MassiveD

Anyone with tips on tandem design? I am starting from scratch, and the front and rear triangles seem fairly standard, but the middle section which incorporates the added room for the stoker bars is a bit of a mystery. Ftwelder had a nice build, but I couldn't read the dimentions on his drawing, or relate them to the underlying frame designs. I'm not going to be welding some existing frames together.

Live Wire 

Of course a lot depends on the intened use of the bike- racing, touring, marriage wrecking, etc.
I've only been involved with building one tandem (for track racing) but I did a whole lot of research going into that project and I found a good general rule of thumb is to keep the boom tube at 70cm or a little longer. That allows for accomodating a wider range of riders while keeping a decent nose-to-butt distance for the stoker.

Andrew R Stewart 

The obvious first choice is to copy an existing design. Or at least taking solid cues from a few. Having over 35,000 miles on a couple of tandems and seeing a LOT more up close I like the CoMotion design style for steering geometry, especially for experienced tandem teams. The front triangle is almost like the captain's single, maybe a tad shorter in top tube. The stoker's mid section can't be too long by some opinions. One thing to consider is the BB c-c length, timing chain adjustment/ring size, eccentric range relationship. There's boom tube length steps that work better then the lengths between the steps. For the rear triangle, again longer is better. Tandems stretch gear range limits often and with the drivetrain so far away from the captain the likelihood of cross chaining is much stronger. A few more CMs of chainstay won't make much difference in the handling but might make the stoker happier... Remember to keep the stand over clearance large. Andy.

MassiveD

Thanks for the ideas. How does the steering geometry of a Tandem differ from other bikes? Longer wheel base, but is there anything unusual about the way they are arranged up front.

The service I have in mind is a front end 58, and the rear end to suit my various girls, three daughters and my wife. one at a time There are times when it would be fun to ride one together, and there are carpooling type situations where you need to ride the ride to one or the other of them for the pick-up. Secondary capability would be for a little touring.

MassiveD

Also be interested in standard tubes.

Andrew R Stewart 

There are two competing steering design styles for tandems. The Santana/Burley one is that stoker steer potential is a bad thing and the trail should be less to reduce this. The CoMotion/Calfee idea is to increase the trail so the handling is more "single like" at the expense of greater stoker steer. Also the larger inertia of two riders make any steering geometry feel slower then a single bike's. Have you measured the geometry of a number of tandems yet?

At the shop that i worked at for 7 years that sold all these brands we found that the first tandem was usually the Santana/Burley design. But the second tandem (the upgrade...) was usually the CM/C style. I always thought that the more experienced team had learned to reduce stoker steer by their behavior while getting use to the first tandem.Then when moving onto the next one wanted a more reactively handling tandem.

As to tubing: it's hard to not make a tandem too stiff, especially if touring weight is to be carried. So big tube diameters rule. The walls get pretty thin on the sport bikes to keep the weight down but stiffer is generally better. At one time Santana use to sell there tube sets to privet builders. I would stay away from single bike specs at all costs. Andy.

ftwelder

I can provide you with my drawings if you want them. I sort of "came up" with them and don't know how they will work. It's great to hear from someone who sold tandems and has tried different ones. Builders don't seem to want to talk about their designs too much.

PM me your email address and ill send you a PDF if you like.

mine is still at the painters. I told him "no hurry". 'wrong thing to say to a painter (or frame builder).