficult to nest them together.
Pros of loose tubes:
1. Allows tandems with especially long stoker compartments to fit into S&S suitcase.

In both coupler arrangements, a captain crankarm sometimes has to be removed or reversed.
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Old 04-30-19, 09:52 AM
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Originally Posted by scycheng View Post
If those are 2" couplers, that's a lot of $$$. Certainly will pack well.
That's their 2014 model. Both the year & model name on account of the year introduced & it's 14 couplers.

I think it's around $12-$13,000 dollars. I've met the owners of that commissioned the original. Their bike has 50,000 miles currently and has been on 6 continents.

It fits in carry on luggage...in the overhead bin. Which makes sense. Anything at that price isn't worth being "lost" by baggage handlers or sloppy airlines!
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