The resistance experienced by a cyclist consists of three components:
Transmission resistance.
This is the resistance that is caused by the mechanical parts
of the bicycle which convert power into speed. These mechanical
parts include the chain, chain wheels, sprocket wheels and ball
bearings. Well-greased ball bearings and a well-oiled chain
only yield a minimum of resistance. Between 3% and 5% of the
capacity of the cyclist is used up by transmission resistance.
The transmission resistance remains constant when the speed
increases.
Roll resistance.
This is the resistance which arises as a result of deformation
of the tires. Deformation of tires occurs as a result of the
weight of both the cyclist and the bicycle and as a result of
irregularities in the road surface. This deformation costs energy
which does not return into the system. Linearly the roll resistance
increases slightly when the speed increases. At a speed of 44
km/hour on an even road and wind still conditions, the roll
resistance of an average person amounts to 12% of the power
yielded.
Air resistance.
This is the most important type of resistance that a cyclist
has to overcome because air resistance increases as to square
of the velocity. In the above-mentioned example the air resistance
amounts to 88%. The diagram, below, assumes a cyclist weighing
75 kilograms, a body surface of 1.8 square meters, 0.45 square
meters of frontal surface in a standing-up position and a bicycle
weighing 9 kilograms. The formula for calculating the air resistance
is:
W = p/2.Cw.A.V²
P = airdensity
Cw = drag coefficient
A = frontalarea
V = speed
RESISTANCE
The resistance experienced by a cyclist consists of three components:
Frictional resistance.
This resistance occurs when layers of air pass each other at
different speeds and thus influence each other. The air immediately
surrounding the cyclist moves past the environmental air, which
results in resistance
Shape resistance
This is the most important kind of resistance. The air in front
of the cyclist is pressed together, but behind the cyclist the
air is more or less sucked away. This leads to a difference
of pressure in front of the cyclist and behind him, which in
turn leads to an opposing force.
The extent of resistance is determined by the size of the frontal
surface which is perpendicular to the direction of movement
and the shape of the body, also referred to as streamline. This
is the measurement that indicates to which extent the air is
enabled to glide gradually past the cyclist and his bicycle.
Wind tunnel experiments have shown that the cyclist is responsible
for 75% of the air resistance, and the bicycle for 25%. Some
researchers assert that a streamlining of the bicycle is only
meaningful at speeds of more than 56 km/hour.
It is obvious that a good aerodynamic position on the bicycle
depends on many factors (such as speed) and can differ from
individual to individual. Certainly for riding a time trial
or the world hour record, an individual assessment of the position
on the bicycle is of vital importance. As a rule, a horizontal
position of the torso is the most advantageous position when
it comes to matters of air resistance. This implies that the
upper part of the hip and the acromion must be in a horizontal
line. At a deviation of only 10 degrees upwards, the speed decreases
with an average of appr. 1 km/hour, or 2.5% (Van Ingen Schenau
1985).
From High-tech Cycling (1966). Although this diagram is in principle
a correct reflection of the resistance, it seems that the power
output is relatively high