






DEPARTMENT
OF BIOMEDICAL SCIENCE AND TECHNOLOGY  UNIVERSITY OF
UDINE 
(Italy) 

 The
collaboration between the Ares Group and the Department of Biomedical
Sciences of the University of Udine started in October 1996 when
scientific tests were undertaken in order to determine the mechanical
efficiency of riding the Karbyk (“Race” version).
 The
collaboration was continued in 1999 when the “Road” version
of the Karbyk was tested too.

 The
two series of tests were performed with the same methods and procedures to allow a quantitative evaluation of the technical improvements brought
about by the Ares Group in the mean time.
 Our
evaluation was aimed determine to the drag coefficient and the rolling
resistance of the two versions of the Karbyk.



 To
do so mechanical power (p, W), at constant sub
maximal speeds (from 5 to 9 m x s^{1}), by means of a
strain gauge system (Powermeter  made in Germany by SRM Company) mounted
on the chain ring of the Karbyk.
 The
external mechanical energy spent per unit of distance (w, J x m^{1})
to proceed at a given speed (v, m x s^{1}) was
calculated from the ratio: p / v.
 The
relationship between w and the square of v is described by: w
= Rr + k x v^{2}, where Rr is the rolling resistance
and k x v^{2} represents the work done to overcome drag.
 The
coefficient of rolling resistance (Cr) was obtained from Rr = Cr
x M x g, where M x g is the overall weight (subject plus Karbyk).
 The
constant k is proportional to the air density (r) ,
to the frontal area (A) and to the drag coefficient (Cx)
: k = 0,5 x A x r x Cx.
 Cx
was therefore calculated on the basis of the measured values of A, r
and k.
 The
rolling resistance coefficient (Cr) was found to be about twice
that of a traditional racing bicycle (but with two wheels) for the “Race
1996” version of the Karbyk, whereas the Cr of the “Road
1999” version was found to be about 20% lower than of the previous
version.
 This
improvement was obtained with a reduction of the tires thickness and with
an increase in their inflation pressure.
 This
improvement is remarkable even because the “Road 1999” version is
heavier (about 3 kg) than the “Race 1996” one.
 The
drag coefficient (Cx) was found to be about 30% higher than that
measured on traditional bike (with the subject in a racing posture) and to
be only slightly lower in the Road version (about 5%) as respect with the
Race one.
 This
improvement was obtained by fairing the tires and part of the chassis.


 The
energy cost (C) of riding the Karbyk was also measured
(“Road 1999” version only) from the ratio of metabolic power
expenditure above rest (net VO_{2}, expressed in J x s^{1})
to the speed of progression
 (v, m x s^{1}).


 In
turn, oxygen consumption (VO_{2}, l x min^{1})
was measured by means of a telemetric system (K4RQ, made in Italy by
Cosmed Company).
 Net
mechanical efficiency was then calculated from the ratio of w
(J x m^{1}) to
C (J x m^{1}) and found to be comparable to
that of a traditional racing bike.
 The
collaboration with the University of Udine is only at his initial stage:
the original idea is to prove the potential of this human powered vehicle
not only for sports activities but also as an alternative solution to
urban transport and traffic jams.
 For
further information contact Dr. Paola Zamparo at email:
 PZamparo@makek.dstb.uniud.it


 Typical
traces of Speed, Power and Cadence as measured by means of the
Powermeter (made by SRM in Germany) in one subject riding the Karbyk
“Road 1999” version at 18 and 20 km/h.
 The
subjects were asked to cover there and back a track 1 km long at constant
speed and to increase their speed by 2 km/h every complete cycle of 2 km.


 The
average values of power, speed and cadence were calculated from the values
measured while covering the 2 km distance, run along at the same speed,
disregarding the values corresponding to the deceleration and acceleration
phases that occurred every 1 km when the subjects had to invert the
direction of movement.
 This
allowed us to compensate for the effects of wind speed and inclination of
the terrain (if any).


 Values
of Speed and of Oxygen uptake (measured by means of the K4,
made in Italy by Cosmed Company) as obtained in one subject riding the
Karbyk “Road 1999” at 18 and 20 km/h.
 Average
values of VO_{2} were calculated as described in the legend of
Fig. 1 for power, speed and cadence.
 The
net energy cost of riding the Karbyk was obtained from the ratio between
the average values of net oxygen uptake and the corresponding average
values of speed (see text for details).




