TANDEM – A BICYCLE BUILT FOR TWO

TANDEM - A BICYCLE BUILT FOR TWOFor many years I am a regular subscriber of “M-A” and find in it many interesting and necessary. I hope that my experience will be useful to other readers: I would like to share my thoughts and practical recommendations regarding the manufacture and operation of a tandem bike. A car I made on their own five years ago and drove it for thousands of kilometers.

So, first about the merits of double bike. First, is the ability to drive with the high speed comparable to the speed achieved racing bikes. Secondly, tandem is convenient when traveling two different people: you can rotate the pedal with usual force and automatically a stronger “pull” is weak. This is one of the advantages to recommend these bikes for tourism, especially family. And the presence of lead in the two holding the control in your hands, reduces risk and psychological tension when driving on roads with heavy traffic.

 
But “there is no free cakes”: a tandem has some disadvantages. It’s lower maneuverability, greater stopping distances, less maneuverability on uneven, hilly terrain, more difficult riding alone because of the greater weight of an articulated tion of the machine. So, before you take up the tools and to manufacture a “long” bike, think about the opportunities of its operation, the available space for storage. If you think that the tandem you need, I suggest become more familiar with my option, although solutions may be many.
The frame of my bike, as seen in the photos, welded from two frames sport bike “Sputnik”. Its dimensions allow it to enter into a standard cargo lift, removing the wheels, and the passenger without a front wheel. The use of frames road bike eliminates the possibility of using a passenger Elevator. Also suggest not to purchase the frame from the racing cars as they definitely will have some difficulty with the placement of wheels of the type 40х622. And since the test load is quite high, it is advisable to put a fork with thicker feathers.
 
Layout home-made tandem.
The layout of a homemade tandem.
 
To make the frame in various ways. Based on their capabilities, I chose the following. From the front frame is finally a chain fork. The second rear fork of the frame is left without any changes (this is, incidentally, one of the advantages, as necessary — for example, if there is a catastrophic failure in the long journey — with a hacksaw just a half hour to redo a tandem in the usual alone).
 
Now you need to saw across the seat the front frame tube at a distance of 100 mm from the top and raise the resulting to the right and to the left. Then on the lower part of the “dressed” steering column rear frame, and the inner cavity of the seat tube is inserted into the bougie (you can use the tube from the saddle), the flattened parts fit together and scald by electric welding. From a third frame (optional; any broken, scrap) shall be cut the lower pipe with the half of the carriage and is inserted between the carriages of the front and rear frames. Front mount is overlapping with the fixing of the temporary technological M6 bolts, and the rear by welding; and then obvalivautsya connection on the front of the carriage bolts are removed. Frame ready. For this design I went on any roads, and the weight of passengers was close to 200 kg — there was no damage.
 
Assembling the frame of the tandem
The Assembly of the frame of the tandem:
1 — rear frame 2 and front frame 3 — additional tie between the carriages of the front and rear frames.

Multiple gears for the tandem is highly desirable. Although complicated by the kinematics of the structure, it should be reconciled, since the use of different gear ratios pays off on a variety of terrain from plains and mountain roads.
 
Torque on the rear wheel is transmitted through two chain drives: one between the pedal sprockets with gear ratio equal to one, and the second standard, from Sputnik. Chain can be placed on one or different sides of the axis of the bike. Many sources recommended the second method as the most simple in execution. I strongly advise not to do it due to the fact that the margin of safety of the Bicycle parts is small, and the possible need to use solutions that allow to increase the load on the standard nodes. When placing the same circuits with different sides of the load on the rear of the carriage is multiplying, therefore, the shaft, the bearings and the cups are very easily damaged. Added to this is the fact that on the left side are the “right” rods and all the pedals except the rear right, standing on their “home” and constantly strive to get out.
 
Kinematic diagram of the drive tandem
Kinematic diagram of the drive tandem:
1 — the rear sprocket Assembly (from the “Satellite” or “Start-highway”), 2 — back circuit, 3 — rear sprocket front-wheel-drive (Z=40), 4 — rear sprocket (Z=51), 5 — idler roller, 6 — front chain, 7 — front sprocket (Z=40).
 
Installing rear wheel.
Installing rear wheel.
 
One, right, side to put the chains harder, but in the future there will be no problems. Technically it’s done. On the shaft of the front carriage propisyvaetsya file the groove for the wedge so that it was possible to move the connecting rod to the left. 40-bevel sprocket is attached to a cropped centre from 50-bevel sprocket, and the additional washers also move it as far as possible to the left.
 
To the rear of the carriage shaft is selected with the greatest departure to the right, repeated the same procedure with the cutting of a groove on the shaft to move it as far right as possible, but in this case it helps not much, as the groove is so close to the edge. Another possibility is to shift the shaft — rasp the side of the wedge.
 
To circuit do not touch each other, the thickness of distance washers between the sprockets in a conventional Assembly increases. If the rear chain will cling to the plug, the latter can gently make a small indentation.
 
Prolonged use of the tandem showed that neither synchronous nor perpendicular installation of the connecting rod does not provide the desired uniformity of movement. It is necessary to experimentally find the optimal angle between them: this will provide movement without jerks and convenience when landing and starting.
 
The tension of the front chain by using a roller from the old caliper. It is attached to the frame by a clamp. Since the spring parallelogram with the caliper removed and retained only the tension — roller self-aligning in the transverse direction.
 
Installing the roller chain tension front drive.
Install roller chain tension front drive.
 
Front wheel and seat have no special features: uses normal. The rear wheel is homemade from a pipe from a broken bike frame (it’s light and durable). Mounted the wheel with the standard clamp and long bolt to the tube front of the seat. Additional ease of use creates eccentric clip from a folding bike on the tube back seat — this allows you to adjust its height, which happens often enough.
 
Back leading, the wheel is going to be based on aluminum rim from a road bike, and the sleeve is taken from the “Start-highway” with “Paterikon” 13-15-17-19-21 or staff from Sputnik (in the latter case, the smallest sprocket has 14 teeth, therefore, the maximum speed will be somewhat less). The front wheel also better equip rim of rectangular cross section from a road bike because “sotnikovskoye” is rather weak. In a pinch you can “put on” their road “rubber” — this will soften the blows and reduce the probability of “breakthroughs” to the rims.
It should be remembered that on the rear wheel have a large load, and on my tandem had to replace two rims and two tires, front is still fine. Therefore, it is necessary to immediately develop a neat style of riding, and regularly watch your blood pressure — it should be 2…2.5 kg/cm2 to 3…3.5 kg/cm2. It is important not to forget the constant and strong tension on the spokes. By following these recommendations, you can extend the life of the wheels.
 
Great value on a double bike has the reliability of the brake system. To improve when using beztormoznoy bushings and brakes as tick-borne rims desirable notches, increasing the coefficient of friction.
 
A sporty version of the tandem can be equipped tulipani all the pedals. However, for everyday or travel use to do it should not — enough tulipson only on the front pedals, as not all companions know how to use them; in addition, when riding alone, they cling to the ground.
 
To rear mud flap does not interfere with roll tandem in the Elevator, he slightly clipped. It’s mounted at the rear of the trunk.
 
A. LATKIN

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