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 rollingresistance (Cr) and total power output (TPO) at five different tyre pressure levels and on three differentroad surfaces. Cr was estimated using riding velocity and power output and total power output wascombined power output of the motor and the driver. The author assumed that the effect of tyreinflation level has an effect on Cr and on TPO but the analysis of the measured data didn't showsignificant difference while there was significant difference between the road surfaces. In the presentstudy the mean change in Cr was 5,5% on asphalt, ~11% on fine gravel and ~8% on coarse gravel whileformer 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 formerstudies where the relationship of Cr and TPO with the tyre pressure was found to be curvilinear becausethe present results were closer to linear. The author hypothesises that role of the 150 kg transportedweight, which is way higher than in other studies, and the unique structure affects the data more thanassumed before.

Introduction

During cycling the velocity and power output of the cyclist depends on the resistanceswhich deter the movement. A former study determined that approximately 90 % of thetotal 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-bikingor when leaving the asphalt road the other resistances have more influence. Inmountain-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 andaerodynamic drag, lower speed means lower drag. In off-road circumstances the rollingresistance increases because the influence of the nature of the terrain and theproperties of the tyre have an effect as well. The rolling resistance defined as theresistance against the wheel motion caused by the contact of the wheel of the bike andthe surface of the terrain. The rolling resistance is considered independent from speedbut the results of Faria et al. showed that its contribution to the total resistanceincreases when the speed decreases (4). Bertucci et al. calculated the rolling resistance inmountain-bike field as well as road conditions and determined that the proportion was21 ± 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 onthe ratio of the rolling resistance. These values are different from the affore mentioned

90-10 % ratio and it is shown that the rolling resistance is two to three times lower onroad than in other terrains(1). The rolling resistance (Rr) can be calculated as themultiplication of the rolling coefficient (Cr) and the vertical force (Fv) which consists ofthe 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 caninfluence the performance in road cycling. In detail they showed that a 0.02 % decreaseof the Cr cause detectable positive changes in cycling performance (9). As mentioned before, the main factors of the rolling resistance are the terrain and thetyre. The resistance is generated at the point where the surface and the total area of thetyre 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 forceconsists of the mass of the bike and the rider while the value of the rolling coefficientdepends on tyre and wheel properties like wheel diameter, type, thread type, size andinflation pressure of the tyre (11). Generally larger contact area induce greater resistance.Therefore mountain-bike riders have to face greater rolling resistance than road bicycleriders, because the diameter of the rim is smaller, the wider tyre size has larger contactarea 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 aswell. Bertucci et al. compared a smooth and a knobby mountain-bike tyre in three fieldsurfaces (road, grass, sand) and found that the smooth tyre has 21+/- 15 % less rollingresistance than the knobby tyre, which means that rugged tyre surface cause higherresistance, but in certain surfaces it ensures better grip (1). Grappe et al. investigatedamong other the effect of inflation pressure on the rolling coefficient. They used fivedifferent tyre pressure between 150-1200 kPa and found that Cr decreased by 62 %between the extremes which ensured the assumption that the higher the inflationpressure the lower the resistance (5). A conventional mountain bike tyre which was usedon the subjected four-wheeled bike in the present study has a recommended inflationpressure 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 tyrepressure decreases the deformation of the tyre which means lower hysteretic-loss, butdecreases the gripping ability and increases transfer of vibrations from the surface whichcan be even more inconvenient in higher velocities (7). Wilson et al. published aninvestigation 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.

But experiences showed that it increases the rolling coefficient and therefore theresistance as well (15). According to the rules of physics more resistance requires moreenergy output from the cyclist and presumed that the bicycle is equipped with anelectric engine, from there as well. Recently electric bicycles are getting more popularamong customers and after the first pioneers many conventional bicycle companiesreleased their electric bicycles to the market. Whereas for the conventional bicycles therolling resistance affects the maximum speed achievable with a certain power forelectric bicycles the main resistances affect the range as well. An important issue forelectric bicycles is how to expand their range and how to estimate the residual rangewhich are the affecting factors. At first a higher capacity battery could be use, but biggerbattery has higher weight which again shortens the range. Also a low powerconsumption motor could be use. Usually, the lower power output motors are smaller insize and weight which is good considering the transported weight, but the performancemay not be enough to move the bicycle properly and in consequence increase thepower consumption. The range issue and its affects are mainly in focus of the studieswith electric bicycles like in case of the TUM QuadRad. Also, limited number of studies inthis 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 theinvestigation among others the velocity and both the energy output of the motor andthe driver were measured with a smart device. The rolling resistance was calculatedusing the measurement data. To the knowledge of the author four-wheeled bicycleswere rarely in the focus of former studies and there was no other investigation withelectric four-wheeled bicycle since the recent investigations in Technical UniversityMunich. In 2000. Zamparo et al. made a study about a four-wheeled recumbent bicycleand found that the rolling coefficient is averagely 60% higher than in a case of anordinary road bike. The best performance times on 1, 5, 10 km distances were 8% longerwith the four wheeled bike than the subjects performance on a road bike on the sametracks. The posture of the body of the driver was different and the bike was 28 kg whilethe QuadRad weights 78 kg, which means that the recumbent bike may have lowerrolling 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 witha slightly different prototype design using the same evaluation methods and test tracksunder similar conditions. Therefore, the aim of the present study is to get new results forthe rolling resistance coefficient and the total power output with a modulated bike inrelation with different tyre inflations with the intention of a subsequent comparisonwith the results of the former studies (8). The author hypothesises that the tests atdifferent tyre levels will show measurable and significant effect on the rolling resistancecoefficient and on the total power consumption. Additionally, different road surfaces willshow effect on these values as well.

MethodSubject

One male cyclist participated in the study. The age, weight and height of the personwere 33 years, 72 kg and 176 cm respectively. The subject was the author of the presentstudy.

Material

A QUADRAD Project four-wheeled electric bike powered by a Continental prototypeelectric motor and equipped with on board display and control system was used in thestudy. The total weight of the bike including all of the devices is 78 kg. Therefore thetransported mass with the driver is 150 kg. A Wiko Birdy Android 4.4.2 mobile phonewith an application called QUADRAD HMI recorded the raw data via bluetoothconnection with the on board system of the bike. The measured values among otherswere velocity, energy output of the electric motor and power output of the driver. AGarmin Edge 200 GPS device recorded the data of the location and the length of the testand a Garmin Express software exported data into a Microsoft Excel file. The tyre typeson the rear 32 spokes classic MTB wheels were two Schwalbe Racing Ralph MTB racingtyre (size:26x2.1; recommended tyre inflation 2-4 bar; 30-55 psi) and on the frontwheels 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 handpump 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 finegravel at five different velocities 5, 10, 15, 20, 25 km/h. The distance on each surfaceswas 650 m. The investigation was performed with five different tyre inflation pressureswhich 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 (3bar), 4) ideal pressure +16 psi (1 bar)=66 psi (4,5 bar), 5) ideal pressure – 16 psi (1bar)=34 psi (2,5 bar). The ideal pressure was chosen considering the maximal andminimal recommended pressures of the tyres. The test on each surface took place onthe same track with determined start and end points. These test tracks were used in aformer tests with a similar prototype bike and because of an intention of a comparativestudy between the two bikes, the subject used the same test tracks. The driver drove thebicycle 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 650m to isolate every measured part. The total tested distance was 292,5 km.

Statistics

The rolling resistance was calculated with the transformed equations using themeasured power and velocity data. The rolling resistance can be calculated by equation1. 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

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 rollingresistance and Vc is the velocity. This equation is transformed into:

Pext=0.5 ρairACdVc3+CrMgVc . 5.

which applied as a MatLab formula gave the figures of rolling resistance coefficient (C r).The raw data were cleaned of not used data and measurement errors. Subsequentlywith a Microsoft Excel template designed for this dataset, the mean velocities and totalpower 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 abovementioned formula. The formula was embedded into a Matlab script which analysed itwith a curve fitting algorithm. The correlation coefficients were determined for thelinear relationship between the tyre pressure and Cr, the tyre pressure and total poweroutput and between the surface, the tyre pressure and the Cr. Because of the numbers avariables group factorial analysis of variances (ANOVA) and post-hoc Bonferroni testevaluated the main variables. To use the ANOVA six assumptions have to accomplish. Atfirst the dependent variable should be measured at the interval or ratio level. Secondlythe independent variable has to consist of two or three more category and at third it'snot possible to be a relationship between the independent groups of observation. If thedata meets the first three assumptions, after the next three assumptions analyze by thesoftware. Assumption four states the outliers should be exclude while assumption fivedetermine whether the dependent variable is normal distributed on every independentvariable groups. Assumption six states the need of homogeneity of variances. Statisticalsignificance were set to P≤0.05. These statistics were performed with IBM SPSSsoftware.

ResultsThe 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 C r was between0,01324 and 0,01401 on asphalt, 0,01591 and 0,01722 on fine gravel and 0,01842 and0,02007 on coarse gravel. In the present study. The Cr increased from the lowest to the

peak value by 5,5% on asphalt, ~11% on fine gravel and ~8% on coarse gravel. On theasphalt surface the lowest value measured at 3,5 bar and the highest value measured at3 bar tyre pressure. At the other three tyre pressures the difference was ~2,5 % between0,01357 and 0,01393. On fine gravel surface the lowest value was at 3 bar tyre pressureand the highest measured at 3,5 bar and the same measured on the coarse gravel. Atthe other tyre pressures difference was 3,5% on fine gravel between 0,01601 and0,01659 and 5,5%, between 0,01856 and 0,01961 on coarse gravel. The statistical testindicated that there is no significant relationship between the different tyre pressuresand the changes in Cr at any kind of surface. On the other hand the tests indicated thatthere is significant changes in Cr on different surfaces. The average change of Cr on eachsurface 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 C r valuesare getting higher. Every Cr value at a certain tyre pressure is higher from smoother torougher surface. This figure assured the result of the statistical test which indicated thatthere 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 andsurfaces presented in table 2. and table 3. and 4. and 5. shows the mean TPO on certainsurfaces at different tyre pressures and velocities all coloured with green the lowest andwith red the peak values.

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. Thepercentage difference between the lowest and the peak value is ~4%. The lowest valuemeasured at 4,5 bar the peak value at 3 bar. Between the other tyre pressures thedifference was ~2%. Table 3. shows that on different velocities the four out of five peakTPO measured at 3 bar and one at 2,5 bar and three of the lowest values measured on4,5 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 tyrepressures the difference was less than 1%. Table 4. shows that on different velocities thetwo out of five peak TPO measured at 3,5 bar at the lowest 5 and 10 km/h velocities. At15 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 at2,5 bar. In the case of the lowest values at 5 km/h the measured lowest value was at 4bar, 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 wasat 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 191,254W (table 2.). The percentage difference between the lowest and the peak value was

~4%. The lowest value measured at 4 bar the peak value at 3,5 bar at the two extremesof the pressure line. Between the other tyre pressures the difference was ~2%. Actuallycomparing the mean TPO in table 2. of asphalt and fine gravel they show almost thesame values. Table 4. shows that on different velocities the peak TPO at 5 km/h was at4,5 bar at 10 km/h and 15 km/h the peak value was at 3,5 bar, at 20 km/h was again at4,5 bar and at 25 km/h it was at 3 bar. In the case of the lowest values at 5 km/h and 10km/h the measured lowest value was at 4 bar, at 15 km/h was at 4,5 bar, at 20 km/h itwas 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 tyrepressures on the total power output on each surface and no influence was experiencedon daily basis comparison on each surface as well. Figure 2. shows the mean TPO levelson the surfaces at different tyre pressures. The average mean TPO change on eachsurface is 4% in asphalt, 3,5% in fine gravel, and 4% in coarse gravel. Average TPOchange between asphalt and fine gravel is ~10,5%±3%, between asphalt and coarsegravel is ~20%±2% and between fine gravel and coarse gravel is ~9,5%±2% comparingthem in all of the tyre pressures.

Figure 2. Mean TPO on different surfaces at different tyre pressures

Discussion

The results in the present study indicated the effect of tyre pressure on C r is notcurvilinear as former studies stated. As figure 3. shows the average C r values on asphaltwere start and end on higher degrees and the lowest value provided by the middlemeasured tyre pressure level, at 3,5 bar. The other two surfaces show the oppositeprocess. The tyre pressure extreme rates were smaller and the peak value reached at themiddle 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 curvilinearrelationship between Cr and the tyre pressure levels. Cr was inversely and hyperbolicallyrelated to the tyre pressure. That study used wider spectrum of tyre pressures between1,5-12 bar and over specified value changes in the pressure the Cr provided an orderly0,001 decrease over every 1,5 bar increase of pressure which provided a curvilineargraph. In that study Cr decreased gradually, by 62% between the smallest and thehighest tyre pressure values which is not true to present study where the this changewas 5,5% on asphalt, ~11% on fine gravel and ~8% on coarse gravel (5). Kyle and vanValkenburg 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 fourdifferent tyre types (5). Ménard measured Cr at laboratory circumstances and found thatthe relationship between tyre pressure and Cr depends on the features of a certain tyretype (12). In the present study the front and rear tyre were not identical which maycaused differences in front and rear Cr values. Bertucci et. al. investigated rollingresistance on three different surface and two tyre pressures. The two used pressurewere 2 and 4 bar where the difference was 2 bar like in the present study between thelowest and the peak pressure. He didn't find any effect of tyre pressure on C r eitherrolling resistance as well like in the present study. Bertucci published measured C r valuesfrom former investigations as seen on table 6. These studies used two-wheeled normalweight bicycles between 8-14 kg. On the other hand he found the same result like thepresent study on the effect of surfaces on Cr.. He published that the contribution ofrolling resistance is getting higher as the rider use rougher surface. The rolling resistancewas increased on rougher surfaces and the proportion of it in total resistance waschanged 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 notcurvilinear on any surface like in former studies but shows linearity on fine gravel. Asfigure 2. shows the mean TPO values were irregularly changed into positive or negativedirections on asphalt and coarse gravel. On asphalt as the tyre pressure increased theTPO increased until 3 bar but decreased at 3,5 bar and increased again at 4 bar andfinally decreased at 4,5 bar. But it should be mention that the decrease was barely 0,7 Wat 3 bar and 0,24 W at 4 bar. If it were excluded or consider as a measurement errorbecause of this small difference the data gradually decrease as tyre pressure increaseand shows linearity. In this case theoretically the asphalt data shows decrease over theincrease of tyre pressure which is the same result of the former studies even though it'snot curvilinear like in the study of Grappe et. al. which will be elaborated below. Oncoarse gravel the TPO increase gradually as the tyre pressure increase until 3,5 bardecrease by 8,1 W but increase again by 7,5 W. The difference of TPO at 3,5 bar and 4,5barely 0,7 W. If the same theory was applied to these values as in the case of asphaltand exclude the outlier and consider as measurement error, the relatively smalldifference between 3,5 and 4,5 bar on the coarse gravel surface theoretically shows thelinearity as on the asphalt, but the values increasing as the tyre pressure increase whichcontradict with former studies. The fine gravel shows the same linearly increasing

tendency. These results suggest that using the QuadRad on rougher surface the lowertyre pressure induce lower power consumption. Grappe et. al. simulated the meanpower output to overcome rolling resistance and aerodynamic drag over theaforementioned five different tyre pressures at a constant velocity. They foundcurvilinear relationships between the tyre pressure and the power output overcomerolling resistance and in parallel the power output overcome the aerodynamic dragincreased and related opposite but the chosen TPO was a constant 400 W at every tyreinflation level. The power output to overcome rolling resistance decreased overincreased tyre pressure. After a comparison of the results of this simulation, thestatement of Faria et. al. and the present study, a contradiction emerged in case of therougher 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 moreincreased rolling resistance generates more increased TPO as well(4). Considering thisstatement, in the present study in comparison of mean Cr values in table 1. and meanTPO in table 2. at the same tyre pressures, the results have to suggest if mean C r wasincrease the mean TPO has to increase as well. In the present study this statement onlytrue 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 thelowest values because 3,5 bar provided the lowest Cr while 4,5 bar the lowest TPO. Onthe rougher surfaces some TPO values increased as Cr decreased and happened inverselyas well while in some case the directions of changes were the same without anyregularity.

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 vanValkenburg (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 valueswere much higher in the case of QuadRad, that indicates the effect of transportedweight on Cr. The subjects of these studies were two-wheeled bicycles with the weightbetween 8-14 kg which means their transported weight with the driver of QuadRad inthe present study would be 80-86 kg. The transported weight of the Quadrad was 150 kgwhich is close to double. Zamparo et. al. tested a 28 kg four-wheeled recumbent bicyclewith 104 kg mean transported weight at 6 bar constant tyre pressure and measured0,0084 mean Cr value on concrete while the Quadrad had 0,01357 at the closest 4,5 barpressure 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 canresulted in 60% increase of Cr. The author hypothesise that over a certain transportedweight which hasn't investigated so far, but it is between 80-150 kg, the role of theweight on measured results gets more important factor of influencing than assumesbefore. Therefore these new results overwrite the results of former studies. Therelatively small changes of TPO in different tyre pressures on each surface possiblymeans that the 150 kg transported weight had more influence on TPO than rollingresistance, aerodynamic drag, mechanical- or hysteretic-loss and the required TPO todrive a heavy-weight bicycle is close to identical at any tyre pressure and surface.

Comparing with the former study methods that methods used wider spectrum of tyrepressures with a difference by 8-10 bar while this study operated within the range of 2bar. The studies of four-wheeled bicycles recently not in focus of the main stream ofinvestigations because of their limited numbers in the markets. In the future a newmethod for investigation of QuadRad should be develop and validate. For more reliableresults of subsequent studies identical tyres should be use in all of the wheels, asBertucci et. al., Macdermid et. al. and Ménard et. al. pointed out the importance of thetyre 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 inthe case of a four-wheeled electric bicycle the tyre pressure did not show effect on C r

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 studiesresults weren't match. The reason of this different results may be the almost doubledtransported weight, the different structure of the bicycle, the four wheels and theeffects of different tyres.

In regard of the high value of rolling resistance and transported weight comparing withthe ordinary bicycles, for the future a change in the structure of the bicycle should berecommended for the designer to reduce these effects. The cross-linked tubular framemade up by thick metal tubes, makes the structure heavyweight and its strenght isgratuitous and unnecessary for the purpose of using. The suspension system iscomplicated, a reduced version in size of an ordinary car's system which makes it heavyand demands high number of parts. The solution would be a more conventional frameabout one strenght metal tube and a centrally suspended undercarriage which builtunder mopeds. As high tyre pressure decreases the deformation of the tyre whichmeans lower hysteretic-loss, the designer should use slender tyres which requires higherinflation pressure on larger diameter rims than 26”, and should think about the properthread type which appropriate for the purpose of using and users demand.

AcknowledgementI wish to thank the help of Daniel Meyer and Gideon Kloss for their assistance. TheTechnical University Munich Faculty of Ergonomics and the Faculty of AutomotiveTechnology to support during this investigation.

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