Luke's Little Tandem for Mary and Sophie
Luke Breen brought in his unpainted but basically complete tandem built for wife Mary and his oldest daughter Sophie (if he can get it done before she outgrows it!). It is intended mostly for daily running around, with touring as an option too. This is his fifth bike, and it was by far the hardest one yet and the one that managed to stump him occasionally. The frame was sort-of done and brought to a meeting almost a year ago, but the "ten hours or so" of work to finish it stretched out because of a few seriously tricky areas.

One change was to make it rideable for himself, if at all possible, so it now has a longer boom and more seat travel. He may need to make a second boom for himself to get enough extension, or a double telescoping boom (an idea he is not wild about). He also wants to swap the middle chainrings so the primary chain will be on the outside and thus easy to swap out completely so he won't have to be constantly fiddling with adding or removing greasy links. He received several suggestions about a seat height adjuster so he won't conflict with the stokers feet when he is riding it with the seat far back and was excited to get home and implement one of them.

One problem was the HUGE flange and bolts he originally planned to use as a joint for breaking the bike down for travel (it will probably be going to New Zealand next winter for their semi-regular bike tour there). He ended up trashing that idea and going to S&S couplings, but that required sleeving down the main tube from 2.2 inches to 2.0 inches, the largest size for S&S couplings. This in turn led him to add a bracing tube below the main tube regain stiffness lost with the reduced main tube size. That tube also has an S&S coupling. Cable splitters complete the traveling arrangements.

The flange scheme is certainly workable, as a much smaller version is used to allow the Penninger trikes to separate. However when Luke originally installed the flanges, about a year ago, his only joining skill was fillet brazing. The fillets encroached on the area where the bolt heads and nuts needed to seat. TIG welding, or a slight redesign of the flanges to allow capillary brazing, would make flanges a reasonable alternative to S&S couplings, whenever size, cost, or S&S' policy of not selling to anyone without $1,000,000 worth of liability insurance, makes use of the S&S couplings impractical. Mark S.

He used silver brazing for the sleeves, since that works at lower temps (say 1200 F instead of 1700 F) and it wicks into large but tight joints better. There was some discussion about silver versus bronze brazing, and though silver works at lower temps it cannot be done with a regular propane torch. If you lack Oxy/Acetylene, you need either a MAPP gas torch or a special Turbo Torch propane system that burns hotter than a normal propane torch. He used silver for the S&S couplers because brass and stainless don't bond reliably.

Yet another problem area was the disk brake mounting tabs on the forks and rear stays. He got them to work out OK on only the third try, after downloading a template and instructions from the Magura web site and changing from 1/16 to 1/4 steel sheet.

The front idler is mainly for chainline control, but it also has limited vertical travel for chain tensioning adjustments.

He may look into a Pantour (sp?) front hub with one inch of suspension travel inside the hub (!). These are pretty slick hubs, and better suited to disk brakes since the typical rim braking surface only permits a half inch of travel. Some people assumed that Pantour must be working on a braking system of their own to go with these hubs, but Luke says he doubts that because they are a small mom-and-pop operation. The tandem is finally nearing completion now, and although he had to run the stoker seat way back for Sophie because she is growing like a weed. Fortunately, she has two younger sisters, so anything he builds he will get plenty of use. The tandem will have a trailer mounting stub plus a rack with special mounts for a Burley Piccolo trailerbike.

An area of uncertainty was whether the SRAM 3 x 8/9 hub with disk brake mounts would ever be real or was just vaporware, so he changed to triple chainrings on the intermediate drive so one could take the primary chain and the other two could be used for shifting. A crossover tandem crankset was not a viable option due to cost and the unavailability of short arms for them (he uses 135 mm cranks on the stokers crank). Naturally after making this change the hub did become available, but at a considerable price (about $500 made up in a wheel, though at least that includes two shifters and the rear cluster and derailleur).

The wheels are 305-16 and 406-20, and the front had an unusual 90 psi Schwalbe City Marathon in 305 x 1.9".

Luke discussed the front end design, which he worked out in a specific sequence ala Stonich.

1. Locate the rider, seat height, crank height, backrest angle and shoulder location.

2. Locate the riders hands at the height or width needed to clear the knees, and at a distance from the shoulders, using the method shown at http://bikesmithdesign.com/EvoBars/EvoBarSetup.html

3. Now decide on how much tiller you want. Ideally about 8", but 6" is about all you can get on an SWB, and 10" is acceptable on an LWB.

4. Draw an arc centered on the center of the handgrips, with a radius equal to the desired tiller.

5. Locate the front wheel as close as possible to the cranks without crank/tire or crank/fender interference.

6. Draw a line from a point ½" ahead of the center of the front contact patch, that is tangent to the arc around the hands.

7. This line will be your steering axis, and ½" will be your trail. (If you still believe trail adds stability to a recumbent, we gotta talk. Mark S.)

8. The distance from the axel to the steering axis line will be your rake.

9. Orient the hangrips as shown at http://bikesmithdesign.com/EvoBars/EvoBarSetup.html

(Luke omitted the final step, because it didn't apply in this case.
10. Locate the rear wheel so that it carries 60-70% of the total laden weight of the machine. Mark S.)


Return to November 2002 Meeting Report
Return to MnHPVA Club House