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Bike completed: not yet

sketch of back to back bike
quick sketch

I've been thinking about back to back stuff since CANC2 when the problems with the tandem trike became obvious. Mostly the weight distribution (too much on the rear wheel).

So I'm thinking about how a space frame B2B bike could work. Looking at the web, Legs Larry's tandem page is good. The idea is to avoid the big beam down the middle approach like MicWic or Ostrad, instead aiming for the Flevo Rug-an-Rug style, possibly even down to the moving bottom bracket steering. But more upright than that, to make it shorter and easier to store. The space frame might even make that easier, if I can make it demountable. Ideally, of course, into a bunch of tubes with numbers on them - to assemble bicycle, join points 1,2 and 3 using bolt x. Now join 2,4,5 using bolt y. Repeat...

The sketch above shows the bare outline that I came up with in two minutes with the CAD package. I'm thinking that if I use 16mm or 19mm 0.9 wall CroMo for the real version it should be fairly strong and light, but still carry a reasonable amount. I'm going to try for a more or less standard SWB front end. The space frame could make it interesting, I'm thinking I may end up with two diagonal braces from the battom of the mid section that come to a short vertical brace parallel to the headset but level with the front of the seat, just to keep the bike narrow around the headset. But that reduces torsional rigidity, so I'll have to do more detailed drawings to know whether it can work.

I'm tempted to make this a moving bottom bracket bike, but the difficulty of riding hte ones I've seen puts me off. I fear that it might be hard to recruit captains with that setup, which kind of defeats the purpose. Perhaps as a separate project...

I think the first step will be to obtain a couple of BMX's and build something out of cheap steel and old bike frames, like Tall Bike.