my tandem -recumbent for loaded touring
Carbon monocoque, positive laminated on PU-foam core
Front: central in the headset (a bit like Canondale, but not quite) / Rear:
Front 406-32 / rear 559-40
Just under 3 meters
Ca. 26 kg
Length of riders: Front 170 cm to
200 cm / rear 160 cm to 195 cm
2 ortlieb back-panniers on the rear lugage-carrier / two cilinder-kanoobags
below rear seat
Some pictures of the animal,
and of her birth
Click on the pictures for a
Touring in France(74 kB)
A side view (36 kB)
Front part of the core
Rear part of the core
Detail of the front suspension
On of the most common problems on tandems are broken
spokes. Tandems exert huge loads that bicycle wheels are not designed for.
So I decided to make both rear and front suspension to avoid spoke problems.
Rear is a simple swing arm. To avoid unequal spoke tensions the rear wheel
is not dished, and the hub is set at a little offset from the centreline
of the bike to compensate. The front suspension is the most difficult part
of this bicycle.
The frame is extremely stiff. I believe this
to be a requirement for safe high-speed driving. Handling is excellent:
very light shimmying around 45 km/h, at higher speeds absolutely straight.
One hand driving possible up to 75 km/h (may be even faster, but my courage
does not allow it).
Brakes are a problem on longer downhills. Due
to the high loaded mass (about 220 kg) the rims get very hot. You have
to brake as little as possible, and to stop every few km to allow the rims
to cool. With these brakes I do not go into larger mountain ranges like
the alpes. Fitting a good disk brake could solve the problem, and I will
try this in the future. If anybody has experience with disk-brakes: please
Construction of the front
Around the stem of a conventional fork a stainless
steel tube is bonded with epoxy. This tube can move vertically in two POM
bearings that are mounted in an aluminium intermediate tube. The intermediate
tube is mounted in the frame by means of two industrial thin section ball
bearings. These bearings can not withstand large axial loads, so for the
vertical movement of the fork a simple but ingenious construction was designed:
A short stainless steel swing arm is mounted
to the underside of the frame by means of a ball link. The other side of
the arm ends exactly in the middle between the fork legs. At this side
a thin stainless steel wire is mounted (bought in a yachting shop). This
wire goes upwards trough the fork stem and is connected to the top of the
stem. The wire allows rotation of the fork, so the steering is not influenced.
For the suspension a rubber element is mounted between the frame and the
swing arm. This element restricts the upward movement of the arm, and hence
also the upward movement of the fork.
The POM bearings have to be fabricated to close
tolerances, and provide a little damping. This suspension is simple yet
effective, and very durable, even under the high (tandem) loads. I hope
to provide a sketch soon, for better understanding.
I tried to use the POM bearings also for the
rotation of the fork, however this arrangement had to much friction, and
the handling of the machine was horrible.
And the name of the machine
After a horse from a Dutch childres book. The horse
was so extremely long that two wheels were mounted in the middle under
her belly, and a whole family could ride her together.
Last changes: 17-3-'98
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