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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 06-29-11, 03:16 AM   #1
ftwelder
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Tandem from the ground up.

Hi, My wife and I enjoy riding together and after riding an old Schwinn around a bit we have decided to build up a tandem for road riding.

I make bicycle frames for a living and have some of what I need to make build a tandem frame from 7005 aluminum. I don't care for the EBB solution for chain tension so I will make some type of tension or guide system. Mostly because of the time it takes me to position my saddle.

The strongest/largest head tube platform I have available in 7005 is a large 2" diameter tube to fit the 44mm cups (1-1/8 flush). I have cutters for onepointfive but no tube is available to accommodate those cups. A very large 65mm tube will be used for the down and boom tubes. I am not sure how much shaping I want to do on the boom tube (perhaps just shape the ends rectangular to fit BB shells) but the down tube will be bi-round and 75X50.
I am going to use paul brakes at the rims and a BB7 mounted to a triangulated seat stay (actually an MTB chainstay used as seat stays).

I have the front drawn to match my current road bike and stoker Lanie is short and likes an upright position so the back is 28"

The parts
Middleburn cranks
Paul brakes
29'r wheels (135)
BB7 dragger
Thomson stem/custom
3T bars
9 speed 105/XT
(proposed gears) 53/38/28
11/26 rear

proposed frame


tandem by frankthewelder, on Flickr


More pics as some progress is made. Thanks for lookin'
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Old 06-29-11, 06:34 AM   #2
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I would reconsider the way your are planning to adjust the front chain, I have the Bushnell ECC on our new Calfee and it works great. I have had Santana's in the past and their system works fine also. Years ago I built some homemade tandems and tried a guide on the first one but on the second one I set it up so that the front BB slid back and forth for adjustment, it worked much better than the guide. Just my thoughts.

Wayne
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Old 06-29-11, 02:05 PM   #3
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Hi Frank;

A couple of suggestions:
* go 145mm at the rear - the hub is more expensive, but will last a lot longer.
* I think that you'll find that you want something lower than 28/26 if you do any major hills; make sure that you have the ability to do 28/34.
* which Paul brakes? http://www.paulcomp.com/brakes.html
* with respect to the boob/boom/bottom tube - make it as wide as you can; it is subject to lots of side to side bending loads, while the up-down loads are shared with other tubes in the frame. This should be the focus of your structure.
* the down tube does not need to be as stiff or as strong as the boob tube.
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Old 06-29-11, 02:19 PM   #4
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By saying "BB7 dragger" it sounds like you're planning to use it as a drag brake. That brake is not designed for that kind of use - you can use it in a normal way as a third brake, or otherwise get a proper drag brake.
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Old 06-29-11, 02:37 PM   #5
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Originally Posted by DubT View Post
I would reconsider the way your are planning to adjust the front chain, I have the Bushnell ECC on our new Calfee and it works great. I have had Santana's in the past and their system works fine also. Years ago I built some homemade tandems and tried a guide on the first one but on the second one I set it up so that the front BB slid back and forth for adjustment, it worked much better than the guide. Just my thoughts.

Wayne
Well... he has his reason, as it seems he is concerned about any alteration of the seat/BB distance once it has been optimally set. I have two tandems, one with and eccentric and the other with an idler. With the eccentric the movement of the BB is really slight and I for one don't notice the difference. Idler systems are strongly associated with low end department store tandems. I think that is mostly because they are made badly and cheap. A homebuilder can probably make an idler system to a higher level of quality than is usually the case. There is, however, plenty of space along that boom tube for a different system. A third timing chainring for instance.

H
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Old 06-29-11, 02:46 PM   #6
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* I think that you'll find that you want something lower than 28/26 if you do any major hills; make sure that you have the ability to do 28/34.
I agree, but I think it is asking a lot of a cassette, even a 9sp, to cover 11 - 34. We left the 11 - 28 alone on our rig and dropped the 28 up front to a 24! It really is a better way of getting a nice low granny when you need it, but preserving those 11% shifts on the rear that keep your cadence in the zone. FWIW.

H
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Old 06-29-11, 04:03 PM   #7
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That sounds like a cool project. I wish I could weld.

Most tandem bikes look relatively similar. But they're always conversation pieces and fun to talk about in group event rides, etc. Since it doesn't sound like you and your wife plan to race it or anything, I think you should make it a little wilder than your drawing. Maybe some curved tubes to make some aesthetic flow or something. Have fun with it and have a conversation piece!
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Old 06-29-11, 05:42 PM   #8
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Make sure the stoker geometry will handle a suspension seat post just in case. Some teams are fine without, others swear by their Thudbuster.
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Old 06-29-11, 06:35 PM   #9
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Looks like a neat project. I would enjoy pictures as the project develops.
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Old 06-29-11, 08:16 PM   #10
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Another possible option . . .
No idler or eccentric is really required.
Chain stretch on crossover chainrings can be manipulated.
When chain loops more than necessary, replace 1/3 section of cross over chain with new chain, thereby eliminating the stretch part. May only need to be done once or less per year depending on annual mileage.
Or . . . when stretch occurs 'float' a chainring slightly larger than the crossover rings . . . makes for a great/interesting conversation piece.

Also concur with the 145mm spacing suggestion.

Suggest an adjustable stoker stem . . . amazingly my stoker after 30,000 miles on our present tandem wanted the bars brought in a tad closer.

Pedal on TWOgether!
Rudy nd Kay/zonatandem
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Old 06-30-11, 05:34 AM   #11
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Wow, tons of good information! I don't disagree with and of the proposed improvements and I appreciate your feedback. I have a lot of bikes and a lot of "some" parts to make frames with. here is sort of a run-down of other things with time and money mixed in. I personally get stoked on something and build it. I don't really have a "theme" or long term plan other than riding a road tandem soon. I have been building custom frames for 30 years, my system is DO IT NOW. Thinking about it is causing a lack of efficiency right now due to daydreaming. If I just do I will be fine and other things can get done.

EBB: 7005 tube is difficult to get and only available is some sizes. I don't really want to do all the tooling/set-up and programming required to make one frame component for a bike I may not even like and need to change.

drop spacing: can't get 7005 bar stock for a decent price and forged 7005 drops have sloppy tolerances and rounded corners that won't support high torque for a really long time. I also can't really budget a dedicated set of awesome tandem wheels to be able to ride this summer.

I love smooshing tubes so there will be a bit of that going on. I don't want to risk wasting tubes so courage may be a bit weak.. This had small diameter tubes so I could get very radical on this. This was all straight tubes to start. a 16" for a baby girl.


27 082 by frankthewelder, on Flickr

Last edited by ftwelder; 06-30-11 at 05:38 AM.
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Old 08-12-11, 04:12 PM   #12
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Hi, I made some progress and completed the frame today (unless I forgot something) I ended up sourcing a piece of extrusion that was perfect for the eccentric BB device so that was a plus. The first couple of pics are during the build process and then a couple with it "posing" across the street from my shop.

The down tube and boom tube are both 2-1/2" diameter. I flattened the boom tube to 2X3 and squared the ends to fit the BB shells. The down tube is bi-axial flattened with the ends squished to match the head tube and BB shell. The chainstays were made for tandem use but the sea stays are very thin butted chainstays.

Since the front seat tube has nothing bolted to it, I made it 1-1/2" in diameter (very oversized) with a 30.9 or 31.6 post (depending on what I ream it too) The headtube is 44mm. I think I kept the angles the same as the pic above but I made the head tube longer and the stoker seat tube shorter.

Enjoy the pics


28 002 by frankthewelder, on Flickr


28 004 by frankthewelder, on Flickr


28 003 by frankthewelder, on Flickr


28 001 by frankthewelder, on Flickr


28 014 by frankthewelder, on Flickr


28 011 by frankthewelder, on Flickr
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Old 08-12-11, 09:05 PM   #13
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Lookin' good!
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Old 08-13-11, 01:53 AM   #14
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Quote:
Originally Posted by rdtompki View Post
Make sure the stoker geometry will handle a suspension seat post just in case. Some teams are fine without, others swear by their Thudbuster.
I'll second that - my stoker would never go back now she has a thudbuster - and the long travel one needs some serious space back there! Also I take it that 28" measure is the seat post to seat post along top tube - I just measured our 'dale, which is quite an old one and I believe reviewed as having a "cramped" stoker compartment maybe - and it is 28"... just thought I should mention that, but it all depends on stoker physique and preference I guess and I suspect you guys have trialed a few tandems so have a feel for that....

My main feeling here echoes a little the poster who mentioned curves and suchlike - but have a blast - this will be one tandem that will be seriously unique (they all are, but this is super special!).

Last edited by Mainframeguy; 08-13-11 at 08:36 PM.
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Old 08-13-11, 05:50 AM   #15
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I'll second that - my stoker would never go back now she has a thudbuster - and the long travel one needs some serious space back there! Also I take it that 28" measure is the seat post to seat post along top tube - I just measured our 'dake, which is quite an old one and I believ reviewed as having a "cramped" stoker compartment maybe - and it is 28"... just thought I should mention that, but it all depends on stoker physique and preference I guess and I suspect you guys have trialed a few tandems so have a feel for that....

My main feeling here echoes a little the poster who mentioned curves and suchlike - but have a blast - this will be one tandem that will be seriously unique (they all are, but this is super special!).
I just slapped myself in the head when I remembered seeing mention of the suspension seat post. The diameter is only 27.2. I can build a small linkage suspension under the saddle if the post size I selected is too small.

We didn't sample any tandems before building this one but I can tell you she wanted the bike to be small enough so she could "ring my neck" without getting off the bike (J/K) . Lanie is 5'3" tall. She also likes an upright riding position and prefers Northroad style handlebars on her bike. I am sure if this one is fun we will build a more serious machine in the future with several refinements. I purchased enough material for two frames. is 10.5 lbs in the ball park?

Thanks for the kind words!
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Old 08-13-11, 06:39 AM   #16
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Would be willing to make a frame for others? I am very impressed with your work!!
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Old 08-13-11, 07:27 PM   #17
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Would be willing to make a frame for others? I am very impressed with your work!!
Let me see how this one works, I am not as easily impressed as I am flattered, thank you.
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Old 08-13-11, 08:57 PM   #18
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It looks like you have good clearance for fairly wide tires in back. With wide tires at lower pressures you can most likely use a regular seatpost rather than a thudbuster. Many hear run 25mm tires at 120+ psi and then require a seatpost.

Also consider a sprung Brooks saddle. It is a great option rather than a thudbuster seatpost. A Finesse womens single rail leather saddle with springs will save money and weight over a plastic saddle and thudbuster seatpost.

What are you using for a fork?

Wayne
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Old 08-14-11, 06:24 AM   #19
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I purchased enough material for two frames. is 10.5 lbs in the ball park?
Our Calfee Tetra with headset, bottom bracket eccentric and seat bolt clamps weighs 7 pounds. Their Dragonfly model is a pound lighter. What is your target weight for the completed bike?

Wayne
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Old 08-14-11, 06:36 AM   #20
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Let me see how this one works, I am not as easily impressed as I am flattered, thank you.
thanks I am watching this thread with interest, can't wait to see the complete bike.
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Old 08-14-11, 07:32 PM   #21
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2000 Santana Arriva steel frame 8/5/8 tubing no headset or bottom brackets weighed 11 pounds. Lateral tube weighed 2 of that 11.

Wayne
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Old 08-15-11, 04:35 AM   #22
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Our Calfee Tetra with headset, bottom bracket eccentric and seat bolt clamps weighs 7 pounds. Their Dragonfly model is a pound lighter. What is your target weight for the completed bike?

Wayne
That is a pretty impressive weight. There aren't many choices for aluminum materials these days but I am sure I could drop 500 grams or so with little effort.

I didn't have a target weight or any pre-conceptions at all except to build a fun bike! My best method is to do a minimum amount of research and discard or recycle the first few examples after I learn what could be made better. I made many assumptions regarding the amount of flexing that will take place and I am sure it would be very challenging to make a bike any stiffer than this one. Too stiff may be good while we struggle to learn to ride tandem.

I ended up with a lot of tire room for sure. The roads around here are in really bad shape and I am sure much of our time will be on the amazing remote dirt roads we have in the area.

I am leaning toward John Deere colors, green with yellow stickers.

I was thinking about just banging out a steel fork but someone in "framebuilders" suggested dual crown aluminum which would be really fun to make! (though it would take a long time)

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Old 08-15-11, 10:42 AM   #23
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That is a pretty impressive weight. There aren't many choices for aluminum materials these days but I am sure I could drop 500 grams or so with little effort.

I didn't have a target weight or any pre-conceptions at all except to build a fun bike! My best method is to do a minimum amount of research and discard or recycle the first few examples after I learn what could be made better. I made many assumptions regarding the amount of flexing that will take place and I am sure it would be very challenging to make a bike any stiffer than this one. Too stiff may be good while we struggle to learn to ride tandem.

I ended up with a lot of tire room for sure. The roads around here are in really bad shape and I am sure much of our time will be on the amazing remote dirt roads we have in the area.
Wow, this is sounding like a cool tandem. I didn't notice before that you're building it for a 29'er wheelset. With disc brakes, you'll easily go from a cool fire-roads bike with 29'er wheels and knobbys, to a road-touring bike with 700c disc wheels if desired. Wish I could do that! (And if the frame is a little over-built for road riding, it'll still be useful for loaded touring if you ever decide to try that later.)
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Old 08-15-11, 10:06 PM   #24
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Looks great. 28" is plenty of length for the back.
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Old 08-17-11, 12:51 PM   #25
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Thusbuster can be purchased with shims to make it fit almost any size seatpost.
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