It's now my second instructables and I present here my new tandem !
New tandem because I have already build one, but really less successful than this one.
The idea was then to improve the first version by correcting problems.
The first tandem was built with two road frames (I took them because of their big sizes). You have the picture for this construction. In my defense, it was my first welds and my first construction. Looking at the mistakes :
* bad welds : because of thin tube (road bikes) and experiences...
-> I took for the new tandem mountain bikes and I have, I think, more experience about welding
* because of the weld, the rear bottom bracket was deformed and it was impossible to correct adjust cranks.
-> I weld now with the mechanism inside, this not deforms anymore.
* bad steering : it was hard to turn at low speed, lack of maneuverability
-> because of the angle of the head tube and maybe the handlebar...
* Not enough space for the passenger
-> I had cut the head tube and directly welded it to the seat tube of the first tube. Here, I keep only the rear triangle of the bike and adjust my tubes to keep enough space.
After the first construction, the tandem stayed few months in the courtyard and recently we used it again. Bad experience. We also had the opportunity to test a real tandem, woh! Not the same feelings.
And here we go, a new tandem, pretty nice, works well, ... :)
This time I considered equipment and many things before welding as transmission, size, ...
I take my inspiration in Lapierre Tandem. (http://www.cycles-lapierre.fr/2015/velos-route-tandem/tandem-touring)
You can have angles, sizes and it was very helpful !
Lucky, I found the first bike with same size of the model. The final frame is very similar to the model but I don't checked angles. Only TT size (on the picture).
When I had everything (bikes, tubes, equipment), I started to build the frame.
Step 1: Build the Frame
First of all, cut the rear triangle of your future front bike and cut the front for the second one.
As explain, this tandem has been build without chain tension intentionally, the first main tube (join the two bottom bracket ) has then been choose and cut for the chain. I have chosen before pedal, of course.
The tandem, for the binding chain, has two 42 teeth chain wings. I adjusted the size of the chain and the length of the main tube consequently.
I welded first the main tube between the two bottom bracket. Of course, you have to check your alignment, the two frames have to be aligned (in the same plane) but also at the same height.
I don't have a JIG so I manage as I can with boxes, wood,...
In theory, bottom brackets have to be at 27cm to the ground. In theory only ;) Good luck !
After welding the main tube, checking the alignment, I replaced the chain and test the strain. The second tube permits also to modify this strain : you can modify the seat tube angle with the ground and this impact the strain chain.
When this is welded, you have your tandem !
After mounting the frame on wheels, our first impression was: "it's too small"!
But no, with seats, handlebars, it's absolutely not !
Because we wanted to adhere at our Lapierre tandem model, and for stiffness, I had the transverse tube between the head tube and the bottom bracket.
Step 2: Add Equipement
After putting the wheels (26"), the transmission, the seats, the handlebars, I needed to wire the bike for gear and brakes.
I have 3 chain rings, 8 gears.
By chance, I only needed to extend one cable for the rear derailleur. The tow others (rear brake and front derailleur) are just but enough long ! I extend the cable with two bolt simply. This works.
To do it proper, I cut cables guides from old bikes and welded it to the frame.
I have done the same for inserts (to install a back rack).
After test, the stress chain was correct but I derailed once. Since, I have change the chain (to a new one), and it's perfect! (It's not the best option, I know, but when it will be a problem I could do the same, again and again... :)).
For the second handle bar, I took two stems, I cut them and I welded them with a main tube.
The first stem fixes the whole thing to the seat tube, the second one fixes the handlebar. I used two tubes for the main part : one inside the other to make it adjustable. I can if I want extend the tube and have a longer stem.
Step 3: Test and Dismount, Paint It
Héhé! Ready for the first test ? It was really nice ! You have enough space at the back and front place, the steering is really better than the previous one and we can go fast.
Now, the least interesting part .... dismount it, everything !, unpainted... and repaint it nicely!
Step 4: Final Version, Ready for the Road !
Tested and approved !
Let's go !
Edit : Tested today during the whole day, many hills, every thing ok ! Just a thing : I have to improve the brake system for the downhills.