Detachable Tandem - Page 1 of 5
Tandem cycling is great fun for big kids and adults, but if the smaller ones want to come a long for a ride they will not be able to reach the pedals due to the size of the frame on an adult tandem bike. You could have the kids tag along on their own pint-sized bicycles, but this also may be a problem because of their lack of speed or ability to make the long journey.
The detachable Tandem solves the problem for the smaller bicycle enthusiast in the family by allowing them to "tag" along, yet still participate by doing some of the work. This simple "half-bike" attaches to a special X/Y joint on the main bicycle's seat post allowing the unit to move up and down, left and right, but not allowing the unit to tilt side-to-side and fall over. Because of this, the rider on the detachable can feel like he or she is riding a regular bicycle, yet there is stability.
With a 20 inch wheel on the rear of the Detachable Tandem, it would be quite easy for a kid to pull his or her own weight as part of the riding team, although you can't expect the young ones to keep up the pace when you are blasting around at 30 km/hr. If you do happen to "out run" the usable gear range of the Detachable, the rider only has to stop pedaling and glide until the speed returns to normal, since the pedals are fully independent of yours.
This Detachable Tandem can be built in a day or two from common parts that you likely already have in your "scrap pile". The main part of the project will require a kid's bicycle frame and rear wheel that fits the frame like the one shown here. There are many different sizes of kid's bikes with wheels from 12 inches to 24 inches, but for best results use a wheel no smaller than 20 inches. If you choose a wheel smaller than 20 inches for the Detachable Tandem, then the child riding it would never be able to contribute any pedaling power due to the incredible speed he or she would have to rotate the cranks in order to match your pedaling speed.
Once you have your donor frame and rear wheel, put it away for now because we will first create the most important part of this project, the swivel joint. This swivel is the key to this project, and has to allow the detachable to move up and down as well as left and right but not sideways. This may seem a little confusing at first, but think of the reasons behind this design. If the Detachable could not move up and down, it would either be lifted off the ground if you rode over a large steep hill or snap right off at the joint. You could not have all three wheels on the ground at the same time unless one of them could move up and down to conform to the slope in the grade. The Detachable also has to move left and right so the main bike can steer. This system works the same way as a truck pulling a trailer, no mystery there.
Ok, now you may be wondering - why not just use a ball joint or something similar to a trailer hitch then? Well, at first this would seem logical because it would allow any type of motion at the joint including up, down, left and right. The problem is that it would also allow the Detachable to move side-to-side, or roll which would allow it to fall over, even if the main bike was standing straight. Since the Detachable has no front wheel or steering, it cannot balance independently of the main bike and would fall over and be dragged along. Imagine a truck pulling a trailer with only one wheel - not good.
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You can build it yourself from our easy to follow DIY plans!