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University of the Study of Udine Velo Vision Top - Informatics x Sport Ares Group
 

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.  

Raffaele durante le prove con L'universita di Udine
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 v2, where Rr is the rolling resistance and k x v2 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.

 

Prelievo sanguigno
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 VO2, expressed in J x s-1) to the speed of progression 
(v, m x s-1).
In turn, oxygen consumption (VO2, 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 e-mail:
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 VO2 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).