A Separable Tandem Bicycle (from an Existing Tandem Bike)

Tandem bicycles are efficient (20 km/h is easily reachable), enjoyable (both front/back seats have pros/cons) and allow two cyclists to arrive at the exact same time!

The downside is that you can not transport it. It is very long (about 2,40m) and no public transportation will accept a tandem: bicycle racks are standardized for "solo bikes". Once made separable a tandem can travel everywhere as two luggage.

Foldable bicycles are older than what you can guess (see that military bicycle from 1898 or this modular triple/quadruple bike from 1920). More modern (and available for sale) tandem bikes can be handled in a small plane or in a train.

The most common separable tandem that one can found are made from S&S couplers, those have been invented in the 90s by an enthusiastic cyclist who wanted to bring his bike on a Mediterranean cruise (and was the owner of a mechanic workshop). This system looks pretty neat but is expensive and is not sold to individuals. Other systems exist, including:

• the actual Ritchey system
• an old René Herse system
• a system with clamps, very good but for narrower tubes
• a nice DIY coupler that requires a lots of equipment
• a scaring (but proven) DIY system found on... Instructables!

Well, finally, there was also another way to do it.

• A Tandem Bicycle that has a Steel Frame
• Cable Splitter for Inner Brake Wire (x2 or x3)
• Cable Splitter for Gear Inner Wire (x3)
• Roll Cage Tube Coupler of different sizes, in this specific case:
• ref. 39130225 (25x1,5 mm)
• ref. 39130230 (30x2,0 mm)
• ref. 39130235 (35x2,0 mm)
• Weldable slotted stop for cable management (Silva Art 111 slotted stop, ID 6,3 mm - x4)
• Extra bicycle hardware to be welded in case you want to travel with :
• Rear Pannier Boss, Silva Art 294 - x2
• Bottle Cage Bosses, Silva Art. 475 (M5 bottle cage boss 9 mm x4) and Silva Art. 476 (M5 bottle cage boss 10 mm - x4)
• Weldable consumable:
• Solder Flux Powder
• SIF Bronze Rod No 2 - x5
• 2 big bags for transportation

Again, I insist, it has to be a *steel* frame (check it with a magnet, or spot rusted parts) since you are going to weld parts on it. Aluminum, Titanium (one can dream), Carbon Fiber, Bamboo or anything else is from my point of view out of question.

This one is an old Orbita, Portuguese-made in the 90s.

Here are the basic parts used. One can find :

• Tube Couplers, those are used in rally cars, for splitting the roll cage when you want to access the engine. So here is the tricky part: you have to guess the inner diameters of the tube you are going to cut. On this basic tandem bicycle, the tubes have constant thickness all along the length. On expensive bikes, it is buttered. Welding with a blowtorch, with bronze rods, is quite forgiving. But still, the coupler should not float in the tubes.
• Cables Couplers, required for the rear brake and for the gears. These smart tiny things allows you to split the cables in two parts. Be careful though: it means that you have to see the cable (you do not want to split the sheaths).
• Soldering flux powder and bronze rods. The tube couplers are going to be welded with a blowtorch (though it *might* be done with arc welding but it is much, much more tricky since the bicycle tubes are pretty thin - I would clearly *not* recommend doing it that way).

Saw time! As it is common to say in wood workshop: Think twice, cut once.

The two half-frames should be more or less of equal lengths including fork (not easy to separate), mudguards, racks… Check out the regulation of the transport system you want your tandem to travel with, use a ruler, do some drawings, print models… Take your time!

In this case, some paper models have been done: those have the length of the couplers and were glued to the frame. It is a good way to see what's going to happen. Also it helps cutting straight (yes that has been done with a metal saw, by hand).

Please note that the tube couplers are aligned on a left/right position. As the tubes that have been cut are not parallel, it would be impossible to separate the 2 parts by "lifting" the rear part. So the tube couplers are set horizontally in order to separate the 2 parts by sliding them on a left/right movement.

See the picture with frame with and without coupler? Well look at the pairs of black screws on the bottom picture: that does not operate. Couplers are well set on the following step: screws are looking up and thus will allow the separation by this left/right slide.

A strap has been used, it helps to maintain all the parts together but be very careful with the alignment: if the cuts are not perfect, tightening the straps will lead to misalignment. Use a ruler to check that the frame follows a straight line.

The tube couplers position is critical, you will have to clamp and/or tack those. Check if the 2 parts of the frame are sliding correctly before full welding.

So, the brake and gear couplers are coupling the cables, not the sheaths! See the picture: on the top one can see the original Sheath Guide. Below it is the new Brake Stop. This means that before transformation, a sheath was going over the tube coupler. Now, this new Brake Stop means that there is an "open air brake cable" over the tube and it will be split thanks to a cable coupler.

Fun fact: brake cables of tandem bicycles are specific (because extra-long). With these cable couplers you will use standard cables (just two of them are required for each break/gear).

When soldering, you are damaging the painting so it makes sense to add all your needs/desires before cleaning and painting the whole frame again. Extra bosses for a rear + fork racks and mudguards have been added. Also extra bottle cage bosses for putting stuff have been welded.

Take your time to imagine, list, draw whatever is required for a future trip, should it be for commuting or for longer journeys…

Everything welded? Hum, OK it is time to set everything back on the frame, drive a few kilometers. Is everything operating the right way? Do not hesitate to do a little extra, ride down the sidewalks full speed, brake strongly… Well, now is time to disassemble everything from the frame!

You'll find a lot of good tutorials on painting a bicycle frame. Just be extra careful with cleaning the rust and protecting with paper and tape the unpainted zones (where the ball bearings are set, tapping screws, inner tubes of the seat posts)…

The downside is that, homemade, you will never reach the quality of the original paint (even from low quality bikes). I would advise you to find a professional to handle it (this is not very expensive finally).

Finding an appropriate bag is not that easy and finally depends of your plans. There are not so many reasons to put your split tandem into bags. Usually on trains, it is fine to split it and store the 2 parts in the adequate compartment.

...and enjoy the View!