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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 08-08-09, 01:32 PM   #1
storunner13
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Build tandem frame from two Schwinn bikes?

I'm planning on brazing 2 older road frames together to make a tandem bike. I'm not worried about the wheels, I'm planning on having very strong wheels for the load, as well as installing a new fork and brazing on some cantilever bosses on the seat stays.

The question I have is in regard to the strength of the 4130 tubing used on the Taiwan made Schwinns I'm thinking of using. The smaller stoker size will be a Traveller ('85?) the other will probably be a larger, similar Schwinn. Sheldon Brown recommends mountain bikes with 4130 tubing, but this is a road tandem. What do you think?
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Old 08-08-09, 03:03 PM   #2
zjrog
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I picked up two old Trek 950 MTB bikes, both sort of smaller frames. Both are lugged 4130 frames. I'm planning to order some new tube to stretch the rear bike out a bit at the top tube, for the bottom tube between bottom brackets, and one tube from the rear bottom bracket to the front headtube. Source for the tube is http://www.aircraftspruce.com/catalo...tubing_un1.php, I just need to decide what tube diameter wall thickness to get. When we are two-up, we'll be almost 500 pounds (I'm 300 myself). Hoping to get all this TIG wleded instead of brazed.
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Old 08-08-09, 03:39 PM   #3
zonatandem
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No boob tube???
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Old 08-08-09, 05:25 PM   #4
PMK
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Quote:
Originally Posted by zonatandem View Post
No boob tube???
I agree, if it were me attempting this, and I may for Chopper Nights, I would retain the front frame headtube, downtube, seattube and BB shell. From the rear frame, keep the rear triangle, seattube, and BB shell. New tube wise, fabricate a diagonal, toptube and bottom tube.

Done with some care, the Diagonal can be slid onto the fwd seattube then mitered. After that the bottom and top tubes can be mitered then weld slowly and constantly check alignment.

Getting real creative, lager thin wall tubes can be purchased and have the end reworked / reshaped with heat and some coaxing. Even the bottom tube could be modified from round to oval with some careful press work.

PK
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Old 08-10-09, 04:57 PM   #5
dsmyers
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I did this with two 80s mountain bikes. I cut the seat- and chain-stays off the front frame and the top and down tubes off the rear frame, leaving me with a front and a rear triangle. I used 1.25 inch, 0.9mm wall-thickness 4130 from Dillsburg Aero Works to create a boom tube and marathon lateral tube. The boom tube is actually two parallel tubes, for added rigidity.

It's worked out very well -- I've done a couple hundred miles of road riding on it, including ~200 of loaded touring.

FYI / HTH.

Daniel

(jigged and waiting for TIG welding)
(built-up)
(close-up of boom tubes)
(with a full touring load)

Last edited by dsmyers; 08-10-09 at 05:01 PM.
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Old 08-11-09, 04:01 PM   #6
storunner13
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But has anyone tried this with two road frames with 4130?
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Old 08-12-09, 05:32 PM   #7
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What a fantastic job!
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Old 08-13-09, 04:16 PM   #8
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Yes you can do that. Moly would braze-up quite nicely. It was how the first tandems were made way back when too. I'm really impressed with the above photos of the home-made bike. I honestly think I'd rather have a bike built like that, then buy a factory made job.
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