Energy consumption during cycling
Speed
km/hr
Cycling time t
min
Weight of cyclist
kg
Weight of the bicycle
kg
Rolling resistance coefficient C
r
-
Air resistance coefficient C
w
-
Frontal surface area A
f
m
2
Uphill slope k
%
C
w
·
A
f
m
2
Air resistance F
air
=
½
ρ v
2
C
w
A
f
N
Rolling resistance F
rol
= m
tot
g C
r
N
Force for climbing F
climb
= m
tot
g sinφ
N
Energy per minute E = F
tot
v t, t=60 s
kJ/min
kJ/min
Energy "burned" per minute
1)
kJ/min
kcal/min
Efficiency of the cyclist
%
Driving power P = F v
W
Energy delivered E = P t
kJ
kcal
Energy consumed (burned)
1)
kJ
kcal
1)
The energy burned is approached using reference tables of different web sites like
source1
. Reference values are correlated to the energy delivered by cycling.
2)
The dimension kcal (1 kcal=4.19 kJ) is the old dimension for Joules.
3)
The energy delivered by the muscles is small compared to the energy burned, only 12.5% with a cycling speed of 20 km/h and 20% at 30 km/hr.
4)
In comparison, the efficiency of a large electric powered motor is about 90%, of a diesel engine 40% and a petrol engine 25%. In the calculation of the efficiency of an electric powered motor one should consider the efficiency of power stations that transform fossil fuels in electricity. The efficiency of a coal power plant is about 40%, that of a gas power plant 45%. This actually reduces the efficiency of an electric powered motor to 0.45 0.9 = 40%, not more than that of a diesel engine.
www.engineering-abc.com