In this paper a four-wheeled electric bicycle was in focus. We determined the coefficient of rolling resistance (Cr) and total power output (TPO) at five different tyre pressure levels and on three different road surfaces. Cr was estimated using riding velocity and power output and total power output was combined power output of the motor and the driver. The author assumed that the effect of tyre inflation level has an effect on Cr and on TPO but the analysis of the measured data didn't show significant difference while there was significant difference between the road surfaces. In the present study the mean change in Cr was 5,5% on asphalt, ~11% on fine gravel and ~8% on coarse gravel while former studies found higher differences on different road surfaces while the TPO data showed 4%, 3,5% and 4% of mean change on the same surfaces. The results didn't match with the results of former studies where the relationship of Cr and TPO with the tyre pressure was found to be curvilinear because the present results were closer to linear. The author hypothesises that role of the 150 kg transported weight, which is way higher than in other studies, and the unique structure affects the data more than assumed before.

1. INFLUENCE OF TYRE PRESSURE ON COEFFICIENT OF ROLLING
RESISTANCE AND TOTAL POWER OUTPUT OF RIDING A FOUR-
WHEELED ELECTRIC BICYCLE
Abstract
In this paper a four-wheeled electric bicycle was in focus. We determined the coefficient of rolling
resistance (Cr) and total power output (TPO) at five different tyre pressure levels and on three different
road surfaces. Cr was estimated using riding velocity and power output and total power output was
combined power output of the motor and the driver. The author assumed that the effect of tyre
inflation level has an effect on Cr and on TPO but the analysis of the measured data didn't show
significant difference while there was significant difference between the road surfaces. In the present
study the mean change in Cr was 5,5% on asphalt, ~11% on fine gravel and ~8% on coarse gravel while
former studies found higher differences on different road surfaces while the TPO data showed 4%, 3,5%
and 4% of mean change on the same surfaces. The results didn't match with the results of former
studies where the relationship of Cr and TPO with the tyre pressure was found to be curvilinear because
the present results were closer to linear. The author hypothesises that role of the 150 kg transported
weight, which is way higher than in other studies, and the unique structure affects the data more than
assumed before.
Introduction
During cycling the velocity and power output of the cyclist depends on the resistances
which deter the movement. A former study determined that approximately 90 % of the
total resistance is aerodynamic drag and the residual 10 % are the other resistances,
including the mechanical resistance of moving parts and the rolling resistance (2).
Because of its bigger proportion, the aerodynamic drag was in focus in many studies (14)
(10)(6). These results are true for road or track cycling, but in sports like mountain-biking
or when leaving the asphalt road the other resistances have more influence. In
mountain-biking the typical velocity is lower than in road cycling (11-14 m
/s on road vs.
5,5-8,5 m
/s off-road). Therefore considering the relationship between velocity and
aerodynamic drag, lower speed means lower drag. In off-road circumstances the rolling
resistance increases because the influence of the nature of the terrain and the
properties of the tyre have an effect as well. The rolling resistance defined as the
resistance against the wheel motion caused by the contact of the wheel of the bike and
the surface of the terrain. The rolling resistance is considered independent from speed
but the results of Faria et al. showed that its contribution to the total resistance
increases when the speed decreases (4). Bertucci et al. calculated the rolling resistance in
mountain-bike field as well as road conditions and determined that the proportion was
21 ± 4%, 35 ± 5% and 65 ± 7% of the total resistance on road, sand and grass sections,
respectively while the proportion of the aerodynamic drag was 8 to 35% depending on
the ratio of the rolling resistance. These values are different from the affore mentioned

2. 90-10 % ratio and it is shown that the rolling resistance is two to three times lower on
road than in other terrains(1). The rolling resistance (Rr) can be calculated as the
multiplication of the rolling coefficient (Cr) and the vertical force (Fv) which consists of
the transported mass and the acceleration due to gravity (m*g).
Rr=Cr*Fv 1.
Kyle and van Valkenburg determined that a little change in rolling resistance can
influence the performance in road cycling. In detail they showed that a 0.02 % decrease
of the Cr cause detectable positive changes in cycling performance (9).
As mentioned before, the main factors of the rolling resistance are the terrain and the
tyre. The resistance is generated at the point where the surface and the total area of the
tyre are in contact. During this contact the tyre shows a phenomenon called hysteretic-
loss which equals with the also mentioned Rr=Cr*F (mg) equation (2). The vertical force
consists of the mass of the bike and the rider while the value of the rolling coefficient
depends on tyre and wheel properties like wheel diameter, type, thread type, size and
inflation pressure of the tyre (11). Generally larger contact area induce greater resistance.
Therefore mountain-bike riders have to face greater rolling resistance than road bicycle
riders, because the diameter of the rim is smaller, the wider tyre size has larger contact
area with the surface and the inflation pressure is smaller in mountain-bike tyres (3).
Aside of these influencing factors the thread characteristics have an important affect as
well. Bertucci et al. compared a smooth and a knobby mountain-bike tyre in three field
surfaces (road, grass, sand) and found that the smooth tyre has 21+
/- 15 % less rolling
resistance than the knobby tyre, which means that rugged tyre surface cause higher
resistance, but in certain surfaces it ensures better grip (1). Grappe et al. investigated
among other the effect of inflation pressure on the rolling coefficient. They used five
different tyre pressure between 150-1200 kPa and found that Cr decreased by 62 %
between the extremes which ensured the assumption that the higher the inflation
pressure the lower the resistance (5). A conventional mountain bike tyre which was used
on the subjected four-wheeled bike in the present study has a recommended inflation
pressure of 30-50 psi (206,85-344,75 kPa) which ensures the best rolling efficiency (13).
Manufacturers recommend a maximum pressure of 65 psi (448,17 kPa). High tyre
pressure decreases the deformation of the tyre which means lower hysteretic-loss, but
decreases the gripping ability and increases transfer of vibrations from the surface which
can be even more inconvenient in higher velocities (7). Wilson et al. published an
investigation with this formula:
Popt=0.3 psi/kg ∑weight
(rider + bike)
2.
which can be applied to reach the best grip of the bike, which is good for maneuvering.

3. But experiences showed that it increases the rolling coefficient and therefore the
resistance as well (15). According to the rules of physics more resistance requires more
energy output from the cyclist and presumed that the bicycle is equipped with an
electric engine, from there as well. Recently electric bicycles are getting more popular
among customers and after the first pioneers many conventional bicycle companies
released their electric bicycles to the market. Whereas for the conventional bicycles the
rolling resistance affects the maximum speed achievable with a certain power for
electric bicycles the main resistances affect the range as well. An important issue for
electric bicycles is how to expand their range and how to estimate the residual range
which are the affecting factors. At first a higher capacity battery could be use, but bigger
battery has higher weight which again shortens the range. Also a low power
consumption motor could be use. Usually, the lower power output motors are smaller in
size and weight which is good considering the transported weight, but the performance
may not be enough to move the bicycle properly and in consequence increase the
power consumption. The range issue and its affects are mainly in focus of the studies
with electric bicycles like in case of the TUM QuadRad. Also, limited number of studies in
this field and of four-wheeled bicycles made this investigation a real challenge(17)(18)(19).
A former study has been conducted with a different but comparable prototype of a four-
wheeled electric bike on the same tracks which this investigation will use. During the
investigation among others the velocity and both the energy output of the motor and
the driver were measured with a smart device. The rolling resistance was calculated
using the measurement data. To the knowledge of the author four-wheeled bicycles
were rarely in the focus of former studies and there was no other investigation with
electric four-wheeled bicycle since the recent investigations in Technical University
Munich. In 2000. Zamparo et al. made a study about a four-wheeled recumbent bicycle
and found that the rolling coefficient is averagely 60% higher than in a case of an
ordinary road bike. The best performance times on 1, 5, 10 km distances were 8% longer
with the four wheeled bike than the subjects performance on a road bike on the same
tracks. The posture of the body of the driver was different and the bike was 28 kg while
the QuadRad weights 78 kg, which means that the recumbent bike may have lower
rolling resistance on certain surfaces and lower power requirements than the QuadRad
(16).
This investigation will follow the method used in former studies with the QuadRad with
a slightly different prototype design using the same evaluation methods and test tracks
under similar conditions. Therefore, the aim of the present study is to get new results for
the rolling resistance coefficient and the total power output with a modulated bike in
relation with different tyre inflations with the intention of a subsequent comparison
with the results of the former studies (8). The author hypothesises that the tests at
different tyre levels will show measurable and significant effect on the rolling resistance
coefficient and on the total power consumption. Additionally, different road surfaces will
show effect on these values as well.

4. Method
Subject
One male cyclist participated in the study. The age, weight and height of the person
were 33 years, 72 kg and 176 cm respectively. The subject was the author of the present
study.
Material
A QUADRAD Project four-wheeled electric bike powered by a Continental prototype
electric motor and equipped with on board display and control system was used in the
study. The total weight of the bike including all of the devices is 78 kg. Therefore the
transported mass with the driver is 150 kg. A Wiko Birdy Android 4.4.2 mobile phone
with an application called QUADRAD HMI recorded the raw data via bluetooth
connection with the on board system of the bike. The measured values among others
were velocity, energy output of the electric motor and power output of the driver. A
Garmin Edge 200 GPS device recorded the data of the location and the length of the test
and a Garmin Express software exported data into a Microsoft Excel file. The tyre types
on the rear 32 spokes classic MTB wheels were two Schwalbe Racing Ralph MTB racing
tyre (size:26x2.1; recommended tyre inflation 2-4 bar; 30-55 psi) and on the front
wheels of the same type were Continental Top Contact MTB tyre for roads (26x2.0;
maximum inflation 2,5-4.5 bar; 35-65 psi). The tyre pressure was set with a classic hand
pump for road bikes with a maximum inflation pressure capacity of 174 psi (12 bars).
Protocol
The tests were performed on three different surfaces, asphalt, coarse gravel and fine
gravel at five different velocities 5, 10, 15, 20, 25 km/h. The distance on each surfaces
was 650 m. The investigation was performed with five different tyre inflation pressures
which were chosen by the following: 1) ideal pressure of the tyres 50 psi (3.5 bar), 2)
ideal pressure +8 psi (0,5 bar)=58 psi (4 bar), 3) ideal pressure -8 psi (0,5 bar)=42 psi (3
bar), 4) ideal pressure +16 psi (1 bar)=66 psi (4,5 bar), 5) ideal pressure – 16 psi (1
bar)=34 psi (2,5 bar). The ideal pressure was chosen considering the maximal and
minimal recommended pressures of the tyres. The test on each surface took place on
the same track with determined start and end points. These test tracks were used in a
former tests with a similar prototype bike and because of an intention of a comparative
study between the two bikes, the subject used the same test tracks. The driver drove the
bicycle on each surface with each tyre pressure with every velocity in both directions
(1300 m with each velocity) and held a 30 s offset measurement session after every 650
m to isolate every measured part. The total tested distance was 292,5 km.
Statistics
The rolling resistance was calculated with the transformed equations using the
measured power and velocity data. The rolling resistance can be calculated by equation
1. The drag resistance can be calculated by:
Ra=0,5ρairACdVc 3.
where ρair is the air density and ACd is the constant effective frontal area and Vc is the

5. velocity neglecting headwind. The mechanical output can be calculated by:
Pext=RaVc+RrVc 4.
where Pext is the mechanical power output, Ra is the aerodynamic drag, Rr is the rolling
resistance and Vc is the velocity. This equation is transformed into:
Pext=0.5 ρairACdVc
3
+CrMgVc . 5.
which applied as a MatLab formula gave the figures of rolling resistance coefficient (Cr).
The raw data were cleaned of not used data and measurement errors. Subsequently
with a Microsoft Excel template designed for this dataset, the mean velocities and total
power outputs were calculated on daily and on tyre pressure basis on each surface.
These data were used in the calculation of Cr by MatLab software applying the above
mentioned formula. The formula was embedded into a Matlab script which analysed it
with a curve fitting algorithm. The correlation coefficients were determined for the
linear relationship between the tyre pressure and Cr, the tyre pressure and total power
output and between the surface, the tyre pressure and the Cr. Because of the numbers a
variables group factorial analysis of variances (ANOVA) and post-hoc Bonferroni test
evaluated the main variables. To use the ANOVA six assumptions have to accomplish. At
first the dependent variable should be measured at the interval or ratio level. Secondly
the independent variable has to consist of two or three more category and at third it's
not possible to be a relationship between the independent groups of observation. If the
data meets the first three assumptions, after the next three assumptions analyze by the
software. Assumption four states the outliers should be exclude while assumption five
determine whether the dependent variable is normal distributed on every independent
variable groups. Assumption six states the need of homogeneity of variances. Statistical
significance were set to P≤0.05. These statistics were performed with IBM SPSS
software.
Results
The differences in Cr on different tyre pressure and surfaces presented in table 1.
coloured with green the lowest and with red the peak values. The Cr was between
0,01324 and 0,01401 on asphalt, 0,01591 and 0,01722 on fine gravel and 0,01842 and
0,02007 on coarse gravel. In the present study. The Cr increased from the lowest to the

6. peak value by 5,5% on asphalt, ~11% on fine gravel and ~8% on coarse gravel. On the
asphalt surface the lowest value measured at 3,5 bar and the highest value measured at
3 bar tyre pressure. At the other three tyre pressures the difference was ~2,5 % between
0,01357 and 0,01393. On fine gravel surface the lowest value was at 3 bar tyre pressure
and the highest measured at 3,5 bar and the same measured on the coarse gravel. At
the other tyre pressures difference was 3,5% on fine gravel between 0,01601 and
0,01659 and 5,5%, between 0,01856 and 0,01961 on coarse gravel. The statistical test
indicated that there is no significant relationship between the different tyre pressures
and the changes in Cr at any kind of surface. On the other hand the tests indicated that
there is significant changes in Cr on different surfaces. The average change of Cr on each
surface is 5,5% in asphalt, 11% in fine gravel and 8% in coarse gravel.
Table 1. Cr on different surfaces at different tyre pressures
On figure 1. the results shows that as the road surface get even rough the mean Cr values
are getting higher. Every Cr value at a certain tyre pressure is higher from smoother to
rougher surface. This figure assured the result of the statistical test which indicated that
there are significant relationship between the surfaces and changes in Cr.
Figure 1. Cr on different surfaces at different tyre pressures
The differences in mean total power output (TPO) on different tyre pressure and
surfaces presented in table 2. and table 3. and 4. and 5. shows the mean TPO on certain
surfaces at different tyre pressures and velocities all coloured with green the lowest and
with red the peak values.

7. Table 2. Mean total power output on different surfaces and at different tyre pressures
On asphalt surface the mean values of TPO were between 148,63 and 155,2898 W. The
percentage difference between the lowest and the peak value is ~4%. The lowest value
measured at 4,5 bar the peak value at 3 bar. Between the other tyre pressures the
difference was ~2%. Table 3. shows that on different velocities the four out of five peak
TPO measured at 3 bar and one at 2,5 bar and three of the lowest values measured on
4,5 bar and two at 3,5 bar.
Table 3. Mean total power output on asphalt at different tyre pressures and velocities
On fine gravel surface the mean values of TPO were between 166,942 and 172,6752 W
(table 2.). The percentage difference between the lowest and the peak value was ~3,5%.
The lowest value measured at 2,5 bar the peak value at 4,5 bar. Between the other tyre
pressures the difference was less than 1%. Table 4. shows that on different velocities the
two out of five peak TPO measured at 3,5 bar at the lowest 5 and 10 km/h velocities. At
15 km/h the peak value was at 4,5 bar, at 20 km/h was at 4 bar and at 25 km/h it was at
2,5 bar. In the case of the lowest values at 5 km/h the measured lowest value was at 4
bar, at 10 and 15 km/h it was at 3 bar, at 20 km/h it was at 3,5 bar and at 25 km/h it was
at 2,5 bar.
Table 4. Mean total power output on fine gravel at different tyre pressures and velocities
On coarse gravel surface the mean values of TPO were between 183,1414 and 191,254
W (table 2.). The percentage difference between the lowest and the peak value was

8. ~4%. The lowest value measured at 4 bar the peak value at 3,5 bar at the two extremes
of the pressure line. Between the other tyre pressures the difference was ~2%. Actually
comparing the mean TPO in table 2. of asphalt and fine gravel they show almost the
same values. Table 4. shows that on different velocities the peak TPO at 5 km/h was at
4,5 bar at 10 km/h and 15 km/h the peak value was at 3,5 bar, at 20 km/h was again at
4,5 bar and at 25 km/h it was at 3 bar. In the case of the lowest values at 5 km/h and 10
km/h the measured lowest value was at 4 bar, at 15 km/h was at 4,5 bar, at 20 km/h it
was at 2,5 bar and at 25 km/h it was at 4 bar.
Table 5. Mean total power output on coarse gravel at different tyre pressures and velocities
The statistical test indicated that there is no significant influence of the investigated tyre
pressures on the total power output on each surface and no influence was experienced
on daily basis comparison on each surface as well. Figure 2. shows the mean TPO levels
on the surfaces at different tyre pressures. The average mean TPO change on each
surface is 4% in asphalt, 3,5% in fine gravel, and 4% in coarse gravel. Average TPO
change between asphalt and fine gravel is ~10,5%±3%, between asphalt and coarse
gravel is ~20%±2% and between fine gravel and coarse gravel is ~9,5%±2% comparing
them in all of the tyre pressures.
Figure 2. Mean TPO on different surfaces at different tyre pressures
Discussion

9. The results in the present study indicated the effect of tyre pressure on Cr is not
curvilinear as former studies stated. As figure 3. shows the average Cr values on asphalt
were start and end on higher degrees and the lowest value provided by the middle
measured tyre pressure level, at 3,5 bar. The other two surfaces show the opposite
process. The tyre pressure extreme rates were smaller and the peak value reached at the
middle measured tyre pressure level, at 3,5 bar, where the asphalt provided the lowest.
These values provided a wave shaped graph when it's illustrated. Grappe et. al.
Investigated Cr values on five different tyre pressures and he found curvilinear
relationship between Cr and the tyre pressure levels. Cr was inversely and hyperbolically
related to the tyre pressure. That study used wider spectrum of tyre pressures between
1,5-12 bar and over specified value changes in the pressure the Cr provided an orderly
0,001 decrease over every 1,5 bar increase of pressure which provided a curvilinear
graph. In that study Cr decreased gradually, by 62% between the smallest and the
highest tyre pressure values which is not true to present study where the this change
was 5,5% on asphalt, ~11% on fine gravel and ~8% on coarse gravel(5). Kyle and van
Valkenburg found the same relationship between Cr and tyre pressure like Grappe et. al.
They reported decreased Cr values as the tyre pressures increased. They used four
different tyre types (5). Ménard measured Cr at laboratory circumstances and found that
the relationship between tyre pressure and Cr depends on the features of a certain tyre
type (12). In the present study the front and rear tyre were not identical which may
caused differences in front and rear Cr values. Bertucci et. al. investigated rolling
resistance on three different surface and two tyre pressures. The two used pressure
were 2 and 4 bar where the difference was 2 bar like in the present study between the
lowest and the peak pressure. He didn't find any effect of tyre pressure on Cr either
rolling resistance as well like in the present study. Bertucci published measured Cr values
from former investigations as seen on table 6. These studies used two-wheeled normal
weight bicycles between 8-14 kg. On the other hand he found the same result like the
present study on the effect of surfaces on Cr.. He published that the contribution of
rolling resistance is getting higher as the rider use rougher surface. The rolling resistance
was increased on rougher surfaces and the proportion of it in total resistance was
changed to 21% on road, 35% on hard sand and 65 % on grass (1).
The results also indicated that the effect of tyre pressure on the TPO were not
curvilinear on any surface like in former studies but shows linearity on fine gravel. As
figure 2. shows the mean TPO values were irregularly changed into positive or negative
directions on asphalt and coarse gravel. On asphalt as the tyre pressure increased the
TPO increased until 3 bar but decreased at 3,5 bar and increased again at 4 bar and
finally decreased at 4,5 bar. But it should be mention that the decrease was barely 0,7 W
at 3 bar and 0,24 W at 4 bar. If it were excluded or consider as a measurement error
because of this small difference the data gradually decrease as tyre pressure increase
and shows linearity. In this case theoretically the asphalt data shows decrease over the
increase of tyre pressure which is the same result of the former studies even though it's
not curvilinear like in the study of Grappe et. al. which will be elaborated below. On
coarse gravel the TPO increase gradually as the tyre pressure increase until 3,5 bar
decrease by 8,1 W but increase again by 7,5 W. The difference of TPO at 3,5 bar and 4,5
barely 0,7 W. If the same theory was applied to these values as in the case of asphalt
and exclude the outlier and consider as measurement error, the relatively small
difference between 3,5 and 4,5 bar on the coarse gravel surface theoretically shows the
linearity as on the asphalt, but the values increasing as the tyre pressure increase which
contradict with former studies. The fine gravel shows the same linearly increasing

10. tendency. These results suggest that using the QuadRad on rougher surface the lower
tyre pressure induce lower power consumption. Grappe et. al. simulated the mean
power output to overcome rolling resistance and aerodynamic drag over the
aforementioned five different tyre pressures at a constant velocity. They found
curvilinear relationships between the tyre pressure and the power output overcome
rolling resistance and in parallel the power output overcome the aerodynamic drag
increased and related opposite but the chosen TPO was a constant 400 W at every tyre
inflation level. The power output to overcome rolling resistance decreased over
increased tyre pressure. After a comparison of the results of this simulation, the
statement of Faria et. al. and the present study, a contradiction emerged in case of the
rougher surfaces(5)(4).
Figure 3. Cr at different tyre pressures on different surfaces
Faria et. al. stated rolling resistance can influence TPO mostly in low velocities. The more
increased rolling resistance generates more increased TPO as well(4). Considering this
statement, in the present study in comparison of mean Cr values in table 1. and mean
TPO in table 2. at the same tyre pressures, the results have to suggest if mean Cr was
increase the mean TPO has to increase as well. In the present study this statement only
true to the asphalt data and the tyre pressure which provided the highest Cr value,
which is 3 bar, provided the highest TPO value. But this statement is not true to the
lowest values because 3,5 bar provided the lowest Cr while 4,5 bar the lowest TPO. On
the rougher surfaces some TPO values increased as Cr decreased and happened inversely
as well while in some case the directions of changes were the same without any
regularity.

11. Author Cr value
Pugh (1974) 0,0081
Kyle and Edelman
(1975)
0,0019±0,0039
Di Prampero et. al.
(1979)
0,0046
Davies (1980) 0,001
Gross et. al. (1983) 0,0030±0,0045
Kyle and Burke
(1984)
0,0016±0,0035
Kyle and van
Valkenburg (1985)
0,0017±0,0043
Menard (1992) 0,0028±0,0058
Capelli et. al. (1993) 0,0031
Grappe et. al. (1997) 0,003
Bertucci (2013) 0,010±0,0038
Present study (2015) Mean 0,017
Table 6. Measured Cr values from former studies
Comparing the Cr result of present study with the former studies on table 6. the values
were much higher in the case of QuadRad, that indicates the effect of transported
weight on Cr. The subjects of these studies were two-wheeled bicycles with the weight
between 8-14 kg which means their transported weight with the driver of QuadRad in
the present study would be 80-86 kg. The transported weight of the Quadrad was 150 kg
which is close to double. Zamparo et. al. tested a 28 kg four-wheeled recumbent bicycle
with 104 kg mean transported weight at 6 bar constant tyre pressure and measured
0,0084 mean Cr value on concrete while the Quadrad had 0,01357 at the closest 4,5 bar
pressure which is 160% of the result of recumbent bicycle. This suggests that nearly 50%
higher transported weight and the different structure of the four-wheeled bicycle can
resulted in 60% increase of Cr. The author hypothesise that over a certain transported
weight which hasn't investigated so far, but it is between 80-150 kg, the role of the
weight on measured results gets more important factor of influencing than assumes
before. Therefore these new results overwrite the results of former studies. The
relatively small changes of TPO in different tyre pressures on each surface possibly
means that the 150 kg transported weight had more influence on TPO than rolling
resistance, aerodynamic drag, mechanical- or hysteretic-loss and the required TPO to
drive a heavy-weight bicycle is close to identical at any tyre pressure and surface.

12. Comparing with the former study methods that methods used wider spectrum of tyre
pressures with a difference by 8-10 bar while this study operated within the range of 2
bar. The studies of four-wheeled bicycles recently not in focus of the main stream of
investigations because of their limited numbers in the markets. In the future a new
method for investigation of QuadRad should be develop and validate. For more reliable
results of subsequent studies identical tyres should be use in all of the wheels, as
Bertucci et. al., Macdermid et. al. and Ménard et. al. pointed out the importance of the
tyre surface on rolling resistance and on riding performance (1)(11)(12).
Conclusion
The results obtained in this investigation suggest that as the former studies stated the in
the case of a four-wheeled electric bicycle the tyre pressure did not show effect on Cr
and on TPO but the road surface had an effect on these values like in studies on two-
wheeled bicycles. However the results of Cr and TPO in comparison with former studies
results weren't match. The reason of this different results may be the almost doubled
transported weight, the different structure of the bicycle, the four wheels and the
effects of different tyres.
In regard of the high value of rolling resistance and transported weight comparing with
the ordinary bicycles, for the future a change in the structure of the bicycle should be
recommended for the designer to reduce these effects. The cross-linked tubular frame
made up by thick metal tubes, makes the structure heavyweight and its strenght is
gratuitous and unnecessary for the purpose of using. The suspension system is
complicated, a reduced version in size of an ordinary car's system which makes it heavy
and demands high number of parts. The solution would be a more conventional frame
about one strenght metal tube and a centrally suspended undercarriage which built
under mopeds. As high tyre pressure decreases the deformation of the tyre which
means lower hysteretic-loss, the designer should use slender tyres which requires higher
inflation pressure on larger diameter rims than 26”, and should think about the proper
thread type which appropriate for the purpose of using and users demand.
Acknowledgement
I wish to thank the help of Daniel Meyer and Gideon Kloss for their assistance. The
Technical University Munich Faculty of Ergonomics and the Faculty of Automotive
Technology to support during this investigation.

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