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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 03-11-12, 06:45 PM   #51
rhino919
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I wanted to apologize if that came off as sharp / snippy, I was trying to go for clarification per-se.
No offense was taken (at least by me). I often find it difficult to effectively communicate everything I want to with written communication, and it is easy to have someone misinterperet what has been written. So, I try to give people the benefit of the doubt as to their intentions, and hope that people will do the same for me. Plus, it's not like we are discussing a life or death issue here (it's just a bicycle for Pete's sake). No point in getting all worked up about it.
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Old 03-12-12, 08:08 AM   #52
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At $1,300 to $2,500 to add them, S&S couplers wouldn't have fit in the budget. However, if there was no additional cost for the S&S, I would still choose the English method, as I think it is a more elegant solution.
1) It allows for easily changing to different tube materials or thicknesses, although you could argue that a correctly designed frame shouldn't need this option.
2) It eliminates the eccentric BB. To tension the timing chain you clamp the top tube and one end of the boom tube in place, push down on the seat to tension the chain, and clamp the other end of the boom tube.

I do see some potential issues that may not make it suitable for everybody.
1) The clamp bolts must be torqued correctly to make sure the tubes don't slide while riding.
2) The tension of the chain will vary depending on how hard you push down on the seat.
3) The length of the bike could vary a little (+/- 1mm?) from assembly to assembly which would require adjustments to the derailleurs.

At this point, I'm perfectly happy to deal with these issues. Once I actually get the bike, my opinion may change.
Having owned a Bike Friday tandem, and a bike with S&S couplers, IMHO it's a less elegant solution.

You have to fuss with it every time you reassemble the bike to get the tension right on the timing chain.

And as you noted, you have to adjust the deraileurs each time you reassemble, which in my experience could take a bit of effort to get dialed in precisely.

To me, it's a lower cost option with some tradeoffs.
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Old 03-12-12, 08:47 PM   #53
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Having owned a Bike Friday tandem, and a bike with S&S couplers, IMHO it's a less elegant solution.

You have to fuss with it every time you reassemble the bike to get the tension right on the timing chain.

And as you noted, you have to adjust the deraileurs each time you reassemble, which in my experience could take a bit of effort to get dialed in precisely.

To me, it's a lower cost option with some tradeoffs.

Thanks for sharing your experience. It is quite thought provoking. I agree that in area of derailleur adjustment, S&S couplers are most definitely superior.

So, I've been thinking a bit about the assembly process and how to eliminate, or at least minimize, the need to adjust the derailleurs. I can think of three variables that will cause the boom tube length to change:

1) Pressure on the seat prior to tightening the last clamp - It seems to me that with a little practice this could be consistent enough that it won't be an issue.

2) Non-concentric chainrings changing the length depending on orientation - Supposedly Davinci timing rings are perfectly concentric, so this shouldn't be an issue. However, to eliminate any variation, the cranks could be turned to the same orientation at each assembly.

3) Chain wear - This probably won't be an issue from assembly to assembly, but over the long term this is a big issue. My understanding is that you should replace the chain when it reaches 0.5% elongation. For a 31 inch stoker compartment, that equates to almost 4 mm. So over the life of the chain, the derailleur cables will need to get 4 mm longer. That's a lot!! I will probably end up changing out the timing chain much earlier in than I would with an eccentric BB.

What other variables am I missing?

All of these variables could be eliminated by adding an eccentric BB. I'm going to have to think some more about that.
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Old 03-13-12, 08:49 AM   #54
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Let me think about this for a second: add an eccentric or go through the process you just described. In my opinion it is a no brainier, add the eccentric! Why not? You have so much to gain and so little to loose.

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Old 03-13-12, 09:33 AM   #55
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Having owned a Tandem Two'sday in a previous life, I can attest the assembly process wasn't that big a deal and likely no slower than putting an S&S bike together.

There were aspects of the TT we didn't like, but shift quality and ability to assembly weren't among them.
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Old 03-13-12, 10:27 AM   #56
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Agreed! Approx. 3 min. to unscrew, turn, adjust & and tighten an eccentric vs. going through that extensive thought process? No brainer with that one...

I'm new enough to this stuff as it is. Keeping it simple is priority #1.

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Let me think about this for a second: add an eccentric or go through the process you just described. In my opinion it is a no brainier, add the eccentric! Why not? You have so much to gain and so little to loose.

Wayne
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Old 03-13-12, 04:52 PM   #57
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Thinking, Thinking, Thinking
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Old 03-13-12, 04:55 PM   #58
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Thread title changed to differentiate from JSNYC's "New tandem build". Thanks to AllenG!
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Old 03-15-12, 12:06 AM   #59
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I have decided to stay with the current design (no EBB). Once I get the tandem and have assembled it several times, I will provide a detailed report on what is required to get the timing chain tension right and keep the derailleurs in tune. My expectation is that a turn to the barrel adjusters will be all that is required for the derailleurs, but time will tell.

On another note, I'm glad I ordered my tandem when I did. Rob has orders for 5 more bikes in the week and a half since NAHBS and still has more enquiries.

Rob is planning to start ordering parts for the tandem in April and begin construction in May. He said he will be happy to provide pictures of the build process for me to share. What would people recommend as the best way to share the pictures? Just attach them here? Set up a Flickr page? Something else?

I found these videos of Rob being interviewed at NAHBS interesting: Project Right 1, Project Right 2 and SS MTB.
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Old 03-15-12, 06:08 AM   #60
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I think avoiding an eccentric is a great idea. Contrary to other posters I don't see changes in the bike length as a big issue at all. In my experience the eccentric doesn't need frequent adjustment and is a heavy, expensive and sometimes unreliable solution. It's no more effort to do up some frame tube pinch bolts than mess with an eccentric.

Then regarding derailleur cables, once the derailleur end points are set, all you need to do is ride along and play with the inline cable tension adjuster. No big deal at all and can be done in the first 5 minutes of any ride. Or go for Di2 if you must.
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Old 03-15-12, 07:13 AM   #61
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I am not sure this would work but I suggest exploring the option of using cable housing under the boom tube with some slack across the gaps rather than bare cable.

Downside would be some additional friction but with modern cables this might not be a big problem. Upside would be that having slit cable stops on each side of the gap would result in a fixed cable length, the length of the housing. The cable splitter could be placed on the outside of one of the cable stops.

Custom builds are great for using off the wall ideas.
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Old 03-15-12, 08:19 AM   #62
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Originally Posted by rhino919 View Post
I have decided to stay with the current design (no EBB). Once I get the tandem and have assembled it several times, I will provide a detailed report on what is required to get the timing chain tension right and keep the derailleurs in tune. My expectation is that a turn to the barrel adjusters will be all that is required for the derailleurs, but time will tell.
Just to be clear, neither of these things are "big deals". They're just considerations associated with the design, which is what I believe was requested at the outset of the thread.

A tandem with an eccentric will create rider position issues for the captain which the English design eliminates, as does the low-tech idler pulley.

Sync chain wear is another one of those things where new tandem owners just need to wrap their heads around just how long their sync chain is (e.g., the one for the English will likely be somewhere around 84" / 168 links assuming 42t chain rings) with regard to how much a sync chain will elongate as it wears, and how much of an impact the tension adjustment method will have on riding position as the sync chain wears.

Tandem owners with sync chain-equipped bikes (vs. belts and thank goodness the pricing came down on those) exacerbate the sync chain wear / adjustment cycles when they opt to use lightweight chains that typically wear faster vs. say an 8 speed or even a single speed chain. Using smaller timing rings also increases the rate at which a sync chain will elongate.

However, at the end of the day and after riding tandems long enough a couple things become apparent:
1. We learn to live with slight changes in riding positions on our tandems vs. single bikes, including those gradual changes that over time eventually require a re-calibration / reset to correct when they get way too out of whack.
2. We learn that sync chain tension does not typically require precise attention to a certain specification, i.e., it's hard to get one too tight using a simple pin-spanner and they can be pretty loose and still not create a problem except under out of saddle springs or other riding situations where the tandem is moved from side to side that can invite a chain derail at the rear sprocket or cause the chain to get caught by the stoker's crank arm.
The English design is somewhat unique to most conventional tandems in that it will require a derailleur adjustment whenever the bike is re-assembled or when the sync chain needs to have its tension adjusted unless some indexing marks are added along the top of the boom tube near the sleeve that can be used as a guide during re-assembly. Again, even without index marks, it's just an extra step that tandems with eccentrics don't typically have to deal with when quality cable splitters are used and the person doing the re-assembly ensures all of the cable housings are properly seated, etc.

Tandems with 10 (and I suspect 11) speed gearing are a bit more sensitive to even minor adjustments in derailleur cable pull which simply means a little more finese is needed and an easy-to-reach while riding, in-line barrel adjuster is a must for dialing-in the shifting once both the captain and stoker are on the bike.

Again, this a nuance that is somewhat unique to tandems in that you can't induce the frame deflection on a workstand or doing a solo road test that occurs when both riders are actually riding a tandem, and some tandems will have enough deflection under load to require a minor derailleur adjustment while on the fly to get everything dialed-in. The English design does not appear as though it will be immune to this little nuance of certain tandems. But, it's also something that's easy to address.

Last edited by TandemGeek; 03-15-12 at 08:29 AM.
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Old 03-15-12, 10:35 AM   #63
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The continuing discussion on this thread of "eccentric vs. tube length" adjustment has forced me to try and dredge up more memories of living with the Tandem Twos'day. My vague recollections:

1) All cables on the TT ran along the top tube, which did *not* vary in length (assembly required full insertion into it's socket). So shift quality was not an issue.

2) Our timing chain had easily seen removable links which matched up to punch marks on the chainrings, making installation of the timing chain foolproof. Once installed, the cranks were turned to the point where the chain was tightest, then at midpoint between the sprockets I would push the two sections of chain towards each other until there was sufficient force to pull the bottom tube *slightly* further into it's socket. A quick revolution of the cranks to verify appropriate tightness was then performed, followed by tightening the screws which clamped the bottom tube into it's socket.

3) Done.

No idea how applicable this would be to the English tandem.
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Old 03-15-12, 10:11 PM   #64
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Thanks to all for the asking questions and sharing your insights and experiences. It has really helped me to think through this design and build spec more thoroughly. Now I just have to wait until August to see how it all works out.
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Old 04-18-12, 11:16 PM   #65
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It Has Begun!

A pic of a bit of excess material being removed from the headtube:



Any suggestions for a photo sharing site to put all of the pics on?
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Old 04-19-12, 03:47 PM   #66
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Old 04-19-12, 05:39 PM   #67
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Idler pulley for the sync chain?
DI-2 for derailleurs? Bit pricey, but price has come down with the Ultergra version.
Round stoker handrests? Got a custom pair (carbon fiber) for stoker Kay back inb '03. Also had some yellow plastic ones from Italy in '77 and then the DiaCompe version in the 1980s.
Always fun to lay out the needs/wants on a custom tandem . . . have done so 4 times for ourselves.
On our custom tandems we included braze-ons/glue-ons for 2 spare spokes under the boobtube, for our mini garage door opener on stoker's adjustable stem, as well as a custom mount on stoker's stem for her water bottle cage + mount for our Topeak pump on boobtube.

Enjoy the ride TWOgether!
Rudy and Kay/zonatandem
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Old 05-25-12, 04:33 PM   #68
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A bit more progress on the tandem. Since we won't be picking it up until August, Rob has been fitting it in between other projects. (one of which was a full suspension 29er recumbent)


From the left Bottom Brackets, Head Tube, Mid-tube Sockets & Clamp, Seat Tubes, Chainstays, Mainframe Tubes and Titanium Mid-tubes. The BB's, Headtube and Seattubes are all custom relieved/butted.


Main frame loaded in the jig.

The photos are all being stored on photobucket here
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File Type: jpg frame1.jpg (90.7 KB, 30 views)
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Old 06-05-12, 11:48 PM   #69
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It is starting to look like a tandem!





You can see all photos here

Pick-up date is set at August 6. Yay!
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Old 06-10-12, 12:05 PM   #70
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Rob posted a short update and some more photos on his website here.
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Old 06-10-12, 10:01 PM   #71
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Newbie here - without the EBB, don't you have to use a chain tensioner on the timing chain?
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Old 06-11-12, 07:16 PM   #72
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Newbie here - without the EBB, don't you have to use a chain tensioner on the timing chain?
Hi Willhs - that question has already been answered earlier in the thread. Happy reading.
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Old 06-13-12, 06:09 AM   #73
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Thanks, I did read the thread, and that's why I was confused and asked the question. I can see how the wording of my question could lead you to think that I didn't read anything. So, if you don't have an EBB, you can just tighten the chain (or perhaps use a half link?) to get it so you don't need the tensioner? That's actually big news for me, and I would appreciate confirmation of this. I don't mean to derail the thread.
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Old 06-13-12, 06:34 AM   #74
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So, if you don't have an EBB, you can just tighten the chain (or perhaps use a half link?) to get it so you don't need the tensioner? .
I'd pursued the same question early on and missed the subtle nuance of how the actual boom tube length / sync chain tension was achieved. To spare the OP a rehash, here's what he wrote in reply to my question:

Quote:
The tension in the timing chain is set by clamping the top tube in place, clamping one end of the boom tube, pressing down on the seat to tension the chain, and clamping the other end of the timing chain.
In other words, the telescoping ends of the top and bottom tube provide +/- fore/aft adjustment of the boom tube length to accommodate setting the final tension setting of the sync chain.
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Old 06-13-12, 02:42 PM   #75
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Ah, I see. Interesting feature.
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