# couplers



## ki5ka (Dec 17, 2006)

Just some idle questions, inspired by the couplers I saw on Okayfine's last pic.

How many have couplers?
How often do you use them?
Any problems, tradeoffs or surprises?
Would you recommend them?

A parallel question bank for those who don't have them.

Have you ever flown with your tandem?
Have you shipped your tandem ahead of you to a foreign destination?
Have you ever rented a tandem at a foreign destination?
Did you wish you had couplers and your own bike, or was it all good?


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## ds2199 (Sep 16, 2008)

No couplers on mtb tandem
Never traveled to foreign destination with mtb tandem
We have thought about a coupled mtb tandem - someday, maybe?

*Road tandem *
Yes couplers
Yes traveled to foreign destination (3x) and other domestic trips
Never considered renting - too particular about my bikes.


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## ki5ka (Dec 17, 2006)

ds2199 said:


> ...
> *Road tandem *
> ...- too particular about my bikes.


Yeah, that's the feeling I have, if I go, I want MY bike!  How did those trips work out? How much extra did it cost and was it worth it? Were there any problems?


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## ki5ka (Dec 17, 2006)

delete


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## Okayfine (Sep 7, 2010)

We've had our S&S bike 3 years and have yet to travel with it by plane. We've had no problems with the couplers and no surprises. There are tradeoffs, namely the weight gain - not only of the couplers but of the steel the frame ends up being made out of for the S&S bikes.

It was a complicated path that led us to our S&S bike. I wouldn't change it, but it would be hard to repeat it. We had a regular ECdM, broke it, sent it to Ventana for repair, then figured that with the repaired bike (as good as new) it was the perfect time to wheel-n-deal. We sold the frame after 1.5 months of use, put that money towards the S&S, additionally traded in a used Ventana frame for 30% off, and picked up the S&S. I don't see us upgrading from here, so there was that "final frame" that helped with the additional cost.

But, compared to coupled road frames, the Ventana S&S is a screaming deal. The coupler option itself is generally cheaper than on road frames, and Ventana throws in two cases on top of that. 

It was just too good to pass up, giving us the option of taking OUR bike wherever we go. My stoker has future plans to take us to Germany to tour around, and the ECdM will go.


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## ki5ka (Dec 17, 2006)

I am very interested in hearing first-hand accounts, I really should wait for more responses before I tip my hand here and deflect the conversation, but I'm impatient so here it is...

I once read a story about a world-traveling kayaker who would cut his kayak in 2, stuff the stern into the bow, then check it as baggage. When he arrived at his destination, would epoxy it together, go paddle, then repeat the routine when it was time to go home. Brilliant! With a reasonable understanding of the manufacturing process, making a structurally sound joint is not difficult and he successfully did this many times over, and he wasn't doing class 3 rapids either  

I keep thinking that would be an interesting approach to our aluminium tandem frame. Fabricate 2 fluted sleeves that would fit inside the frame, cut the frame, epoxy the sleeves in place at the destination, ride, then heat the joints to soften the epoxy to disassemble, VOILA! 

If you haven't worked with epoxy before, you may not realize just how remarkably simply it is to work with. Epoxy joints are routinely used in high-stress, critical applications in aircraft, spaceships, sailboats, racecars, etc... so it seems a reasonable idea. The concern is the epoxy to Aluminum interface. That is more demanding than our kayaker's situation, where he was making the joint with the same material as the original manufacturer. 

Other issues I expect would be critical to success would be accurate alignment, tapered sleeves to reduce the stress risers that would be created... but those don't really seem too complicated. Seems to me that if you can do it with SS couplers, then the stress risers must not be too critical an issue. Alignment could be accomplished by fixing a keyway across the joint before cutting. Cleaning the gluing surface with acid the first time would be simple enough, but subsequent couplings would require some method of reaming out the old epoxy....

like I said, just idle thoughts... that have been fomenting for years.... waiting patiently to be realized... LOL


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## Okayfine (Sep 7, 2010)

Heh, that's quite the plan. I'm not an engineer and I'm not up on the latest epoxy formulations, but I have used various epoxies on various materials and joints over the years. Aside from everything else I see wrong with your plan, with a stoker on the back of the tandem on any sort of terrain, I don't see how you could have 100% confidence in your proposed creation. Without 100% confidence, would you put your stoker on the back?

I've seen a tandem frame crack and fail during use, one that was fully welded with uncut tubes.

Ventana *makes S&S frames*. I don't see any reason at all to contemplate doing this to a frame, much less actually doing this to your frame. It doesn't seem, to me, to be a reasonable idea in the slightest. :nono:


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## ki5ka (Dec 17, 2006)

Yeah, that was the reaction the kayaker got. This is of course, why it has stayed in my mind, and not in public view, for a long time.


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## Okayfine (Sep 7, 2010)

Well, the kayak splits apart, dude goes in the water. Big deal, he's probably already wet. Tandem breaking in half at 20+mph on a rocky descent...much bigger deal. Just sayin'...

Have you looked into the actual S&S coupler? There's a mechanical interface, and the threaded part just keeps that mechanical interface secured. There's also the problem of you heating the tubes to break down the epoxy - depending on the heat necessary, you could take the heat treat out of the aluminum. 6061, welded, has the strength of a not very strong thing. That's why frames get the T6 head treat, bringing strength back into the material.


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## ki5ka (Dec 17, 2006)

I have not seen one in person, but have seen pictures and it appears that these couplers must create stress risers. The tapered point is obviously designed to ameliorate that, and apparently this design adequately spreads the stresses they have dealt with, but with the substantial mass and obviously less flexible structure, they still must be causing stress risers. 

A stress riser is formed when one part of a structure has more strength and less flex than the the surrounding structure. This focuses the stress of the overall structure on a particular point, in this case, the frame immediately adjacent to the couplers. 

Concerning heating the frame to soften the epoxy to disassemble the frame.... As I understand the process of heat treating, it involves heating the frame to a temperature that is in the neighborhood of 900 degrees. Heat deflection temperature for epoxy is under 200 degrees and I imagine doing it with a hair dryer or heat gun. 

Aging the alloy to add strength is done with temperatures between 250 to 350 degrees so, if I'm not mistaken, the process would be unlikely to adversely impact the strength of the frame. Of course I'm hoping Sherwood will chime in here though I really don't expect him to for obvious reasons...

Of course, a failure is not a pretty picture to imagine, but I don't see any reason to think that this would increase the risk of a frame failure more than the S&S couplers would, in fact, it seems likely a 4" (as I imagine it) tapered, adhesive joint would be less likely to fail.

Of course, S&S has some years of proof of concept to support their design... something a new idea will never have


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## swiss_toni (Apr 6, 2013)

Q. How many have couplers?
A. We have couplers on our Ventana ECDM which we have had for a couple of years now. We also have an uncoupled Cannondale road tandem

Q. How often do you use them?
A. We have done three trips so far where I have used the couplers. A 3 week trip cycling in Cuba, one week cycling in Denmark and a three week trip cycling round Cambodia. For these trips the bike was setup with rear panniers and touring tyres. Otherwise we leave the bike built up with MTB tyres and ride in the swiss Alps fairly regularly - single trail, mountain descents etc. We are soon going to do a 5 month trip cycling in South America which will be a good test of everything.

Q. Any problems, tradeoffs or surprises?
A1. We cycle in the rain and water ingress has been a problem (our bike has no drain holes in the frame). I now seal the couplers with electrical tape after assembly and that works well at keeping dust and water out. 
A2. When cycling up mountains we sometimes curse the weight of the bike - but travelling with the bike is worth the trade off for us.
A3. Before one trip I lost the special tool used for tightening/loosening the couplers which was stressful. I now have 3 spare so this doesn't happen again.
A4. Flying with the bike in cases means you are limited to circular trips unless you can forward your cases to a final destination after assembling the bike at your start point. This has worked OK for us so far but does influence route planning.
A5. We have ended up getting a van for transporting the tandem when riding within our own country or surrounding countries (we live in Switzerland) as taking the tandem on public transport was getting very stressful - and for me the time taken to assemble and disassemble the bike means that I only want to do it for trips where we have to get a flight.
A6. So far we have not had to pay any special extra luggage fees when flying - but have had a few close calls - it really seems to depend on the airport staff you are dealing with.
A7. I can manhandle the two cases on my own (not super fun but do-able) and have travelled to the airport on public transport and flown on my own like this - not something that I think I would be able to do with a full size wrapped tandem. Exclaimer - I have never flown with a full size tandem so have no experience of this. My experience of getting trains with a full size tandem was enough to put me off.

Q. Would you recommend them?
A. I am happy that we got a bike with them and so far they have performed well without any problems. When on cycling tours it is re-assuring to know that if I need to break the bike down so that it can fit in a small car/taxi/minibus in an emergency I can. 

It does really depend on what you plan to do with the bike, your budget and storage space. We wanted a bike we could ride in the Mountains and one we could bike tour on (the ECDM was a big purchase and adding the couplers made it more versatile - we couldn't justify having a pure MTB tandem and a separate touring tandem and don't have the storage space for 3 tandems). 

We also do triathlons and having a road tandem without couplers means we cannot travel to far flung races easily - which is shame and something I would like to change in the future.

If I had unlimited funds I would get an uncoupled ECDM to make it easier on the ups (or coupled carbon/aluminium MTB if it existed), a coupled touring bike and a nice coupled carbon calfee. So having re-read my response the short answer is yes


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## Okayfine (Sep 7, 2010)

ki5ka said:


> Fabricate 2 fluted sleeves


Where are you cutting your frame that you only need two sleeves?


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## ki5ka (Dec 17, 2006)

Indeed! You will, I hope, be generous, and note the word "idle" in my original post.  

I didn't even look at my bike, just went off my memory of bikes I'd seen with S&S couplers, apparently not tandems...  Of course you are right; not only would it take three, but two different sizes as well!


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## ki5ka (Dec 17, 2006)

Toni, Thanks for the great reply! Got me thinking about several issues I hadn't considered, which was the point of my post


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## Okayfine (Sep 7, 2010)

ki5ka said:


> Of course you are right; not only would it take three, but two different sizes as well!


More to the point, I don't see how you will be able to fit the two halves of the frame together using protruding fluted sleeves, given the diagonal tube.


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## ki5ka (Dec 17, 2006)

Okayfine said:


> More to the point, I don't see how you will be able to fit the two halves of the frame together using protruding fluted sleeves, given the diagonal tube.


Another very good point ... so if the diagonal tube sleeve was on the outside rather than the inside, the parallel tubes could be fitted first, then the diagonal splice. Think that would work? ...[pause to go look at the frame]... Nope, that won't work either, the top tube and bottom tube aren't parallel! So ALL (or all but one) of the splices would have to be on the outside. Though that would make it more visible, it would better concentrate the heat on the epoxy under the coupling rather than the frame becoming a heat-sink when softening the epoxy. It would also make cleaning the joint very much simpler.


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## Okayfine (Sep 7, 2010)

In looking at the pictures of our old aluminum ECdM, the only tube the sleeve might be able to go on the outside is the boom tube. The stoker's top tube has fittings for rear shifter and brake cables that will make sliding a tube of any length impossible. The diagonal tube has water bottle cage bosses doing the same. 

An exterior sleeve of minimal length isn't going to provide enough surface area, and you'd have issues applying the epoxy completely...and an exterior sleeve would have to be large enough ID to allow for sliding over the tube and for epoxy for the joint, but any slop in the ID is going to create massive flex issues for the epoxy holding it all together, not to mention your stress risers.

I still don't see it, in any way, viable.


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