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ORIGINAL ARTICLE

An experimental study on aerodynamic performance of time trialbicycle helmets

Harun Chowdhury • Firoz Alam

� International Sports Engineering Association 2014

Abstract Aerodynamic efficiency is one of the important

criteria for racing bicycle helmets, especially in time trial

event. The physical characteristics of a bicycle helmet

especially its venting geometry, position and number of

vents play a crucial role in the aerodynamic efficiency of

the helmet. Despite the importance of this, little informa-

tion on aerodynamic behaviour of racing bicycle helmets is

available. In this study, a series of commercially available

time trial helmets were investigated in a wind tunnel

environment over a range of wind speeds, and yaw and

pitch angles to understand their aerodynamic behaviour. In

order to obtain as realistic a data as possible, an instru-

mented mannequin was used in the wind tunnel testing.

The experimental findings indicate that the aerodynamic

performance of current production time trial helmets varies

significantly. The results also show that helmet length as

well as vent geometry and vent area have significant effects

on aerodynamic drag of a time trial helmet. A time trial

helmet having longer length and smooth vents with mini-

mum vent area can reduce aerodynamic drag significantly.

Keywords Time trial helmet � Aerodynamic drag � Drags

area � Bicycle � Wind tunnel

1 Introduction

In elite bicycle competitions, especially in time trial event,

alone with cyclist body position, cycling equipment, such

as helmet, has influences on the overall aerodynamic per-

formance of a cyclist. Thus, an aerodynamically efficient

helmet can make the difference between a winner and a

loser as the wining time margin is significantly small. In

time trial cycling, at speeds over 50 km/h, 50–80 % of total

resistance is aerodynamic drag [1–3]. Out of the total

aerodynamic resistance, the cyclist body position along

with helmet and clothing generates approximately 70 % of

this and the remaining aerodynamic drag is produced by

the bicycle and other accessories [4, 5]. The helmet alone

can generate around 2–8 % of the total aerodynamic drag

at speeds of 30 km/h and over [6, 7]. Therefore, an aero-

dynamically efficient helmet can provide a competitive

advantage and by selecting appropriate helmets and

maintaining correct body position, a cyclist can reduce

aerodynamic drag notably and the conserved energy can be

used at appropriate stages of racing.

Most of the commercially produced time trial helmets

do not comply with the minimum safety standards for head

protection as their main function is to minimise aerody-

namic drag only. However, very few helmets comply with

the safety standards. The aerodynamic performances of

widely used commercially available helmets are not widely

reported, and often helmet manufacturers claim and

counterclaim about their helmet’s relative aerodynamic

advantages without providing any scientific proof. The

Australian safety standard for bicycle helmet is one of the

toughest in the world. Cyclists must comply with the

Australian Road Rules which states that in all Australian

cycling events, on the road and track, a helmet complying

with the Australian Standard (AS2063) must be worn.

However, an UCI (Union Cycliste Internationale) approved

(e.g., ANSI, SNELL or EN) aero helmet can be used for

individual pursuits and individual time trial cycling. In

team pursuits, only an AS/NZS 2063 regulation helmet can

H. Chowdhury (&) � F. Alam

School of Aerospace, Mechanical and Manufacturing

Engineering, RMIT University, Plenty Road, Bundoora,

Melbourne, VIC 3083, Australia

e-mail: [email protected]

Sports Eng

DOI 10.1007/s12283-014-0151-5

be used, whereas in road racing events, an UCI approved

helmet can be used. Participants looking for any small

advantage in the competition at elite level in Australia,

therefore, require a time trial helmet that must comply fully

with the Australian Standards. At present, only two man-

ufacturers’ time trial helmets comply with the Australian

Standard (AS2063) according to Australian Cycling

Organisation website [9].

Several studies [4–8] have been undertaken to measure

the aerodynamic drag for recreational bicycle helmets;

however, little study has been conducted primarily to

understand the aerodynamic behaviour of production time

trial helmets except for Alam et al. [5] and Blair and

Sidelko [8]. Furthermore, little information is available on

comparative study of the aerodynamic performance of time

trial helmets. Therefore, the primary objectives of this

study are to investigate the aerodynamic performance of

four commercially available top ranking and widely used

time trial helmets and to establish a correlation with their

various design features, for instance, the number of vents,

vent geometry and their location on the helmet.

2 Experimental procedure

2.1 Description of helmets

In this study, four commercially available time trial hel-

mets (see Fig. 1) manufactured by Limar, Louis Garneau

(LG) and Giro were selected. The reason for selecting these

helmets was mainly because of their widespread use in

competitive racings around the world and also their easy

availability in Australia. Out of these four time trial hel-

mets, two are: Limar Crono 05 and Limar Speed Demon.

The other two helmets are: Giro Advantage and LG

Rocket. The Crono 05 is 330 mm long with a mass of

330 g and it is made of expanded polystyrene foam using

in-mould construction techniques. The Limar Speed

Demon features an expanded length design targeting road

time trial cyclists and tri-athletes (i.e., longer race dis-

tances). The Speed Demon is 385 mm long, weighs 340 g

and is constructed from expanded polystyrene foam using

in-mould construction techniques. The Speed Demon has

15 air vents, of which 12 are forward facing. On the other

Fig. 1 Time trial helmets:

a Limar Crono 05; b Limar

Speed Demon; c LG Rocket;

d Giro advantage

H. Chowdhury, F. Alam

hand, Crono 05 has only 5 vents. Additionally, it does not

have any forward facing ventilation holes. The Giro

Advantage is around 380 mm long and LG Rocket is

around 405 mm long. The LG Rocket is heavier than the

Giro Advantage (e.g., LG Rocket’s mass is 507 g and the

Giro Advantage’s mass is around 366 g including the

straps). Both helmets are made of micro-shell with ergo-

nomic padding. However, LG Rocket differs from Giro

Advantage for vent numbers. The LG Rocket has only 4

vents at the front and 3 vents at the rear (7 in total). In

contrast, the Giro Advantage has 5 vents at the front and

there is no vent at the rear. The vents in Giro Advantage are

relatively larger compared to those in LG Rocket. ImajeJ

software was used to quantify the frontal area of the helmet

and the frontal vents for each helmet as shown in Fig. 2.

Percentage of frontal vent area to the total frontal area of

the helmet was calculated [3]. The details of vents for all

four helmets are given in Table 1.

2.2 Experimental facilities

In order to measure the aerodynamic drag experimentally,

the RMIT Industrial Wind Tunnel was used. The tunnel is a

closed return circuit wind tunnel with a maximum speed of

approximately 150 km/h. The dimensions of the rectangular

test section are 3 m (wide), 2 m (high) and 9 m (long). The

tunnel is equipped with a turntable to yaw a suitable sized

model. More details about the tunnel physical properties

including turbulence intensity and physical dimensions can

be found in [10]. A purpose-made mannequin was designed

and manufactured to simulate the body position and size of

a representative road cyclist (see Fig. 3). Body measure-

ments were taken of several male cyclists and the averaged

dimensions were used to shape the model. The head of the

mannequin was connected to a rotating mechanism in order

to change the pitch angle (h). The mannequin was mounted

on a rectangular platform which was connected through a

threaded stud to a six-component force sensor (manufac-

tured by JR3 Inc, USA). The sensor was capable of

Fig. 2 Frontal projected areas

of the vent and helmets

Table 1 The details of vents for all helmets tested

Helmet

name

Length

(mm)

Mass

(kg)

Vent shape Number

of front

vents

Vent

area

(%)

Lemar

Crono 05

330 0.330 Triangular

and mixed

(smooth)

0 0

Lemar

Speed

Demon

385 0.340 Ellipsoidal

(smooth)

12 11

LG Rocket 405 0.507 Rectangular

(sharp)

4 5

Giro

Advantage

380 0.366 Ellipsoidal

(smooth)

5 8

Fig. 3 Experimental setup in RMIT Industrial Wind Tunnel

Fig. 4 Mannequin head: a without helmet (bareheaded); b with a

helmet fitted

An experimental study on aerodynamic performance

measuring all three forces (drag, side and lift forces) and

three moments (yaw, pitch and roll moments) simulta-

neously. Initially, the force measurements were taken on the

bareheaded mannequin for baseline comparison. Then the

drag forces were measured for each helmet by fitting the

helmet onto the mannequin head (see Fig. 4). Drag areas

(CDA) were calculated by using Eq. (1).

CDA ¼ D12q V2

m2� �

ð1Þ

where, D, q and V are the drag force (N), air density (kg/

m3) and wind velocity (m/s), respectively. Drag area is a

product of drag coefficient (CD) and the projected frontal

area (A) of an object and it also indicates the actual drag

acting on the object.

The aerodynamic drag force over a range of wind speeds

(30–70 km/h) at three pitch angles (h = 30�, 45� and 90�)

were measured. Additionally, the effects of yaw angle (w)

at 0�, 30� and 45� were also measured to simulate the

crosswind effects on aerodynamic drag. It may be worth

mentioning that the head position at w = 0� and h = 45�are more realistic as this position is most practical and

widely used in competitive time trial bicycle racing [4–8].

3 Results

The drag area (CDA) as a function of speeds at w = 0� and

h = 45� for all four helmets and the bareheaded manne-

quin (baseline) are shown in Fig. 5. The Giro Advantage

helmet displays the lowest CDA value compared to all other

helmets. The Giro Advantage has shown the CDA value of

21, 42 and 55 % lower compared to LG Rocket, Crono 05

and Speed Demon, respectively. The drag areas for all

helmets decrease with an increase of speeds which is likely

to be due to the elimination of local flow separations at

high speeds. The Speed Demon and Crono 05 display

higher drag values from the baseline, whereas LG Rocket

and Giro Advantage has lower drag for all speeds tested

(see Fig. 5).

The CDA values from this study agree well with previ-

ously published data by Alam et al. [5] for the bareheaded

mannequin where it was shown that the CDA value was

close to 1.49 at 70 km/h speed. At low speeds, the flow

Advantage

Rocket

BaselineCrono 05

Speed Demon

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

35 45 55 65 75

Dra

g A

rea

(CD

A)

Speed (km/h)

Fig. 5 The variation of drag area with speeds at w = 0� and h = 45�

Advantage

Rocket

Baseline

Crono 05

Speed Demon

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

35 45 55 65 75 85 95

Dra

g A

rea

(CDA

)

Pitch angle

Fig. 6 The variation of drag area with pitch angles (h) at w = 0� and

V = 50 km/h

Advantage

Rocket

Baseline

Crono 05Speed Demon

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1.90

2.00

0 10 20 30 40 50

Dra

g A

rea

(CD

A)

Yaw angle

Fig. 7 The variation of drag area with yaw angles (w) at h = 45� and

V = 50 km/h


around the bareheaded mannequin is not streamlined as it is

generally at high speeds. Therefore, the CDA value for the

bareheaded mannequin is approximately 1.47 at 50 km/h

and 1.49 at 70 km/h.

The variation of drag area with pitch angles at 0� yaw

angle for 50 km/h wind speed is shown in Fig. 6. The drag

areas of Speed Demon and Crono 05 decrease with an

increase of pitch angle. With the increase of pitch angles,

the gap between the head and the back of the mannequin

torso becomes streamlined which may eliminate the local

flow separation immediately behind the helmet. A similar

trend for other speeds was also noted. However, the drag

areas of LG Rocket and Giro Advantage increase with an

increase of pitch angles. These changes in aerodynamic

behaviour are due to the helmet design features, such as

vent geometry, position, length and external shapes.

The effects of yaw angles on drag areas at 45� pitch

angle for 50 km/h speed are shown in Fig. 7. It can be

clearly seen that with an increase of yaw angle, the drag

area also increases for the bareheaded mannequin, Crono

05 and Speed Demon. However, a reduction in drag area

was noted for the LG Rocket and Giro Advantage helmets

at high yaw angles. It is believed that some structural

deformation at the tip of these two helmets might have

occurred at high yaw angles as the tip was not reinforced

with the interior foam.

4 Discussion

The average drag reduction or increase (in percentage)

from the baseline over a range of speeds (40–70 km/h) is

shown in Fig. 8. At all speeds, the Giro Advantage has

significant reduction of drag (approximately 17 %)

compared to the baseline, whereas the LG Rocket has a

negligible advantage. However, both Speed Demon and

Crono 05 show a significant increase of drag over the

baseline (17 % for Limar Crono 05 and 27 % for Limar

Speed Demon).

The external physical shapes of Giro Advantage and LG

Rocket are similar, whereas the physical shapes of Crono

05 and Speed Demon are different from other two helmets.

Nevertheless, Crono 05 and Speed Demon have similar

external shapes except the length. The Giro Advantage has

five vents compared to seven vents of LG Rocket. All five

vents of Giro are located at the front of the helmet. Crono

05 has no frontal vent and its length is the shortest among

all other helmets tested. The result indicated an increase of

average drag by 17 % compared to the baseline. Although

Speed Demon is longer than Crono 05 and Giro Advantage,

it has 27 % more drag compared to the baseline. It can be

clearly seen that Speed Demon has more number of vents

as well as greater vent area (11 %) than that of other hel-

mets. On the other hand, LG Rocket, the longest among all

four time trial helmets tested, having lesser vent area (5 %)

indicated a maximum of 2 % reduction of drag from the

baseline. Results also indicated a significant reduction of

drag (around 17 %) from the baseline for Giro Advantage.

Despite having more vent area than LG Rocket, the shape

of the vent is smoother compared to the sharp rectangular

vents of LG Rocket. Additionally, the length of the LG

Rocket is longer than Crono 05.

Therefore, it can be clearly seen that helmet length as




mum area can reduce aerodynamic drag. Generally, vents

are necessary to provide thermal comfort. Therefore, the

vent needs to be designed based on aerodynamic advantage

along with heat dissipation characteristics. Smooth-vented

long-length time trial helmet can increase aerodynamic

efficiency without affecting the thermal comfort.

5 Conclusions

The experimental findings indicate that the aerodynamic

performance of current production time trial helmets varies

significantly. Giro Advantage was by far the most aero-

dynamically efficient helmet. On the other hand, Limar

Speed Demon was the least performing helmet compared

to all other helmets in time trial category tested. The effects

of crosswinds on aerodynamic drag were considerable.

Generally, the aerodynamic drag increases with yaw

angles. Additionally, it was noted that helmet length as



Giro Advantage

LG Rocket

Crono 05

Speed Demon

-30%

-20%

-10%

0%

10%

20%

30%

40%Pe

rcen

t var

iatio

n in

dra

g ar

ea f

rom

the

base

line 40 km/h

50 km/h

60 km/h

70 km/h

Fig. 8 Percent difference in drag area from the baseline at w = 0�,

h = 45� and V = 50 km/h

An experimental study on aerodynamic performance


mum vent area can reduce aerodynamic drag significantly.

Smooth-vented long-length time trial helmet can increase

aerodynamic efficiency with keeping the thermal comfort

intact.

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