Low Aerodynamic Drag Suit for Cycling
Design and Testing
Live Spurkland, Lars Morten Bardal, Lars Sætran and Luca Oggiano
Norwegian University of Science and Technology, Deparment of Energy and Process Engineering,
K.Hejes vei 2b, 7042 Trondheim, Norway
Keywords: Cycling, Aerodynamics, Wind Tunnel Testing, Garments, Fabric.
Abstract: The focus on garment aerodynamics is increasing in high velocity sports where aerodynamics is crucial such
as cycling, speed skating and alpine skiing. Recently published research show that a low drag suit
manipulating the flow around the body can considerably enhance an athlete’s performance. This project
seeks to improve the Norwegian sportswear manufacturer Trimtex Sport AS’ pro cycling kit using the best
currently available textiles. Changes from the original design are made with the intention of optimizing
fabric zones and seam placement. Drag measurements on cylinder models, cyclists and full-scale
mannequins of the upper and lower body were conducted in the wind tunnel. The reduction in aerodynamic
drag was significant on cylinders, and final power savings of 8 watts due to drag reductions was obtained on
the jersey and 5 watts on the bib shorts for a cyclist racing at 50 km/h.
1 INTRODUCTION
Road cycling is one of the sports with high velocities
and infinitesimal time gaps where marginal gains are
crucial. Aerodynamic drag accounts for as much as
90% of the total resistance to be overcome when
cycling at a normal race pace, 70% of which is
created by the rider (Underwood and Jermy, 2011).
Aerodynamic drag can be expressed as
F
D
= 0.5c
D
ρ
U
2
A
(1)
where C
D
denotes the drag coefficient, ρ the air
density, U the air flow velocity and A the projected
frontal area (White, 2006). Besides optimizing the
rider’s position and suit fit to reduce the frontal area,
it is possible to reduce the total drag by improving
the surface texture of the rider’s clothing and thus
achieve a lower drag coefficient (Underwood, 2012;
Chowdhury et al., 2010).
Research on sport garment aerodynamics has
been progressing since the Nike Swift Spin project
based on the work by Brownlie in the early 2000.
Over 200 fabrics were tested and their final suit
offered a 3,9% reduction in F
D
compared with the
typical 2001 suits worn by competitors (Brownlie,
2009). Some of the most renowned brands of bike
clothing have recently been improving their time
trial suits by full-scale testing of suits with different
textiles in wind tunnels (Baker, 2010; Bioracer,
2014). Even though the results have been good, the
typical textiles used in regular road race cycling
suits on all levels are still smooth and seemingly
made only with focus on fitting and breathability.
However, a low drag cycling kit can give the
necessary advantage in a road race by reducing the
effort needed at a given velocity. The 1989 Tour de
France was won by Greg LeMond by a winning
margin of 8 seconds and by Alberto Contador in
2007 by 23 seconds illustrating the minuscule
margins and the need for perfectionism in the
cycling sport.
It is known that the drag coefficient of bluff
bodies suddenly drops at a certain critical velocity
during transition from laminar to turbulence flow in
the boundary layers (Zdravkovich, 1990) commonly
called the drag crisis. The Reynolds number at
which the drop occurs, the magnitude of the drop
and the subsequent rate of increase in C
D
is highly
dependent on the surface roughness (Achenbach,
1971). A rough surface induces an early transition
but at the same time decreases the drop and
increases the post-critical drag coefficient (Auteuil
et al., 2010). Hence, the flow around a bluff body
can be manipulated by mixing various patches of
textile with different surface morphology to prevent
or delay flow separation at strategic places.
The aim of this work is to find the material and
Spurkland, L., Bardal, L., Sætran, L. and Oggiano, L..
Low Aerodynamic Drag Suit for Cycling - Design and Testing.
In Proceedings of the 3rd International Congress on Sport Sciences Research and Technology Support (icSPORTS 2015), pages 89-96
ISBN: 978-989-758-159-5
Copyright
c
2015 by SCITEPRESS Science and Technology Publications, Lda. All rights reserved
89
design that could improve the overall aerodynamic
performance of the pro cycling suit produced by
Trimtex Sport AS using facilities in the wind tunnel
laboratory at the Department of Energy and Process
engineering at the Norwegian University of Science
and Technology (NTNU). In the preliminary tests,
cylinders are covered with 27 different fabrics and
tested in a wind tunnel to separately assess the flow
around each body part. This method has been used
in several previous studies with good results (Bardal
and Reid, 2012: Chowdhury et al., 2010, Underwood
and Jermy, 2011; Oggiano et al., 2013). The most
promising fabrics were also tested on tandem
cylinders and with a steel grid creating intense
turbulent flow in the tunnel. Two different cycling
kits with the original design but patched with the
new materials and one jersey with an alternative
design have been tested on both cyclists and full-size
upper and lower body mannequins.
1.1 Rules and Regulations
According to the UCI (Union Cycliste
Internationale) regulations for clothing material,
only “plain textile material” with no other purpose
than that of clothing can be used. Textile is here
defined as “a material made up of yarns and fibres
which has an open mesh “fabric” structure”. No
seams should be present on a suit that does not hold
two pieces of fabric together and coating other than
logos and labels are not allowed .The apparel should
serve the unique purpose of clothing and has to
“conform to the curve of the body in any case”
without any “non-essential parts” to improve
aerodynamic resistance (UCI, 2012). All materials
tested in this project comply with the UCI
regulations.
2 METHODS
2.1 Fabric Testing
2.1.1 Experimental Setup
The measurements were conducted in a small scale
wind tunnel at NTNU with a cross section of
0,55x1,0 meters and a maximum wind speed of 28
m/s. To measure the wind speed, a pitot tube was
placed 2,70 m in front of the cylinder. The
temperature was monitored by a thermocouple type
K (chromel-alumel) and its value used to calculate
density and dynamic viscosity of the airflow. The
forces on the cylinder were measured by an AMTI
BP400600HF force plate that consists of strain
gauges in three directions. In this experiment, only
the drag- or y-direction force was used.
When riding aggressively, the shoulder and
upper arm are positioned perpendicular to the flow.
Riding slightly more upright, the angle increases to
10 or 15 degrees. The critical Reynolds number
remains constant with various angles of attack while
a rough surface reduces cylinder drag for angles up
to 25 degrees (Oggiano et al., 2013; Chowdhury,
2012). Testing was therefore conducted on cylinders
positioned with the long axis perpendicular to the
flow. The fabrics for the torso was also tested on a
vertical cylinder as the differences in friction drag
can be foreseen from a vertical cylinder
measurement (Bardal and Reid, 2012).
Two circular cylinders with diameters of 11 and
16 cm were used. The smallest cylinder was 40 cm
long with a gap of 9,7 cm above and 5,0 cm below
while the largest cylinder was 47 cm long with 4,3
cm above and 3,4 cm below. The smooth fabrics for
the torso were tested on the 16 cm diameter cylinder
because of the lower velocity drag crisis on this
cylinder, while the rougher fabrics were tested on
the 11 cm diameter cylinder.
The steel grid used to create turbulence had
circular bars 10 mm in diameter and cells of size
40x40 mm that covered the whole cross section of
the tunnel. It was placed 0,35 m behind the pitot
tube and 2,35 m in front of the cylinder. The flow
produced by the grid was probably of too high
turbulence intensity compared with normal outdoor
conditions although it was not measured.
Nevertheless, the results indicate how disturbances
in the flow affect the drag of various surface
structures.
For the measurements with tandem cylinders, the
11 cm diameter cylinder was placed with a
separation distance of 17 and 23 cm in front of the
larger cylinder of 16 cm diameter. Drag was
measured on the second cylinder only. This
configuration is a simplification of one limb in front
of another such as an arm in front of a thigh.
2.1.2 Textiles
The fabrics were fitted with 25% stretch. According
to Oggiano (Oggiano et al., 2013), there is a weak
linear relation between the critical velocity and the
stretching of the fabric, but he concludes none the
less that it does not seem to affect the flow
transition. Bardal found that stretch is of no practical
significance in the design of alpine skiing suits
(Bardal and Reid, 2012). The textiles tested in this
icSPORTS 2015 - International Congress on Sport Sciences Research and Technology Support
90
project are significantly thinner than textiles used in
an alpine suit, so it may all the same be a minor
factor. All textiles were tested with the seam centred
on the leeward side to minimize its influence.
Sublimation printing was done prior to testing since
the print makes the surface smoother and thereby
changes the aerodynamic properties (Oggiano et al.,
2013).
Figure 1: Upper and lower body mannequins.
2.2 Full Scale Testing
2.2.1 Experimental Setup
Testing of the cycling kits on the mannequin models
and cyclist were conducted in the large wind tunnel
at NTNU. It is equipped with a 220KW fan engine,
has a maximum speed of 30 m/s and the test section
measures 2,7x1,8x12,5 meters. A pitot tube and a
thermocouple type K was used to monitor the wind
speed and temperature respectively. The drag was
measured with a Schenck six component force
balance where only the axis of the drag direction
was used. The drag forces presented are normalized
to 20 degrees celsius.
2.2.2 Mannequin Models
Testing on both mannequin models was conducted at
five velocities ranging from 35 to 72,5 km/h or 9,7
to 20,1 m/s. The mannequin used for testing the
jersey was a full-scale upper body including head
and upper arms belonging to a model of height 170
cm and weight 70 kg. Its position was adjusted to
imitate that of a cyclist in the drop bars and the
forearms removed to reduce the amount of
uncertainty. The lower body mannequin had an inner
leg length of 90 cm with a mid-thigh circumference
of 58 cm. Only one leg was used with the other cut
at 16 cm. A 1,0 cm thick plate fixed the loose part of
the shorts. Photographs of the mannequins are
presented in Figure 1.
Figure 2: Cyclist in an upright dropped position.
In addition to drag measurements of the jerseys,
measurements were conducted on all combinations
of jerseys and sleeves to investigate the
contributions from sleeves separately. To examine
the importance of sleeve length, drag measurements
were conducted with the mannequin wearing
nothing but the different sleeves in both the original
length (17 cm) and elbow length (30.5 cm). Note
that when the original length is used on the loose
sleeves, they do not have the smooth 4 cm bi-elastic
band at the ends. The loose sleeves therefore have
the sleeve material 4 cm longer than the jersey
sleeves.
2.2.3 Cyclist
A regular road bike was placed on a roller so that the
tires were not touching the wind tunnel floor. The
front wheel was kept stationary and supported by a
custom-made wheel stand. The back wheel was only
spinning in the dynamic tests. The cyclist was
positioned comfortably in the drop bars and live
video acquired from a side-mounted camera was
projected on the floor in front of the rider. The video
was showing the position superimposed with an
outline of the initial position in order to keep it as
consistent as possible.
Mean values of the drag force were calculated
from three times 30 seconds dynamic pedalling on a
cadence of 90 RPM and three times 30 seconds
static with left leg at 0 degrees (Figure 2). This was
done alternately a total of three times at each of the
velocities, 35, 50 and 65 km/h (9,7, 13,9 and 18,1
m/s).
Low Aerodynamic Drag Suit for Cycling - Design and Testing
91
Table 1: Mean velocity distribution from an assortment of
men’s elite road races.
26-35kmh
(7-10ms)
36-45kmh
(10-13ms)
46+kmh
(13+ms)
National 0.267 0.378 0.356
International 0.241 0.408 0.351
Total average 0.254 0.393 0.354
2.3 Speed and Force Calculations
Based on a total of eleven men’s elite road races, the
mean velocity distribution for three domains was
found. Not counting velocities less than 25 km/h, the
percentage of total time in each domain is listed in
Table 1. The velocity profile was used to calculate
the weighted mean drag of the materials.
Assuming similar conditions for an individual
time trial (ITT) as in a solo breakaway or in front of
the peloton, ITT races are used to illustrate time
savings of the various apparel. Theoretical time
savings were calculated using Bassett's empirical
model (Bassett, 1999) from his study of hour records
from 1967 to 1996. The dropped position on the
road is identical to that of Eddy Merckx in 1972, but
modern bicycles and cycling suits have lower drag
than those used in Bassett's study. The power P
needed to overcome air and rolling resistance on a
cycling track is:
P
= 0.00953
M
V + 0.00775V
2
+ 0.007551
A
V
3
(2)
M is the total weight of the cyclist and the bike in
kilos, A is the frontal area and V is the velocity.
The time savings are illustrated on two
constructed persons. Person 1 has a weight of 70kg,
person 2 60 kg and the bikes 7 kg. With respective
heights of 1.83 and 1.70m correspondingly, the
frontal areas of person 1 and 2 are 0.337 and
0.308m
2
using Bassett’s formula for frontal area
(Bassett, 1999).
3 RESULTS
3.1 Jersey
3.1.1 Fabric Testing
The results from the cylinder tests of the original and
chosen jersey materials are shown in figure 3 plotted
against the velocity normalized to common racing
conditions of 20 degrees and 1 atm. Table 2 shows
the material used on the various jersey patches.
Figure 3: Jersey material on 11 and 16 cm cylinders. The
C
D
values are normalised with the sub-critical C
D
.
Table 2: Material used in the different fabric zones.
Jersey A Jersey B Jersey C
Front #2 #3 #3
Back #1 #3 #3
Upper Back #2 #5 #3
Sides #1 #5 #4
Sleeves #3 #5 #6
Whereas the original jersey (A) has relatively
smooth materials on all panels, the differences in
surface roughness on the new jerseys are more
pronounced. Since the flow pattern around a cyclist
throughout a stroke is asymmetrical with an “S”
forming on his back (Crouch et al., 2012), the fabric
on the back should be homogenous and as smooth as
possible such as fabric #3. This thin and breathable
fabric is used on the front and back on jerseys B and
C. Fabric #5 has an asymmetrical mesh-like
macrostructure similar to prism formed dimples with
microstructure in the dimples and no fuzziness while
fabric #6 has a traditionally dimpled structure with a
smooth surface. With a minimum drag coefficient of
0.47 at Reynolds number 107 000, fabric #5 seems
equally or better suited to enhance transition on the
prioritized velocities than most textiles tested by
others (Chowdhury et al., 2010; Brownlie et al.,
2009; Bardal and Reid, 2012). The weighted mean
of the drag coefficients of fabric #5 was 0.686 while
the mean for #6 was as low as 0.652 due to its lower
post-critical drag. The latter could be owing to its
smooth and dimpled surface structure since this can
reduce post-critical drag with respect to other kinds
of structure (Zdravkovich, 1990; Bearman and
Harvey, 1993; Oggiano et al., 2013). Fabric #5 is
used on the sleeves, sides and top of the back of
jersey B aiming to enhance transition to turbulence
icSPORTS 2015 - International Congress on Sport Sciences Research and Technology Support
92
in the boundary layer at the patches most exposed to
the free stream. Jersey C is a compromise between
jersey A and B with fabric #6 on the sleeves and the
sheer and semi-smooth fabric #4 on the sides.
The resulting drag profiles using the steel grid
show, as expected, that a less rough surface structure
is needed to enhance transition at the same velocities
when the flow is turbulent. The fact that smoother
materials were more influenced by the turbulence
emphasizes the importance of a smooth surface
where friction drag is dominant such as on the back
of a cyclist. These effects are also observed for the
tested bib fabrics. The intense turbulence amplified
the post-critical differences in drag for fabric #5 and
#6 from 3,5 to 5%, possibly indicating an
accentuated effect of dimpled surfaces in turbulent
flow. The smoother surface of fabric #6 is most
likely an important factor as well although it did not
alter the critical velocity with respect to fabric #5.
3.1.2
Full Scale Testing
The jerseys were tested on the mannequin against
the original Trimtex Pro cycling jersey. Whereas the
drag coefficients of jersey B and C are constant and
nearly identical, the original jersey A clearly has a
higher drag at low speeds as seen in figure 4. The
difference decreases with increasing velocity and
stabilizes at 15 m/s. The improvement in drag force
is 25-35 grams at all velocities with a standard
deviation of 8 grams or 0.37%. Table 3 shows how
the performance is improved by the reduced drag.
The fact that the drag on jersey B and C were nearly
identical can indicate that the sleeves are the largest
contributor, and that the rougher panels on jersey B
do not have a significant impact on the flow.
Figure 4: Jerseys tested on mannequin with error bars.
To study how the drag is affected by sleeve
roughness alone, loose sleeves of the respective
qualities where placed on top of the original jersey.
Figure 5 shows that the drag is nearly equal for all
sleeves up to 14 m/s where the rougher sleeves have
similar and increasingly lower drag at higher
velocities. At 19 m/s the difference is 26 grams for
#5 and 43 grams for #6 compared with sleeve #3.
Lengthening the loose sleeves to the elbows, the
overall drag is lowered with the ratios kept constant
so that the difference between the sleeves doubles to
54 grams for #5 and 87 grams for #6. These
differences are expected based on the cylinder
measurements and are assumed to be a result of the
dimpled surface structure of fabric #6. Note that the
drag obtained with loose sleeves cannot be
compared directly to the drag of the full jerseys
since the loose sleeves are tucking in some extra
fabric in the armpits.
Figure 5: Effects of sleeve length and roughness from the
mannequin tests with error bars showing the standard
deviation.
Both figure 4 and 5 indicate a critical velocity at
13-15 m/s on jersey A that corresponds to Reynolds
number 85 000 for the arms of the mannequin. The
arm had a circumference of 28 cm, so these results
are in good correspondence with the critical velocity
of fabric #5 and #6 at Reynolds number 85 000 on
the 11 cm cylinder. The transitions seem to have
taken place at even lower velocities for jersey B and
C due to the rougher patches. However, the effect of
a rough sleeve fabric will in all probability be less
on a cyclist than on the mannequin due to increased
disturbance in the flow.
A fourth jersey (D) was designed based on the
mannequin tests. Its materials are similar to those of
jersey C but the sleeves are extended by 2 cm and
the elastic grip has a slightly structured surface. The
elastics on both sleeves and pockets are tightened to
minimise flapping. The side panel is wing shaped so
that the seam runs in the stream-wise direction to the
back extending the front patch along the lower sides
of the jersey.
Figure 6 shows the drag difference of jersey B, C
and D with respect to the original jersey (A) when
Low Aerodynamic Drag Suit for Cycling - Design and Testing
93
tested on the cyclist. All jerseys have similar
properties at 9,7 m/s, but the rougher jerseys have a
clear advantage at higher velocities. Surprisingly,
jersey D had higher drag than the other jerseys
despite the assumed profitable changes in design. By
tightening the pocket band, wrinkling perpendicular
to the flow increased somewhat on the sides of the
torso. This could be the main reason for the increase
in drag compared with jersey C since the material in
the side panels do not seem to play a critical role. As
listed in table 3, the improvement of jersey C with
respect to the original jersey is of 60 grams or 8.2
watts at 13,9 m/s (50 km/h).
Figure 6: Dynamic testing on cyclist. Difference in drag
(grams) of jersey B, C and D compared with jersey A,
with error bars.
The dynamic tests show approximately 5% lower
drag than the static tests, and the differences
between the jerseys were smaller, probably due to
the fact that leg motion will trigger flow transition
(Brownlie et al., 2009). The standard deviations
were 15 grams or 0.33% for the dynamic tests and
19 grams or 0.43% for the static tests.
Figure 7: Bib fabric with and without grid on a 16 cm
diameter cylinder. The C
D
-values are normalised with
sub-critical C
D
.
Wearing a correctly fitted jersey is of outmost
importance. The jersey in size small fitted the cyclist
comfortably yet tightly with few wrinkles and would
be the natural choice for a racing jersey. The
medium-sized jersey was still relatively tight and
well fitted, but the wrinkles on the side panels were
more pronounced. This seemingly small difference
in size increased the
drag by 104 grams or 14 watts
at 50 km/h, as shown in the last line of Table 3.
3.2 Bib Shorts
3.2.1 Fabric Testing
The flow around the thighs is the most difficult to
Table 3: Theoretical drag, power and time savings of the various jerseys and bibs at 50km/h compared with the original kit.
Mannequin
Drag
difference (g)
Power
difference (W)
Drag increase* (%) Time difference 1h, 50km/h (s)
Person 1 Person 2 Person 1 Person 2
Jersey B -30 -4.1 -1.1 -1.2 -00:14 -00:16
C -33 -4.5 -1.2 -1.3 -00:15 -00:17
Bib B -9 -1.2 -0.3 -0.4 -00:04 -00:05
C -22 -3.0 -0.8 -0.9 -00:10 -00:11
Cyclist
Jersey B -32 -4.4 -1.2 -1.3 -00:15 -00:17
C -60 -8.2 -2.2 -2.4 -00:28 -00:31
D 0 0 0 0 00:00 00:00
Bib B -4 -0.5 -0.2 -0.2 -00:02 -00:02
C -35 -4.8 -1.2 -1.4 -00:16 -00:18
Sizing
Jersey size M +104 +14.2 -3.8 -4.2 +0:48 +00:53
*From 374W for person 1 and 340W for person 2
icSPORTS 2015 - International Congress on Sport Sciences Research and Technology Support
94
predict as the free stream flow is disturbed upstream
by the front wheel, cockpit and forearms in addition
to the thigh movements. As the flow regime
characterizing the aerodynamics of a cyclist changes
throughout the stroke cycle, materials with an
asymmetrical pattern having varying properties
depending on the leg position could present an
interesting compromise. When in the upper part of
the stroke, the air remains attached alongside the
thigh and follows a downward trajectory into the
wake. With the leg perpendicular to the flow, the
flow separates over the hip following an upward
path into the wake (Crouch et al., 2012). A striped
pattern aligned with the thigh would therefore be
alternately in line with the flow having the
properties of a smooth fabric and perpendicular to
the flow enhancing transition. Various striped
patterns were tested against traditional smooth
materials and fabrics with a homogenous structure.
On the 16 cm cylinder, a broadly striped material
with a smooth surface (#21) had the lowest critical
velocity while the original smooth fabric #23 did not
undergo transition even at 25 m/s. A narrowly
striped fabric (#22) with properties in between of the
two extremes was chosen alongside fabric #21 for
further testing against the original bib. The results
are shown in Figure 7 both with and without grid in
the tunnel and favour the broadly striped fabric.
With the cylinders in tandem configuration, a rough
surface texture is desired at the rear cylinder
regardless of the distance to and surface roughness
of the cylinder in front. Nevertheless, the importance
of the material on the second cylinder decreased
significantly with decreasing distance between the
two cylinders. The effect is similar to that of the grid
produced turbulence confirming that disturbances in
the flow reduce the effect of surface roughness.
3.2.2 Full Scale Testing
Bib A is the original bib with fabric #23 while fabric
#21 and #22 is used on bib B and C respectively.
Testing on the one-legged lower body mannequin
was conducted to study the effect of three-
dimensional effects due to the shape of the thigh
muscles. A clear drop in the drag coefficient is seen
in Figure 8 for all bibs at 15 m/s, but eventual
variations in critical velocity are not pronounced.
The original smooth bib had highest sub-critical drag
while bib C had the lowest. The super-critical values
were similar for all bibs. A fourth bib with a slightly
rougher bi-elastic band was also tested, but the
influence was too small to be observed. The standard
deviations were 10 grams or 0,53%.
Figure 8: Bib shorts tested on mannequin with error bars.
When tested on the cyclist, the difference
between bib A and B was less than the standard
error on both the dynamic and static tests while bib
C had the lowest drag in both cases with 35 grams or
5 watts less drag than bib A at 50 km/h. The results
presented in Figure 9 indicate that bib B enhanced
transition at velocities slightly lower than bib A and
that the rough surface of bib C led to the highest
super-critical drag. These changes in properties
compared with the cylinder measurements may be
explained by increased stretching of the fabrics on
the mannequin and the cyclist. The surface structure
of bib B became less pronounced than on the
cylinder and bib C got a rougher, more homogenous
surface.
Figure 9: Dynamic testing on cyclist. Difference in drag
(grams) of bib B and C compared with bib A, with error
bars.
4 CONCLUSION
The cycling kit developed in this project has
considerably lower drag than a traditional kit with
smooth fabrics only. Rough material on the sleeves
clearly improves the aerodynamic qualities of a
jersey, and the results indicate that dimpled fabric
having a smooth surface is favourable to other types
of surface morphology. Since the gain increases with
Low Aerodynamic Drag Suit for Cycling - Design and Testing
95
sleeve length, the sleeves should be as long as
comfort and regulations allow. A structured surface
is preferred on bib shorts as well. The rough
materials tested in this project were the roughest
currently available fabrics both complying with the
UCI regulations and suitable for use in a cycling kit.
It is likely that a sleeve and bib material with a more
pronounced surface structure could further reduce
the drag. Jersey designs with the seams to a greater
extent in the stream-wise direction and distinctly
striped bib material are of particular interest for
future work.
The results from this project can be applied to
other cycling garments. Loose sleeves normally have
a smooth fabric all over but should rather have a
rough surface on the part covering the upper arms.
The same applies to time trial suits. Loose legs
should probably be of the same material as the bib
shorts above the knee, and transition could be
induced on the lower leg by a rougher material
(Brownlie et al., 2009) as in speed skating (Sætran
and Oggiano, 2008). Aerodynamic shoe covers
should likewise be roughly structured above the calf.
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