Transcript
5.
EFFECTS OF ACCESSORIES, TYRES AND MACHIM MODIFICATIONS ON MOTORCYCLE DYNAMICS
5.1
ACCESSORIES
5.1.1
FairinEs
A fairing is a structure added to
a motorcycle to nake it
aerodynamically smooth and streanlined. The fairing affords a degree of protection
to the rider from wind and rain
generally makes for more comfortable touring. have
fairings
fittedto reduce
and
Racing motorcycles
the d r a g coefficient and hence
improve the top speed capability. Very
few motorcycles are sold
with fairings as original equipment, and it is generally left to the motorcyclist to choose and fit the fairing of his choice.
A
fairing can be mounted to the front forks, in which case it will move
with
the
steering, or 3e attached i t can
of the motorcycle
to
the nain
frame
s o that the steering assembly moves
independently of it,
There is evidence (Batten, 1979; Weir et al., 1978; Cooper,
1974) to suggest that fork-mounted fairings can reduce the weave or wobble mode dampingto the extent that at speeds in excess of 100 k m l h a danperouslv large oscillation can occur.
Batten
(1979) stated this was the experience o f the West Australian Road Traffic Authority withtheir Patrol Motorcycle, a Honda 750, fitted with a fork mounted fairing. Tests conducted by that Authority found that the addition of a steering damper virtually elimj.nated the wobble phenomenon with the fork-mounted fairing.
A frame-mounted Ealring tested did not cause any vibration problems, and there was no need for a steering damper with this design. Batten
also
conducteda questionnaire
1000 single-vehicle motorcycle accidentsin the
period1976, 1977 and of partof 1978.
8?
survey
of
riders
NestAustralia during The
total
number of
in
accidents
for
which
data
were
obtained405. was There
were76
accidents which involved motorcycles with windshields, representing 18.8% of the 405 motorcycles involved in single-vehicle He also found that 13.2% of the motorcycle population
accidents. in
West
Australiahad windshields, indicating a possible over-
involvement of motorcycles with
windshields
in
single-vehicle
These figures correspond to a 'relative risk' of 1.4,
accidents.
but as the size of the population-at-risk confidence limits cannot
be quoted.
sample was not given, Further, the relative
contribution of steeringassembly mounts versus frame-mounted fairings cannot he isolated.
Interestingly, the percentage of
the 405 single-vehicle accidents I n which wheel wobble was reported w a s 13.5% with no windshield,
and 18.416 with a wind-
shield.
Weir
etal. (1978) conducted a series
of
experimental
tests
to ascertain handling response and performance using a total of five different motorcycles selected to be representative of the range of machines currently available (see Section of this work included
4.2).
A part
a comparison of motorcycle handling
performance with and without fork-mounted fairings. They employed a steady-state turn test, a single-lane-change test and straight-line running. The steady-state turn test indicated that the
addition
of a fairing
had
some
effect on rider
subjective
ratings for the small motorcycle at low-and mid-speed. The middle-sized motorcyc1.e'~ subjective handling scores were largely unaffected by
the
fairings,
the ratings did not change.
and
with
the
very
large
motorcycle
The' single-lane-change manoeuvre
showed degraded riderratings at all speeds for the large motorcycle also
witha fairing. determined
for
Free-control stability properties were the
Honda
a fork-mounted fairing. 360 with
Analytical considerations established that the frequency of vortex shedding from a fairing at 100 km/h would be in the range 9 t o 15 Hz, which is near the wohble mode frequency f o r this motorcycle.
This could result in a forced vibration of the
steering assembly.
A series of high speed runs with the fairing
were made.
At a speed of about 135 km/h
at approximately 3.5 Hz occurred.
a sustained oscillation
It was not clear whether this
w a s a wobble or a weave; however the authors considered it to be
a low frequency wobble.
Cooper (1974) investigated the effects of aerodynamics on the terminal velocity, acceleration and fuelconsumption of a motorcycle.
It w a s found that significant gains in performance
occurred for road, road racing, and record-attempting motorcycles by addition of a wind tunnel designed fairing. Cooper
employed
the analytical model proposed by Sharp (1971) and included aerodynamic effects.
His nodel predicted thatthe addition of a
fairing slightly increased the
weave mode damping
decreased the wobble mode damping.
and slightly
Wirh the extensively stream-
lined record motorcycles an oscillatory instability at high speeds was experienced,and the analytical model wasa b l e to predict this behaviour. Motor Cycle Mechannzs (August lili8) published results of an investigationof the effect on stability of fitting mounted fairings.
The experiments
track and on an ordinary road surface. in
generalall the
fairings
tested
handlehar-
werecarried out ata test
The report concluded that were safe. However,
noneof
the fairings improved handling and none improved top speed. all cases
the
fairings
caused
no
major
hazards
at
In speeds to
110 km/h. One of the fairings evaluated upset the high speed handling of the Yamaha RD 250 considerably. the machine was still stable.
However at 110 km/h
The handling of a Honda C B 400 was
only slightly affected at speeds u p to 132 k d h through corners. 5.1.2
Luggage Xacks
Weir et al. (1978) compared the handling performance of five representative motorcycles with and without a rear-mounted load of approximately 10% of the Gross Venicle h'eight (GVK).
With the
s t e a d y turn and lane-change tasks oscillatory behaviour w a s
91.
up
observed in some cases.
A weave oscillation resultlng from the
CB 125 is shown i n Figure 5.1. rear load being added to the Honda This
isa near-limit
steady
turn 96.5 at k m / h o n a 122 m radius
turn (0.6 g lateral acceleration). divergent
in
yaw.
Withthe rear
The motion is slightly
load,
wobhle moti-ons couldbe
induced in the Honda CB 125 usin,e a steer torque pulse input(the handlebars
are
a bump). given
The results were strongly speed
5.2. dependent, as shown in Figure adding a rear
loadof 10% G V W could
The authors concluded that leadto weave
usually in near-limit manoeuvres when more heavily loaded.
oscillations,
suspension and tyres
are
Addition of a large rear loaddecreases the
wobble mode damping. With the steady-state turns, rider subjective ratings changed significantly when a 10% GVW rear load w a s a d d e d to the smaller motorcycles. The middle-sized motorcycles were less influenced by addition of a rear load.
For
the Norton 850, the rear 1.oad improved the low speed rating, and lowered its rating at high speed.
With the large Harley Davidson
HD 1200, the rear load decreased the
medium-speed rating.
Using
the single-lane-change test and an added rear load, the motorcycle suspension tendedto bottom in the second phase of the manoeuvre causinE rider controldifficulties and weaviny:.
The
load degraded rider ratings in the low and mid-speed ranges, with less noticeable effects at hiRh speeds.
Weave oscillations were
observed in straightrunning for the smaller motorcycles carrying an added rear load.
Slowing down or shifting the l~oad eliminated
these oscillations.
Wohble oscillations sometimes occurred with
larpe rear loads, prohahly due to the unloading effect on the front tyre and the resultantlower tyre side force coefficient.
Weir et al. ( 1 9 7 8 ) deliberately attempted to bring about weave oscillations, in order that their behaviour could be studied, by addin? a 45 kg rear load t o the Honda 360. represents 20% GVW
(includingthe
rider).
This
Extreme weave
oscillations at 100 km/h o n a 122 m radius curve occurred,as shown in Figure 5.3.
This manoeuvre corresponds to a lateral
acceleration of 0.6 g and a roll angle of 31".
92
On reduciny: the
T (ft-lbl Steer Torque
r ideg/sec Yad
I'eloclty
S ideg) Steer Angle
33
r (deg/sel Y an Velocity
+ (deg) Roll Angle
6 Idegl Steer Angle
Figure 5.2
Steer torque pulse giving rise to a wobble oscillation (Weir, Zellner ard Teper, 1978).
94
95
20
(ft-lb) -20 Steer Torque
S (deg Steer Angle U
(ft/st
Figure 5.4
Steer torque pulse on a motorcycle carrying a rear load (Weir, Zellner and teper, 1978).
96
rear load to 22.5 kg, no oscillation occured at this lateral acceleration. $1~0,with the 45 kg load, it was possible to set up a wobble
oscillation
in
straight-line
toraue pulse: an example c f t!:.i.s
5.4.
A wobble of about 5.5 iiz can
condition be
running a using steer
is
shown
in
Figure
seen in the traces.
Further testine. was done witha 22.5 k e mass added to the front assembly, 27C m m ahead of the steer axis. tests
sustained
weave
oscillations
were
In straight-line
observed,
steer torque pulse, in the speed range 3C to 103 knh.
following a
The basic
motorcycle without the mass could not be forced to weave in S
traight-line running.
Verma (1978) investigated the compliance of a luggage rack. The natural frequency of the rack with an 18 kg load was measured in the laboratoryand found to be around lO to13 Hz, close to the wobble frequency of the motorcycle used inVerma's work
(8Hz).
I t could
thusbe expected
that,
with a significant load
on the luggage rack, the wobble mode may be excited through sympathetic
oscillationsof the
rack
resulting
from
shocks or
wind buffeting.
5.2
PILLION PASSENGERS
From the accident literature reviewed in Chapter 2, it was noted that there is conflicting evidence on whether motorcycles with pillion passengers are over-involved in accidents, and
a
suggestion that they are more prone to single-vehicle accidents.
Weir
etal. (1976) included in tileir experimental program
tests to determine effects on the dynamic behaviour brought about by carrying a pillion passenger. The
results obtained were
generally similar to those induced by the addition of a 10% gross-vehicle-weight rear load (discussed in Section 5.1.2). Although a passenger may contribute 15 tc, 50% G V W (dependent on motorcycle size), the effects cannot be sinply extrapolated from
97
the dead-weight experiments, because complex body movements may act to damp the vehicle oscillations.
5.3
TYRES
Rice
etal. (1976) noted the importance of
tyre
characteristics
for handling behaviour of motorcycles. For a motorcycle negotiating a corner, side-ways forces at the front and rear tyre contact
areas
are
generated through negative
slip
necessary
for
equilibrium.
camber angle and sideslip angle. angles
are
developed
angle to maintain equilibrium in the differing
tyre
These
characteristics
is
in
forces
Positive or
conjunction
turn. clearly
are
with
The effect shown
in
camber
of Figure 5.5,
where a comparison of steer torque and steer angle requirements is
made
for
two
different
Davidson1200.
on a Harley tyres
The
replacement (alternate) tyre required far less steer angle to give equilibrium conditions at a particular lateral acceleration
(OEM) tyre. The than did the original equipment manufacturer replacement tyre generated more side force through camber mechanisms. The resultant steer torque requirements with the alternate tyre were far less, making the steering feel 'lighter.'
As part of his experimental program, Verma (1978) conducted runs aimed at measuring the influence of tyre condition on stability characteristics. Straight-line running tests at a range
of
set
speeds
to excite oscillations.
were
made
and
a
steer
torque
He intended to do three tests: one
pulse
with
new tyres, the next with a worn set of tyres and the thirdseries with worn tyres and an 18 kg rear load on the luggage rack.
The
data acquisition system failed to operate for the second set of tests, and so controlled data with tyres being the only variable were not available. tyres
it
was
During the course of the tests with the worn
found
that,
for
test
speeds of 80 k m j h and less,
sustained oscillations of noticeable magnitude occurred (Figure
5.6).
The addition of 18 k g rear load represents
vehicle weight.
6% gross
Weir et al. (1978) found that a 9% GVW rear load
98
was
used
I' I~qure 5.5
'lyre performance effscrs a Narley-Davidson 12'20motorcycle (Xics, 3avis and Kunkei, 1976) .
99
-
15.
U
W
v7 \
LrJ
W
0
v
> 10."
LU 2 W >
1 i
0 C
L
0 W
5."
n
3 kW
i L
S
c
0.7 10 SPEED OF MOTORCYCLE CMPHJ
Figure 5.6
Resonance due to worn tyres, and with a rear load included (Verma, 1978).
I
20
40
I
I
60 80 Forward Speed ( m p h )
I
1
100
Figure 5.8 First harmonic of tyre force compared with natural frequencies of weave and wobble modes (Venna, 1978).
10 2
on a Honda 360 destabilised the wobble node.
The strong wobble
oscillations encountered by Verrr.a were possibly not entirely due to the condition of the tyres. tyres on a flat bed
However Verma tested theworn
tyre t e s t rnzchine and
found
the
side
forces
generated eitlrcr througti side slip or camber showed periodic variations. Thj.s
is shown ir. Figure 5.7.
A harmonic analysis of
The frequency of side force
the variation was pcrfnrmed.
resnltindfror;. tyre^ non-unj~fornity
variation motorcycle
forwardspeed.
isa fur.ction of
Figure 5.8 shsus that
at64 k m l h (40
mph) the first harmonic of the tyre side force corresponds to the
wobble node nzturabfrecuency.
It
WBS
at this speed that the
strongest oscillations were noticed.
Keir
etal. (1978) pointed o u t that L y r e s have an important
influence on the motoriycle's dynarnic
behaviour, so that all of
their experiner-tal work w a s made with tyres of excellent conditior. and correctly Inflated.
However there were some runs
made with inflation pressure varintior. for the Honda 360 and the FLonda 125.
The results for these tests have not been reported.
Sakai, Kalnaya and Iljj~xa(19i9j ir-vestigated
the
effect of
inflatiuii 2ressure and wear or, the cornering stiffness and camber 6 tyres on a drum type sti.ffness of b o t h racinF a ~ stacclard
testing ~tachine. Figures
5.9
and 5.i3 r e s p e c t i v e l y s h o w
cornering stiffness and camber stiffness versus inflation pressure.
T h e racing tyre is seen to
inflation pressure than the ordinary tyre.
be more sensitive
to
Figure 5.11 shows the
effect of tyre width on camber stiffness and cornering stiffness. Cornering stiffness increases with p r e width, while only small changes in camber stiffness occur.
The variations of side force
and overturning moment with camber
ar:gle are affected
considerably by the amount and evenness of tyre wear, as shown in Figure 5.12 a n 2 5.13.
The results
of this work
clearly ir-dicate that large
variaiions in the tyred;;samic parameters car be effected by
B/ 0
1A)REAR TIRE 350-181PR. (BIRACIt6 T I E 325-18LPR. :20okg :50k d h
L L -
0
Figure 5.9
10 20 I.l? (kg/cm2
30
Variation of cornering stiffness pressure (Sakai, Kanaya Iijima, and
I .P.(kg/cm2 1
due to internal 1979).
Figure 5.10 Variation of camber stiffnes: due to internal pressure (Sakai, Kanaya ani? T < + i m a . 19791.
i0
r
L0l
TIRE -REAR TI RE 350-18LPR. 8 RIM : 1.85~1 RSURF. KNURLED. DRY.I W l 1.P LOAD V "
TIRE CON
1 -
l '1
OL
c
l CAMBER ANGLE (deg
Figure
5.11 Variation of cornering stiffness and camberstitfness due to size of tyre (Sakai, Kanaya and Iijima, 1979).
Figure 5.12
Vsriati.on of canher thrust due to w a r of tread (Sakai, Kanaya and IIJimzi+1979).
TIRE :REAR TIRE 350-laLPR RIM :1.85x18 RSURF :KNURLED.DRY. DRUM 1.P :20kg/cm2 LOAD : 200kg :50km/h V. TIRE. CON A
0
m
0
0
v
~ P J 0 m m
’ I
1
1
10 20 30 L0 50 60 CAMBER ANGLE (deg)
Figure 5.13
Variation of overturning moment due to wear of tread (Sakai, Kanaya and Iijima, 1979).
106
Figure 5.14
Outriggers used on motorcycles during tyre testing (Cycle VoTtd, August 1978).
4.55 ip
no 23.3 sq. ir!. a.32 4!4
,
tyres: a 16% variation overall for the 50 km/h stops and 26% for the 100 km/h stops.
Kokoschinski (1978 a, and b) performed tests on 22 different motorcycle
tyres
in
order to rate
themo n a comparative basis.
The program, whichwas reported in the German magazine Motorrad, included subjective assessment by expert riders at Nurburgring race track.
Six motorcycles of three different sizes
were used:
two Hercules K 125 S, two YamahaRD 400 and two B M W R 100 S.
The
small machines' behaviour was not influenced by different tyres, for two main reasons: firstly,the suspension bottomed well before limit tyre conditions were approached during cornering; secondly, not enough power was available forstraight-line limits to be reached. The
medium and large motorcycles were, however,
influenced by tyre type.
The tyres rated best were said to 'have
the common property that they noticeably stabilise the machine in fast straight-line driving and that they generate lateral forces in
curves
Some
of
such
the
that the limit of adhesion
tyres
rated
as good otherwise
was
never reached.'
were
saidto 'steer
into a curve with some reluctance', or to have 'a certain inertia when steering into alternate curves.'
The worst-rated tyres were
found to have 'little tracking stability' during initial braking and skidded at the rear during acceleration. did not
instil
much
confidence
in
Furthermore, 'they
their
adhesion
values
during
curve driving.'
Objective measurements of the tyres were made ata tyre factory.
These
measurements
showed
quite
wide
differences
quality control of tyre uniformity (radial and lateral deviations), the
speed
of
response
of
tyre
sideto force change
in slip angle, andthe steady-state side forces developed in response to sideslip and camber angles.
Generally, the ranking
of tyres accordingto these objectivemeasurements was consistent with the
subjective
size bikes.
ratings
on the medium obtained
and
larger
in
/5tapping Di:;tances. Front Brake Only.In Feel (Llsted in order 0 1 c o m b i n e d 30 a n d 60 rnph stopping distances) i
60 m p h / 30 rnph Goodyear. . . . . . . . . . . . . . . . . . . . . . ............32 .............................. 130 Carlisle. ........................................ 36 ........................... . l 4 5 l Mxhelin .......................................... 36 .............................. 146 i C h e n g Shin. .............................................. 38 ............................. 14E Continental ............................................ 36 ............................. ..l50 35 .................................. 154 Nankang ............................................................ 152 Dunlop. ................................................................ 38 ...................................... 37................................... 155 Pireili..................................................................... 35. ............................ 164 I R C ................................................................ 37.. ....................... 164 ’ Y o k o h a m a ...................................................... ” Avon ......................................................... 36. .......................... 1 0 1 Bridgestone .................................................... 37.............................. 171 38 ......................... 176 1 Nitto ..............................................................
,
I
1
! ~
The Cycle W o r l d and
Motorrad
tests
showed
that
different
brands of tyre lead to a wide rangeof ratings of 'confidencein tyre', 'degree of control' and
This confirms the
s o on.
conclusions from mathematical simulations of handling behaviour that
tyre
characteristics
play
an
important
and
subtle
role
the machine's behaviour. It would be desirable to be able to predict handling quality from a knowledge of the motorcycle and tyre characteristics. The present state of knowledge is inadequate for this, however. the mechanics
of
tyre
Further research is required into
force
generation
and,
indeed,
into
what
constitutes 'good' handling behaviour.
5.4
MACHINE MODIFICATIONS
Motorcycle riders often show their desire to express individuality by modifying their standard look different from the rest.
motorcycle to make it
These modifications may include
improved engine performance, low handlebars, rear-set foot pegs and a fairing.
-
'Cafe Racer'
A motorcycle thusmodified is sometimes called a see Figure 5.17.
the owner may extend forward, bar'.
lowerthe
At the other end of the scale,
the front forks, shift the foot pegs
seat
and
instal
These machines are called
a
pack
rack
called 'sissya
'Choppers' (Figure
5.18).
Motorcycle dynamic characteristics are particularly sensitive to the geometry of the steering assembly, and
licensing
so
authorities in Australia do not permit extension of front forks (The state of Queensland does not permit any
beyond 250mm. modifications).
Weir (1972) attempted to determine the effect o n handling performance of changing motorcycle design configuration. He analytically variation.
compared
The
latter
a
conventional motorcycle with involved
increasing
frame
achopper and
fork
angle, extending forks, lowering the rider seating position, and changing the inertial properties of the wheels. The lacked experimental verffication. However,
112
comparison
he was able to
rake
in
Figure 5.18 A 'Chop2erised' motorcycle (&percycZe, November 1979) .
113
v X,, Hingle Line
I
Fork tiead
Frame Veck "-,--
-
"
@Upper
Body c.m.
0
-
.
/ /
Figure 5.19
Nominal chopper configuration (Weir, 1972).
conclude that fine tuning of a chopper chassis could result in a motorcycle kyith overall handiipg properties about the same
as the
basic^ corventional motorcycie, and witt improvedhigk.-speed
cruising characteristics.
The East important consideration with
frame tuniag was the provision of positi:~e trail under all Figure 5.19 shows
loading conditions,~both static and dynamic.
the machine anaiyzed, i i t h the di.mersion 'k' being the trail Weir coml~ents that the process o f chassis
mentioned above.
tuning to achieve good hmdiing is particularly complex because of the extensive coupling in the equations of motion and 'in view
of this corr.plexity and sensitivity, it is in some vays remarkable that standard and chopper motorcycles have evolved, and that they are commonly used by riders of all skill levels.'
5.5
CONCLUSIONS
Fairings
A li~nenr mathec!atical model of rr.otorcyclelateral dynamics which includes tne aerodynamic chrracteristics of a forkmounted fairing indicates that tie wobble mode damping is decreased at high s?eeds b y the preser.ce of a fairing. The frequency of vortex s>.edding front a fairing may also coincide with the h-obble 3cde natural frequency, thus exciting a resonact wobble oscilLaticn.
Field experience with police patrol motorcycles has shown
that fork-mounted fairings c a n indeed cause steering wobbles ,at speeds in excess o i 100 kmih. (iii) One
e~xperi~mentiounr -:hat
qual~ity
subjective ratings of handling
S e g r a d e d Sy the :resrnct were
of a fork-mounted
fairirg, especially for smaller ~10torcyc.les.
(iv)
Tests conducted bv a motorcycling nagazine, however, did not reveal an? rr.ajor problems witt: fork-nounted fairings,
except for a light motorcycle, and then only at very high speeds.
Loads __ (v)
Addition of a rear load of 10% Gross Vehicle Weight (GVW) can lead toweave oscillationsin near-limit manoeuvres.
(vi)
A pillion passenger has been found to influence the motorcycle dynamic behaviour similarly to the addition of 10%
GVW. (vii)
A flexibly-mounted rear luggage rack carrying a substantial load may cause wobble oscillationsdue to a coupling of the rack vibrations with the steering motions.
(viii) Weave mode instability may be induced by the addition of mass forward of the steering axis.
(ix)
The deleterious effects fairly
of added loads generally require
extremeloadings or manoeuvres to become a signifi-
cant problem.
Tyres (X)
Tyre characteristics can influence the steering properties to a large degree.
'feel'
Large variations in tyre
dynamic parameters can result from differences in inflation pressure, method of construction and amount of wear. These are all
'in-use' tyre factors subject
t o wide
variations. (xi) 'Expert'
riders are able to rate different tyres
on a
subjective basis, with consideration given to their ability t o stabilise the machine in fast straight-line
116
driving, the level o f cornering adhesion limits, and their high-deceleration braking chsracteristics.
However, it is
not yet possible to predict motorcycle handling qualities from oh:jective measures of machine and tyre characteristics.
Plodifications
(xii) A 'chopperised' motorcycle can be made to handle much the same as a standard motorcycle. To do this, however, i t is necessary to pay careful measurements.
attentiont o the rake and trail
FINDINGS AND RECOMMENDATIONS FOR FUK'rHER RESEARCH
6.
6.1
ACCIDENT LITERATURE REVIEW
Motorcycling is popular for both commuting and leisure activit-
It is hazardous, however,i~ncomparison with automobile
ies.
driving, both in terms of relative frecuency and severity of accidents.
In the event of an accident the rider is at very
great risk, and usually makes contact with another vehicle or the ground.
The injuries suffered are usually severe.
The
typical
motorcycle
accident
involves 3 collision
with
another vehicle, usually an automobile, and in the urbanlsuburban environment. The motorcycle
i s generally travelling straight,
and a vehicle turns across its path.
Culpability largely rests
with the driver of the other vehicle.
In an accident situation Then braking is attempted, the rider typically
does
not
full braking capability of the
uti!ize the
A large accident study found that motorcyclists
motorcycle. applied both
front and rear brakes together in only half of the
cases in which braking was attempted. being
had
The
reduced
deceleration
achieved by riders results in increased impact speeds, and
thus accidents of greater severity than need be the case.
Motorcycle braki.ng performance usually deteriorates in wet weather and accident data confirm that riders are then at greater risk.
Perhaps partly as a result of this, wet weather riding is
greatly reduced and the magnitude of the accident problem is similarly reduced.
Xotorcycles have motior. instabilities that, when excited, are beyond the
capabilities of the rider to control.
However, they
are mostly higk: speed phenomena and, as most accidents occur within the 60 k n i h speed limit zones, these problems dc not appear to he of great concern.
l19
The effect of motorcycle handling characteristics on accident risk has not beenstudied, due in part to a lack of knowledge of appropriate ways to characterize handlingqualities. The most machine runni.ng wide common loss of control accident involves the on a turn.
The presence of a pillion passenger, or lack of
familiarity
withthe
motorcycle
single-vehicle accident. Modified
increases
the
likelihood of a
machines are apparently not
over-represented in accidents.
6.2
MOTORCYCLE BRAKING
The performance of disc brakes in wet weather deteriorates rapidly, as they suffer increased response time and require higher input force levels to achieve dry-brake deceleration levels.
The Transport Road
Research Laboratory, in conjunction
with Dunlop, havedeveloped a sintered metal pad which appears to overcome these problems.
A t this time only one motorcycle
manufacturer
is
(Kawasaki)
known to be
supplying
these
pads
original equipment.
Aspects of the testing requirements for motorcycle and moped No. 33, braking systems, contained in Australian Design Rule
are considered to be inadequate, as the brake environment in wet conditions is not well simulated. Linked brake systems provide front and rear brake application simultaneously, thus eliminating the problem of the rider using only one brake in an accident avoidance manoeuvre. Only one manufacturer (Moto Guzzi)
supplies
braking system. Investigations are performance
motorcycles
with a linked
recommended to assess their
undervarying conditions andwith riders of different
levels of skill.
Furthermore, a system which allows forvarying
levels of deceleration and the presenceor otherwise of a pillion passenger should be researched
as
Experimental
work has shown that antilock brakes provide
superior performance to standard brakes, particularly whenthe road surface is
slippery.
Several systems are at the prototype
development stage.
The ergonomics of the separate front and rear brake systems found on nearly
all
motorcycles
have
not
yet
been
subjected
scientific scrutiny. As the characteristics of these systems vary greatly from motorcycle to motorcycle, it is expected that such a study should lead to systems with more universal appeal, providing better deceleration performance.
6.3
STABILITY AXD HANDLING CHARACTERISTICS
A n a l y t i c a l s i m u l a t i o n s o f the notorcycle-alone and the rider/motorcycle system in variousmaneouvres have identified the major dynamjc modes of capsize),
the motorcycle (weave, wobble and
rider control strategies in making
a turn, and
pitchlweave coupling effects in high lateral acceleration cornering.Thesemodelsnowoffer
a fairly accurate
representation of the motorcycle dynamics. Further work is required with tyre models and rider representation. riderlcycle model. wou1.d
b e a valuable
A validated
tool to safely and
economically investigate the effects of a variety of motorcycle design parameters andmachine modifications. A n investigation into obstacle avoidance showed that
lightweight motorcycles did not performany better thanmedium heavy machi.nes. more distance
or
A rider with low skill required about i5 to 20%
to avoid the obstacle than skilled riders. These
tests also showed that a motorcycle should notbe considered more manoeuvrable than an automobile in obstacle avoidance. The oversteerlundersteer characteristic used to describe automobile handling has been investigated as a motorcycle handling paramcter. Riders PI-eferred a motorcycle with neutral to
l21
to
modest oversteer properties. They
also preferred a machine with
a well-damped, stable weave mode at high speed.
The results of
lane change experiments showed that riders prefer a motorcycle which begins to yaw initially rather than the first response being a change of roll angle. conclusions
have
been
However, only very tentative
drawn
about
desirable
handling
response
properties, and the study of motorcycle handling is in its infancy. Anecdotal evidence gleaned from the popular press suggests existence of problems such as high speed weaving, high speed wobbles, slow responseat low speed, self steering, and roll limits imposed by footpegs, mufflers and stand brackets. have a large influence
Tyres
on ratings of steering and handling
behaviour, and disc brake performance in wet weather is not regarded as satisfactory.
Further work is required
to quantify
these effects.
6.4
EFFECTS OF ACCESSORIES, TYRES AND NACHINEMODIFICATIONS ON MOTORCYCLE DYNAMICS
A fairing mounted on the forks can give rise to wobble oscillations at speedsin excess of 100 km/h.
This can be eliminated by
addition of a steering damper, or by mounting the fairing direct to
the
motorcycle
main
frame.
The
due to fitting a fairing isgreatest with
Addition
of10% G V W to
degradation
of
rider
rating
smallmotorcycles.
therear o f a motorcycle
weave instability during near-limitcornering.
can
lead to
A weight added
ahead of the steering axis may give rise to weave oscillations. A pillion passenger has a similar effect on motorcycle handling as addition of 10% GVW.
Motorcycle behaviour is strongly influenced by tyre pressure, condition and design.
A large variation in machine characteris-
tics is obtainable by altering the type of tyres fittedto it.
122
A 'chopper' motorcycle
with
extended
front
forks,
could be
made to handle much the same as a standard motorcycle, if proper attention w a s given to
tuningtile rake and trail
dimensionsof
the steering assernhlv.
6.5
RECOF~EIENIIATIONS FOR RESEARCH
In the field of hrakinc. stabilityand handling of motorcycles, a number o f areas requirinp researchhave been identified. The accident hraking
data
suggest
studies. It
that
is
highest
clear
that
priority
should be given
a r e not riders
to
utilizingthe
full^ hraking ca7acities of their machines. Although stability
and handl~ing
research
would
appear to have
lower
priority,
it
should be noted that very little is in fact known (in a scienti~fi.~ sense) about motorcycle handling.
Thus, it is
unlikely that accident investigators will have been able to make adequate judgements about the role of handling characteristics in accidents.
Specific research topics, arranFed roughly
in^ order of
priority, are a s follows:
The separate front 2nd rear hrake controlsfound on nearly
all^ motorcvcles have characteristics frorr machine
t o machine.
An
whichvary E-reatly
experimental study
to
ouantify these characteristics and to analyse the erfronomi.~
of riders capabilities
should he undertaken.
incontrolli.ng brakes
This should result in provision of
motorcvcle hrake systems in which riders have confidence and which
will
improve
their
utilization
of
the
braking
potpntial of their machines.
1.2
Lj~nkrd hraking systems have many advantages, mainly in t h a t thrv p r ~ v e n t the 11se of o n l y the rear brake in an
123
accident situation and hence maximise deceleration. Development of a v a r i a b l e p r o p o r t i o n i n g s y s t e m t o optimally distribute braking effort, based on deceleration or o t h e r w i s e o f a pillion
level and the presence
passenger, should be initiated.
The performance of such a
system with a range of brake and tyrelroad friction conditions,
and
with
riders of varying
skill,
should he
investigated.
1.3
Australian Design Rule
No.
3 3 - Motorcycle and Moped
Braking System hasbeen shown to assess wet weather hrake performance inadequately. The procedure should modified to incorporate amore which would
realistic
he
wettingtechnique
modelthe actual wet weather brake environment
more closely.
This
technique
should
he
the
of a subject
research project.
1.4
Antilock brakes are seen
to he an ideal solution
obtaining maximum deceleration with unskilled and when conditions are wet and slippery. this time they are
prohibitively
for
operators
Rowever, at
expensive,
and
are
available as standard equipment. Overseas developments in this area should br monitored.
2.
Stability and Handling
2.1
As yet, parameters which adequately characterise motorcycle handling quality have not been established. A combined experimental and analytical research program is required to identify optimum handling response characteristics for a motorcycle.
It can he anticipated
that a motorcycle which is matched
to
the control
the work load in capabilities o f the rider will reduce stabilizing and controlling the machine, thereby increasing his capacity to deal with traffic events.
This
should have a favourable influenceon accident statistics.
124
not
On completion of this fundamental work on motorcycle
handling, research into a number of important aspects of in-use behaviour could be approached on a rational basis.
For example, there is a need to:
(i)
Ouantify the
influence of tyre pressure, wear
on motorcycle stability and handling.
recommendations being established
(ii)
and design
This would lead t o
forusers.
Enable safe limits for carrying of load and passengers to be established.
(iii)
Measure the changes in characteristics arising from fitting variousdesigns of fairings, with different methods of attachment, and hence make recommendations.
(iv)
Conduct an accident study designed to measure the role of stability and handling characteristics inaccidents.
125
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___
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133
APPENDIX A
A. 1
DERIVATLOK OF SIMPLE NOTORCYCLE BRAKING EOUATIONS
The following derivations intendto show the effectof using front and rear. front only and rear onl~; brakes for decelerating a rnotorcyc1.e i n a straight line on
A.l.l
level surface.
Front ar.d Rear Brakes Applied Together
Kefrrring
FigureA.l, and assur.ing that
to
the
brakes
are
applied to the limit of available friction between tyre and road surface, eqrrili~brium conditions yield:
= n
Z’L X1
!:,(a + b) = mgh + mDh
-
where D is the deceleration
(A.2)
Let
= friction coefficicnt between
t r r e and road, then it
follows that: ,!l
=
U‘!
(A.4)
i
l35
X
Figure A.l
Basic dimensions of motorcycle, front and rear brakes appl.icd.
f
1.; Figure A.2
Nr
Motorcycle with front brakes applied.
136
A.2, A.4 and A.3 yields:
Substituting A.],
A.2.1
Front Brakes Applied Alone
Referring to Figure 4.2, it can be shown that: l:f
(A.7)
= -?D
S o ; substitutin? h.4 and A.1 into A.? yields:
n = A.1.3
Llgb/(l,
-
pi)
Kear Brake Ap?lied Alone
(A.9)
Using the data for sir motorcycles covering the range
from
lightweight commuter to heavyweight tourer (Rice et al., 19761, a graph of percentage of available deceieration obtained using
front and rear, front only and rear only Srakes versus tyrefroad friction coefficient was plotted and is shown inFigure 3.10.
137
Figure P.3
Motorcycle with rear brakes applied.
138
