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Minguez, J. M. and Vogwell, J. (2008) An analytical model to
study the radial stiffness and spoke load distribution in a
modern racing bicycle wheel. Proceedings of the Institution of
Mechanical Engineers, Part C: Journal of Mechanical
Engineering Science, 222 (4). pp. 563-576. ISSN 0954-4062
Link to official URL (if available):
http://dx.doi.org/10.1243/09544062jmes802
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RADIAL STIFFNESS
OF A
BICYCLE WHEEL
-
AN ANALYTICAL STUDY
José María Mínguez (corresponding author)
Dpto. de Física Aplicada II
Facultad de Ciencia y Tecnología
Universidad del País Vasco
Aptdo. 644
48080 Bilbao
SPAIN
Email: josemaria.minguez@ehu.es
Jeffrey Vogwell
Department of Mechanical Engineering
Faculty of Engineering and Design
University of Bath
U. K.
2
Abstract
A theoretical analysis is carried out to study the behaviour of the structural
components of a spoked bicycle wheel when radially loaded. This has been done so
as to establish convenient mathematical relationships for quantifying the individual
contributions which the spokes and the rim make to the radial stiffness of the wheel.
The effect of spoke pretension is considered and also the influence that this has on
the efficient distribution of load and upon the strength of the wheel components.
Keywords: radial stiffness, bicycle wheel, spokes, rim, pretension
Introduction
Although the wheel has been around for millennia and the bicycle wheel for
over a century, there are still radical changes being made to the design of the
modern spoked bicycle wheel (Chandler, 2002). Racing cycle wheels, as used in the
Tour de France for example, have changed substantially from the multi-spoke
wheels with open cross section wheel rims as used on the traditional racing bike
(Schraner, 1999; Okajima et al. 2000; Muraoka et al. 2001). Leading bicycle wheel
manufacturers, such as Mavic and Shimano, have developed wheels which
efficiently use few metal spokes that attach to wheel rims which comprise part
closed and open cross sections. Modern materials, such as carbon fibre, and
developments in forming techniques have resulted in wheels manufactured as single
items, effectively having even fewer spokes, and such wheels are widely used in
speed racing on velodrome circuits
The requirements of a modern bicycle wheel are many. The wheel must
transfer the weight of the cyclist (via the frame, forks and axle) radially from the
wheel hub to the rim and thus to the ground (via the tyre). In order to achieve
traction, and thus wheel rotation, torsion must be transmitted from the chain
sprocket (attached to the hub) to overcome rolling resistance at the tyre (which fits
within the rim). In addition, a wheel must be sufficient strong to withstand shock
loads when riding over bumpy terrain and withstand cornering loads (Gordon,
3
2004). Also the rim must run true and the spokes play a major role in achieving this
together with the selection of appropriate materials (McMahon and Graham, 1992).
Understanding how a spoked wheel works is clearly essential but perhaps
not immediately obvious as pre-tensioning of the spokes is fundamental to a wheel
functioning efficiently, as shown by Dietrich (1993, 1999). Without pre-tightening
of the spokes, for example, the weight would only be supported by those spokes in
tension as the spokes in the lower half of the wheel would be in compression and,
because of the slender shape of a spoke, it means that they will buckle rather than
support any appreciable compressive load.
Traditionally wheels have used many spokes and this is because the open
section rim lacked rigidity and would distort too much if the spacing between
successive spokes were large (Brandt, 1993). However, modern rims are much
more rigid in bending and torsion because of the part closed cross-section and so
fewer spokes can be used, according to Hed and Haug (1989) and Muraoka et al.
(2001). An optimum design, therefore, seeks a compromise between acceptable rim
and spoke strength and stiffness (Gordon, 2004).
Although finite element analysis can be used to good effect to model a
wheel assembly and also mechanical tests exist confirming performance (Rinard,
2002), there are advantages also in taking an analytical approach (Hull et al., 2002)
as the significance of the many variables can more readily be seen. So the primary
objective of this paper is to establish an analytical expression for determining the
radial stiffness of an ideal spoked wheel in terms of the major defining parameters.
Idealised wheel geometry
The following analysis is based on an ideal spoked wheel as shown in figure
1. The wheel consists of the circumferential rim, the hub and a number of spokes, N
which connect as pin joints between the rim and the hub. The rim has a radius, R
and the width of the hub is 2d and so the angle, between the centre axis is given
by :
R
d
tan
(1)
4
To determine the wheel radial stiffness a downward load P is applied at the
hub and this is reacted by an equal force, P at the rim where the rim contacts with
the ground. The deformation of the wheel is the shortening of the distance between
the hub and the contact point of the rim with the floor.
The original length of the spokes when not under load is L and the length
when secured at the rim and hub and tightened and thus subjected to pre-tension is
cos
R
Lo
.
Force equilibrium
Now consider radial force equilibrium for half a wheel whereby all spokes
are pre-tensioned with tensile load, To and C is the circumferential rim force (see
figure 2)..
For N number of spokes (and with the top spoke aligned with vertical
datum) the equilibrium condition for the half wheel is
2/
2/
0coscos2
i
TC
(2)
in which the sum is extended over all the spokes anchored to the half rim. So, if the
total number of spokes of the wheel is N, the number of spokes per angle unit is
2/N
and the sum may be evaluated as follows
N
d
n
i
cos
2
cos 2/
2/
2/
2/
(3)
which is acturate for most practical cases. For example, if there are 16 spokes, the
sum has a value of 5.027 whereas the
/N
approximation gives 5.093 indicating
an error of just 1.3 %.
Consequently, the hoop compression of the rim caused by the pretension of
the spokes is
5
2cos
0
NT
C
(4)
from which the relationship between the extension of the spokes
L
due to their
pretension
0
T
and the contraction of the radius
R
of the wheel rim due the hoop
compression can be easily found.
Effectively, L being the original length of a spoke,
S
E
the modulus of
elasticity and AS its cross section,
SS EA LT
L
R
LLL 0
0cos
(5)
and the radius of the wheel rim, with a cross section
R
A
and a modulus of elasticity
ER, will be reduced by an amount
L
E
E
A
A
N
EA
LNT
EA
CR
R
S
R
S
R
RRRR
2
cos
2cos 2
2
0
(6)
As the rim cross sectional area is typically about 30 times greater than the
spoke cross sectional area, because the rim is usually made from an aluminium
alloy whereas the spokes are from steel, in the case of a wheel having 16 spokes and
taking
97.0cos
means that :
LR 25.0
(7)
Equation (7) describes the stiffness of the wheel rim with respect to the spoke
tension and indicates that the variation of the radius of the rim and the extension of
the spokes are of the same order of magnitude.
However, this reducing of the radius of the rim must not be accounted for
when analysing the stiffness of the wheel, for it takes place when the wheel is being
built, previously to its use and loading. Nevertheless it was studied to illustrate how
the spokes and the rim become a joint structure.
6
Spoke contribution
To study the radial stiffness of the wheel it will be assumed that the hub
supports an in-plane load P, which causes a radial displacement a of the hub. The
aim of this analysis is to establish a relationship between a and P in order to deduce
the stiffness.
In this section only the displacement aS of the hub resulting from the strain
and the deflection of the spokes is going to be calculated. The displacement aR of
the hub due to the distortion of the rim is calculated in the following section and
then added to aS.
Figure 3 shows the hub loaded and displaced aS at the centre of the rim, with
only one spoke shown for clarity but the calculations account for all spokes.
When the load P is applied on the hub it is supported by all the spokes, each
of them being subjected to a tension Ti and stretched to a length
coscos iS
iaR
L
(8)
according to figure 3.
Then the fraction
i
P
of the total load P assumed by each spoke is
iii TP
coscos
(9)
the tension of the spoke being worth
cos
cos
coscos 0iSSSiSSS
ia
L
EA
TL
aR
L
EA
T
(10)
after substituting the pretension
0
T
from equation (5).
Consequently the load assumed by each spoke is given by
iS
SS
ii a
L
EA
TP
2
0coscoscos
(11)
7
with which the total load may be expressed as
2
0
2
2
0
0
1coscoscos iS
SS
i
N
iia
L
EA
TPP
(12)
In this equation both sums are extended over all the spokes anchored to the
rim and to the hub. So, if the number of spokes is N, there will be N/2
spokes per
angle unit, and the two sums can be calculated as follows:
0cos
2
cos 2
0
2
0
d
N
i
(13)
and
2
cos
2
cos 2
2
0
2
0
2N
d
N
i
(14)
When these results are put into equation (12) it is obtained that
P
ENAL
a
SS
S2
(15)
which is the spoke contribution to the radial distortion of the wheel.
Equation (15), shows effectively the proportionality between the distortion
aS and the load P and defines the stiffness of the wheel relative to the spokes as
L
ENA
KSS
S2
(16)
where the influence of the count of spokes and of their cross section and modulus of
elasticity as well as the influence of the size of the wheel are quantified.
At this stage it may seem surprising that aS does not depend on the
pretension of the spokes. However, this is so due to the fact that all the spokes
anchored to the hub, and pulling from it all around, experiment a tension equally
increased by such a pretension
0
T
. This is shown if the result of equation (15) is
taken into equation (10) yielding that
8
ii NP
TT
cos
cos
2
0
(17)
and explains why the magnitude of the pretension of the spokes does not influence
the displacement
S
a
of the hub. However it is noted that the above calculations have
been carried out on the assumption that the pretension of the spokes is such that
they are kept in tension all the time.
Equation (17) also shows that the spokes in the upper half of the wheel, for
which
2/2/
i
(see figure 3), are tensioned beyond the pretension when
the load P is applied, whereas the spokes in the lower half of the wheel have their
net tensile load reduced. The amount by which this occurs is due to spoke and rim
relative stiffnesses and is studied in the next section.
Rim contribution
The wheel rim, when loaded, will experiment bending due to the reaction of
the floor together with all the spoke tensions, which brings about another
contribution aR to the shortening of the distance between the hub and the contact
point of the wheel with the floor. Evidently, this must be taken into account when
calculating the stiffness of the wheel.
The approaching of the hub, upon which the load P is applied, to the lowest
point of the rim, where the reaction P exerted by the floor acts, is due to the bending
of the lower half part of the rim. This part of the rim is supported by the upper half
and is subjected to the tension
i
T
of the spokes anchored to it and to the reaction of
the floor P, as represented in figure 4.
Then the deflection
R
a
of the rim at the lowest point may be calculated by
deriving the strain energy of the bent half part of the rim, by using the Castigliano´s
theorem (Hearn, 1999, and Ryder, 1983).
Furthermore, accounting for symmetry reasons, the bending of the half rim
is going to be studied by considering only a quarter of the wheel rim, as shown in
figure 5, which supports half the reaction of the floor
0
2/ PP
, the tension
i
T
of
9
the spokes anchored to it and the hoop compression
0
C
as well as the bending
moment
0
M
exerted by the rest of the wheel rim at the base.
Consequently, the upright deflection
R
a
at the base of the rim is obtained
using Castigliano´s theorem from
0
P
U
aR
(18)
where U is the strain energy of a quarter of the rim.
The strain energy stored in a quarter of the rim can be calculated from
ds
IE
M
U
RR
2
2
(19)
where M is the bending moment in each section of the rim and
R
I
its moment of
inertia, and the integration is computed between the limits of the quarter rim
2/R
.
This calculation can readily be performed for a wheel having N number of
spokes for the following conditions:
1.- the quarter of the circle is divided into N/4 segments (see figure 5) with
spokes specified from the bottom (as 1, 2, ... j, etc) each having an arc
length 2
R/N between consecutive spokes;
2.- in each segment the bending moment value
j
M
is taken to be the value at
the central point.
Based on these assumptions the strain energy for the quarter of the rim can
be expressed as
4/
1
2
N
jj
RR
M
INER
U
(20)
In this simplified expression, every moment
j
M
can be written as
),,,( 000 ijj TMCPMM
(21)
10
from figure 5, and thus equation (20) represents the total strain energy of the quarter
of the rim as a function of the external loads
0
P
,
0
C
and
i
T
and of the external
couple
0
M
),,,( 000 MTCPUU i
(22)
This now enables Castigliano´s theorem to be applied. Effectively, the
upright deflection at the lowest point of the rim will be given by
4/
100
2
N
j
j
j
RR
RP
M
M
INER
P
U
a
(23)
whereas the horizontal deflection and the angular rotation at this point, which must
be null for symmetry reasons, will be given by
02
4/
100
N
j
j
j
RR C
M
M
INER
C
U
(24)
and
02
4/
100
N
j
j
j
RR M
M
M
INER
M
U
(25)
Now, if each bending moment
j
M
is substituted from equation (21) and the
tension of every spoke is taken as
0
T
, the last three equations (23), (24) and (25)
allow to express the upright deflection at the lowest point of the rim as a function of
the load
P
and of the pretension of the spokes
0
T
),( 0
TPaa RR
(26)
The deflection aR determined in this way accounts for the bending of the rim
due to both the load P and the spoke pretension T0. It is obvious that only the term
corresponding to the load P must be accounted for when determining the stiffness
of the wheel rim, since the deflection caused by the spoke pretension will occur
11
when the rim is being mounted as a joint structure and will have already been
performed when the loading of the wheel takes place and the stiffness is being
defined.
The whole procedure to calculate the rim contribution to the deformation of
the wheel is going to be throughout illustrated in a particular case.
16 spoke wheel rim
In this section the rim contribution to the displacement of the hub towards
the contact point of the rim with the floor, in a wheel with N=16 spokes, is worked
out, as an example of how it can be carried out in any case and in order to analyse
how it depends on the different variables which conform the rim.
The bending moments for the respective segments between consecutive
spokes of the considered quarter wheel, as shown in figure 5, are as follows:
00101 cos1sincossin M
N
RC
N
RT
N
RPM
(27)
002102 3
cos1sincos
3
sincos
3
sin M
N
RC
N
RT
N
RT
N
RPM
N
RT
N
RT
N
RT
N
RPM
sincos
3
sincos
5
sincos
5
sin 32103
00 5
cos1 M
N
RC
N
RT
N
RT
N
RT
N
RPM
3
sincos
5
sincos
7
sincos
7
sin 32104
004 7
cos1sincos M
N
RC
N
RT
Substituting these values into equation (23) gives the deflection
R
a
N
M
N
M
N
M
N
M
INER
a
RR
R
7
sin
5
sin
3
sinsin
24321
2
(28)
12
whereas equations (24) and (25) reduce to
0
7
cos
5
cos
3
coscos 4321 N
M
N
M
N
M
N
M
(29)
and
0
4321 MMMM
(30)
Now, if N = 16 and
0
TTi
, equations (27) are simplified as follows :
00001 01921.0cos19509.019509.0 MRCRTRPM
00002 16853.0cos75066.055557.0 MRCRTRPM
(31)
00003 44443.0cos58213.183147.0 MRCRTRPM
00004 80491.0cos56292.298079.0 MRCRTRPM
Then equations (29) and (30) represent a simple system from which the
hoop compression
0
C
and the bending moment
0
M
are directly obtained in terms
of the load
0
P
and of the pretension of the spokes
0
T
as follows:
cos98247.293771.0 000 TPC
(32)
and
cos20118.030384.0 000 RTRPM
(33)
Afterwards, taking values (32) and (33) to expressions (31) gives
cos06338.012676.0 001 RTRPM
cos04684.009370.0 002 RTRPM
(34)
13
cos05545.011088.0 003 RTRPM
cos03888.007782.0 004 RTRPM
Finally, by substituting values (34) in expression (28) and
2/
0PP
, it is
obtained that
cos02163.002160.0
80
3TP
IER
a
RR
R
(35)
where the two terms of the deflection of the rim appear. As it was said before only
the term due to the load P is accountable when determining the stiffness of the
wheel.
Consequently, the stiffness relative to the rim, when it has 16 spokes is
given by
3
06786.0 8R
IE
KRR
R
(36)
Radial stiffness of the wheel
Now the total displacement a of the hub caused by the in-plane load P may
be expressed by adding
S
a
and the corresponding term of
R
a
RS
RS
RS
RS KK KK
P
K
P
K
P
aaa
(37)
in which the stiffness of the wheel (as a structure comprising rim and spokes) is
computed as
S
R
R
RS
RS
RS
W
K
K
K
KK KK
KK
K
1
11 1
(38)
14
In the case of a wheel having 16 spokes, substituting equations (16) and (36)
into equation (38) yields the result
RRSS
W
IE R
EA L
K3
06786.0
8
(39)
This equation quantifies the contributions of both the spokes and the rim, in
terms of their geometry and materials, to the stiffness of the wheel.
If, for example, the spoke stiffness is significantly greater than that of the
rim, such that
SR KK /
is small then the overall wheel stiffness is dominated by the
less stiff rim. This can be seen from equation (38) by eliminating the KR/KS ratio
and leaving KW ---> KR.
Pretension of the spokes
When studying the spoke contribution to the stiffness of the wheel, the
length of every spoke, after the wheel is loaded, was named
i
L
and expressed in
equation (8) relative to
cos/R
, which is the length the spoke had reached after
being anchored and fixed between the hub and the rim, with a pretension
0
T
.
The spokes situated below the hub, for which
2/
i
(see figure 3) and
cos/RLi
, experiment a shortening when the wheel is loaded and so a
reduction of their tension, from the pretension
0
T
to
0
TTi
, according to equation
(17). The biggest shortening corresponds to the spoke at the lowest position and is
worth, from equation (15),
cos88cos P
EARP
EA L
a
SSSS
S
(40)
when the number of spokes is 16.
Also, the bending of the low half part of the rim due to the reaction of the
floor and to the tension of the spokes anchored to it causes an additional shortening
15
of these spokes and the subsequent reduction of their tension. This shortening is
maximum at the lowest position where it is worth [(see equation (35)]
cos8
06786.0
cos
3P
IE R
a
RR
R
(41)
again, when the number of spokes is 16.
It is important to recognise that the developed theory assumes that spokes
remain in tension at all times. This is because a spoke is incapable of supporting a
significant compressive load due to its high slenderness (that is length to diameter
ratio) thus making it prone to buckle. This means that it would have been incorrect
to have assumed that a spoke could support any appreciable compressive load and
so means that spokes must remain in tension at all times. This leads to the
requirement that the axial strain extension resulting from pre-tensioning needs to
exceed the greatest shortening that a spoke will experience – which is when passing
through their lowest position. Therefore, based on the 16 spoke wheel examples, the
following condition must be met [see equations (40) and (41)]:
cos8
06786.0 3
0P
IE R
EAR
EA LT
RRSSSS
(42)
from which the minimum pretension the spokes need is deduced
8
06786.01 2
0P
IRA
E
E
T
R
S
R
S
(43)
This will ensure that all the spokes are always tensioned, whatever their
position within the wheel may be, which is the most convenient condition for the
stability and strength of the wheel.
Maximum tension of the spokes
Considering that the spokes in the upper half part of the rim are not as
highly influenced by the bending of the lower half part, equation (17) is valid for
16
them and may be used to calculate their tension, which depends on their position
within the wheel. Evidently, the maximum tension occurs in the highest spoke, for
which
0
i
, and is worth
cos8cos
200max P
T
NP
TT
(44)
if the number of spokes is 16. Then the necessity for the tension never being
negative makes condition (43) unavoidable and therefore
max
T
8cos
1
06786.01 2P
IRA
E
E
R
S
R
S
(45)
This result does not give the tension of the highest strained spoke but its
minimum value as long as the pretension ensures that no spoke will be in
compression. In fact, the maximum tension the spokes will be subjected to depends
very much on the pretension
0
T
they are provided with under condition (43).
Numerical applications
It is interesting to apply the theoretical results so far developed to some
specific cases so that the significance of individual contributions can be seen. The
examples considered are taken from Chandler (2002) and correspond to three
commercially available wheel models, namely the Mavic Open Pro, the Shimano
WH-6500 and the Rolf Vector Pro as shown in figure 6. Their structural properties
are given in table 1.
Although the actual wheels are fitted with different numbers of spokes and
with different mounting arrangements, in this work the three rims were assumed to
have 16 spokes with a length equal to the radius of the rim,
350 RL
mm
(
1cos
), according to the idealised model of figure 1. In this way the results will
enable direct comparisons to be made. Also, in the three cases the rim material was
aluminium alloy (
70
R
E
GN/m2), whereas the spokes are from steel
17
(
200
S
E
GN/m2). The diameter of the spokes in all cases is taken as 2 mm
(
S
A
mm2).
Using this data the radial stiffnesses for spokes and rims were obtained
using equations (16), (36) and (38) and results are given in table 2. These results
emphasize the significant differences in the magnitudes of the spoke and the rim
stiffnesses and thus their contributions to the wheel as a structural assembly of the
two elements.
Table 3 presents the minimum pretension loads of the spokes for the three
cases, as calculated from equation (43), alongside with the maximum tension the
spokes will be subjected to, as calculated from equation (45). Both the pretension
and the maximum tension are given relative to the load applied on the hub.
General discussion
Although this analytical study of a spoked bicycle wheel is not exhaustive,
the analysis has established some important findings regarding the contributions
made by the rim and the spokes to the structural behaviour of a wheel.
In this work the effect of axial load distribution in the spokes and the
bending of the rim are combined to establish the radial stiffness of the wheel. It is
found that the results of this analysis are of the same order as those published by
Chandler (2002) by Hopkins and Principle (1990) and by Grignon (2002), which
suggests that the values are of the right order of magnitude.
The study has found that, in general, the system of spokes is much stiffer
than that of the rim and so the rim stiffness largely dictates the wheel radial
stiffness. This is particularly evident when studying equation (38) which shows how
the lower value of rim stiffness dominates the wheel stiffness when the system of
spokes have a stiffness an order of magnitude greater. It is interesting to observe
that modern optimal wheel design is moving towards wheels having much stiffer
rim cross sections with fewer spokes. For the radial stiffness of such wheels, which
have a wider spoke spacing distance, to compare with traditional multi-spoke
wheels, it is only possible when the cross section is much stiffer in bending.
In table 2, and with the help of equation (38), it can be deduced that
significantly changing the stiffness of the spokes will have little effect on the
general stiffness of the wheel. Consequently, reducing the number of spokes is
18
considered desirable as long as the wheel remains stable and so rim bending rigidity
becomes of critical importance. It is interesting to observe how the Rolf Vector Pro
rim despite having a smaller cross section with respect to the Shimano WH-6500
rim, and thus less weight and less material usage, has an improved stiffness of the
wheel due to its increased moment of inertia (see tables 1 and 2).
In addition, if the rim has a greater bending stiffness, spoke pretension need
not be so great thus permitting a lower maximum tension. This is because the stiffer
the rim, the lower the bending deflection in the bottom half of the rim and the
smaller the spoke contraction necessary with a lower pretension [see equation (43)].
Consequently with a lower pretension load when the wheel rotates half a turn and
the lower spokes come to the upper half part of the wheel they will not be placed
under such high tension [see equation (45)].
However, the rim moment of inertia cannot be increased indefinitely as
there exists a limit to the number of pre-tensioned spokes possible and so a
compromise is necessary for an optimum design to be achieved.
Conclusions
This analytical study has helped quantify how the spokes and the rim inter-
act with each other and work together when assembled to form a wheel and
subjected to a radial load. The work has taken into account both the bending
stiffness of the rim section and the axial tensile stiffness and preloading of the set of
spokes in determining a wheel’s radial stiffness.
It was deduced that achieving an optimum wheel design, in terms of wheel
radial stiffness, necessitates making a compromise between maximising rim cross-
section bending stiffness (which permits greater distance between successive
spokes) and having fewer spokes. Because there are many spoke and rim defining
parameters, many having conflicting effects, achieving an optimum wheel is a
complex process and so analytical equations have been developed to help simplify
the design optimisation process.
Pretension of the spokes is an essential part of achieving an efficient wheel
and the developed theory has enabled the minimum possible magnitude to be
determined so that spokes always remain under tension throughout the wheel
rotation load cycle.
19
References
Brandt, J., The Bicycle Wheel, 1993, Avocet, Palo Alto, California.
Chandler, M., An Investigation of Bicycle Wheel Rim Design, Final Year
Dissertation 2002, Department of Mechanical Engineering, University of Bath.UK
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20
Figure captions
Figure 1.- Idealised spoked wheel: the spokes are anchored to the rim and to the
hub. The load is applied on the hub.
Figure 2.- Half wheel rim supporting the tensions of the spokes fixed to it and
the hoop compression.
Figure 3.- When the external load P is applied on the hub it is displaced aS,
and so a spoke, whose pretension was T1, is deflected and enlarged
iS
a
cos
, while its tension becomes Ti.
Figure 4.- The wheel rim is bent by the reaction P of the floor. The deflection
at the contact point aR is the rim contribution to the radial distortion
of the wheel.
Figure 5.- Quarter of the rim supported by the rest of the rim at section A and
subjected to the tension of the spokes anchored to it and to half the
reaction of the floor. The action of the rest of the rim at the bottom
(
0
C
and
0
M
) is considered also as an external load.
Figure 6.- Different rim cross sections.
21
Rim
Mavic Open Pro
Shimano WH-6500
Rolf Vector Pro
Cross-Section Area
R
A
(mm2)
81.9
96.6
95.1
Moment of Inertia
R
I
(mm4)
4090
7670
8930
Table 1: Rim structural properties.
22
Rim
Mavic Open Pro
Shimano WH-6500
Rolf Vector Pro
Stiffness due
to spokes
S
K
(MN/m)
14.362
Stiffness due
to rim
R
K
(MN/m)
0.787
1.476
1.719
Resultant
Radial Stiffness
K
(MN/m)
0.746
1.338
1.535
Table 2: Radial stiffness of wheels.
23
Rim
Mavic Open Pro
Shimano WH-6500
Rolf Vector Pro
Pretension
0
T
2.41 P
1.34 P
1.17 P
Maximum Tension
max
T
2.53 P
1.47 P
1.29 P
Table 3: Spoke pretension and maximum tension, P being the spoke total load.
