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Procedia Engineering 34 ( 2012 ) 479 – 484

1877-7058 © 2012 Published by Elsevier Ltd. doi: 10.1016/j.proeng.2012.04.082

9

th

Conference of the International Sports Engineering Association (ISEA)

Cycling comfort on different road surfaces

Christin Hölzel

a*

, Franz Höchtl

a

, Veit Senner

a

aTechnische Universitaet München, Department Sport Equipment and Material Parkring 35, 85748 Garching bei München

Accepted 02 March 2012

Abstract

The increased awareness for the environment and steadily higher costs for gasoline makes bicycles more and more attractive for short-distance traffic. Due to this the infrastructure of cycling pathways gets more important not only for safety reasons but also for the aspect of cycling (dis)comfort. Comfortable cycling requires smooth rolling at lowest possible energy input. To better understand this relationship, the objective of the study was to determine rolling resistance and the resulting accelerations due to external agitations for different surfaces.

Rolling resistance was quantified using a one degree of freedom pendulum (transversal rotation). By setting it at an initial angular displacement the measured decay of oscillations is a direct measure for the rolling resistance. To investigate the vibrations, an accelerometer was applied under the seat of a racing bicycle. The cyclist had to roll over a distance of 15 m at 3 different velocities with no pedaling. Four different surfaces were investigated. An effective value factor was defined for an overall description of the observed data.

The covered distance of the pendulum is directly related to the rolling resistance and varied from 22,1 m on concrete slabs to 10,2 m on cobblestones. Asphalt and self-binding gravel rank in between. This ranking however changes when analyzing the vibrations. Lowest effective value factors were measured on asphalt (0, 05) whereas concrete slabs (0, 17), self-binding gravel (0, 21) and cobblestones (0, 57) are far behind. Comfort decreases with higher velocities.

The results of this study allow suggestions about the best surface for cycling pathways thus making the systematic design of comfortable bicycle lanes easier. Designing bike lanes for comfort is an important issue to persuade more people to use the bike, especially the elderly population.

© 2012 Published by Elsevier Ltd.

Keywords: Cycling comfort; rolling resistance; cycling pathways

* Corresponding author. Tel.: +49 089 289 10351; fax: +49 089 289 15389. E-mail address: hoelzel@lfe.mw.tum.de.

Open access under CC BY-NC-ND license.

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1. Introduction

Due to higher gasoline costs and the increased awareness for the environmental protection cycling gets more attractive to people, which is a great development because more people using bicycles come along with less people using cars and therefore less traffic within the cities. In relation to this the infrastructure of pathways gets more important especially to enhance the cyclists comfort and safety. Cycling comfort requires smooth rolling with low energy inputs as well as a good ride quality as a synonym for few transmitted vibrations.

The rolling resistance (Rr) is one of the main sources of energy dissipations for bicycles. Cycling

comfort increases with lower rolling resistances because lower resistances stand for lower energy inputs. Several methods have been used to determine the Rr in former studies. Van der Plaas used the coast-down

method where a bicycle rolls down a constant grade slope [1]. The required distance to stop the bicycles movement is measured and the coefficient of rolling resistance (cr) can be directly calculated out of the

results by assuming that it is the predominant force during the test [1]. This method of examining the cr

requires smooth and absolutely even surfaces and is therefore not suitable for field tests. Three other methods, large diameter rotating drums, a tricycle configuration and a rotating oscillating weight, are known and were commented by Wang et al. [2] in 2004. He chose a method proposed from Hill in 1990 [3] first. Hill measured the Rr using an oscillating eccentric weight. Therefore two bicycle wheels are

rigidly fixed to an eccentric weight. Due to the weight the system is oscillating for and backward with a given initial angle. Based on the advantages of the system a similar appliance was used in this study.

Ride quality is an often used term to quantify the quality of a bicycle due to its frame geometry, especially its stiffness and damping. Published research has focused on material testing of road bicycle frames and on examining the vibration response of different bicycles without a rider [4]. There is less literature to find about transmitted road vibrations in cycling. Hastings et al. 2004 measured the effect of transmitted road vibration on the cycling performance [5]. They used a specially fabricated clamping system where the accelerometer was attached to and made standardized tests on a treadmill.

The aim of the current study was not to define the properties of different bicycle frames, or to investigate the effect of transmitted vibrations on the performance but to examine the transmitted vibrations on different road surfaces. Therefore a racing bicycle was equipped with a vertical accelerometer under the seat.

2. Methods

Rr was quantified using a one degree of freedom pendulum which was developed for this study (Figure

1 a). Therefore two bicycle racing wheels are rigidly connected by an axis.

Fig.1. (a) one degree pendulum; (b) racing bike with accelerometer and data acquisition hardware

V-velocity M-rotating

A

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An eccentric mass, consisting of a steel-plate, is welded on the axis. The sensor signals from the acceleration sensor, which is fixed at the end of the plate, are amplified by data acquisition hardware (National Instruments). The hardware, including analog digital conversion, was connected to a mini-pc confirmed at the steel-plate. A data logging software records the sensor signals with a sampling rate of 500Hz. The pendulum had a total weight of 27 kg which seemed to be a good compromise between transportability and inertia. The pressure of the wheels was set to 8, 5 bar. For all measurements the pendulum was rotated to an initial angle of 86, 2 degrees and released. It oscillated back and forth until it came to a complete stop. The whole procedure was performed for at least six times on one surface. For data mining the recorded voltage signals are transferred to acceleration over time signals. The acceleration curve is then classified by maxima und minima. By converting the acceleration data into orientation angles of the pendulum the covered distance is calculated. The last data mining step is examining the cr with the loss of energy. At the Beginning of the movement the pendulum has a potential

energy (Epot) which decreases due to the Rr until the movement stops.

ܧ݌݋ݐൌ ݉ כ ݃ כ ݄ ܧ݌݋ݐൌ ܧݎ݋݈݈ൌ ܿݎכ ݉ כ ݃ כ ݏ ܿݎ ൌ ܧ݌݋ݐ ݉ כ ݃ כ ݏ (1) (2) (3)

To examine riding quality a racing bike was prepared with an accelerometer and the data acquisition hardware from the pendulum (see Fig. 1). The sensor was attached under the seat whereas the hardware was fixed within the frame. Sampling rate was configured at 500 Hz and wheel pressure was set to 8, 5 bar. One rider (1, 90 m, 90 kg) rolled over the testing track of 15 m, without pedaling, while he kept his velocity (10 km/h, 15 km/h, 20km/h) constant. Therefore the surface had to be as even as possible to deny influences like acceleration or delay. At least three trials per velocity were measured. For data mining the voltage signals are transferred to acceleration signals by scaling and calibrating. Furthermore the analysis of the signals followed the VDI-norm 2057 to characterize the vibrations influence on the human body. Therefore the frequencies of the acceleration signals are valuated with a weighting curve ܹ which considers the influences of vertical oscillations on a sitting person. The important parameter to interpret the results is the effective value factor (awT) of the frequency valuated acceleration (aw(t)) which could be

calculated out of the frequency valuated signals. This parameter allows conclusions about the influence of the oscillations on the human being in a seating position (Table 1).

ܽ௪்ൌ ට ଵ ்׬ ܽ௪ ଶݐሺ݀ݐሻ ் ଴ (4)

Table 1. Effective values of the frequency valuated acceleration effective value awT of the frequency

valuated acceleration aw(t) description of the perception <0,01 not perceptible

just perceptible good perceptible strong perceptible <0,35 very strong perceptible

perception threshold 0,015

0,02 0,08 0,35

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Data collec (Fig. 2): asph considered by influences sur were the same testing day.

Fig.2. (a1) new a (d) self-binding g 3. Results The follow distances, the Regarding to asphalt, cobb Comparing th directly relate distances (Co highest cr of 0 Considerin and strong vib vibrations. As 0,21 and cobb Table 2. General surfaces asphalt (less concrete slab cobblestones asphalt (batt concrete slab self-binding

ction for the p halt, concrete y determining l rfaces were me e for the pendu

asphalt surface (a2 gravel

wing table give e rolling resis the mean valu blestones and hese results to t ed to the cr bec ompare Table 2 0,013225). ng the effective brations. Asph sphalt is follow blestones with t Results used) bs (less used) s tered) bs (battered) gravel pendulum as w slabs, cobble less used and b easured at two ulum and for th

) battered asphalt

es an overview stances and th ues the pendulu self-binding table 2 shows cause it could b 2: for example e values the res halt has the low wed by concre

the highest val

rolling resistance covered distance [m] 19,8 22,1 13,8 15,6 21 10,2

well as for the r stones and se battered surfac different place he racing bike.

surface; (b1) new

w about the res he effective v um covered the gravel. The d good agreeme be seen that sm e self-binding

sults are differ west effective v te slabs with a lue of 0,57. rolling resistan coefficient (cr) 0,0071804 0,0063459 0,0103079 0,0089477 0,0066998 0,013225

racing bike too lf-binding gra es of asphalt a es. The points w

Temperatures w concrete slabs (b2 sults of all me values with th e longest dista detailed distan

nt with the sta mall rolling res

gravel got the rent (Fig. 4). H value of 0,05 a an awTof 0,17, riding qualit nce ) effective val(awT) 0,05416666 0,16605882 0,57 0,10277777 0,18611111 0,21277777 ok place on fo avel. Influence and concrete sl where the mea s and wind kep

2) battered concre easurements, in he descriptions ance on concre nces could be atement that th sistances are e e lowest distan High effective v and therefore j , self-binding g ty lue subjectiv 7 good per 4 strong pe very stro 8 strong pe 1 strong pe 8 strong pe our different su es of weatheri labs. To captur asurements took pt constant due

ete slabs; (c) cobbl

ncluding the c s of the perc ete slabs, follow

e seen in Fig he covered dist equal to long c nce of 10,2m a values describe just good perc gravel with an ve perception rceptible erceptible ong perceptible erceptible erceptible erceptible urfaces ing are re local k place to one lestones; covered eption. wed by gure 3. ance is covered and the e many ceptible n awTof

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Fig. 3. Covered distances of the pendulum on different surfaces

Fig. 4. Effective values, investigated with the racing bike, on the different surfaces

Additionally to the less used surfaces, the parameters of battered asphalt and concrete slabs are analyzed. Concrete slabs show less degeneration (-5 %) than asphalt (-21%) regarding to the covered distance (Table 3). Considering the effective values the results are different again. Although the effective value of battered asphalt increases about 90% whereas the awT of concrete slabs increases about 12%,

asphalt shows lower absolute values than concrete slabs in any case (Table 3).

Table 3. Changes between the covered distance and the effective value of less used and battered asphalt and concrete pavement

surfaces covered distance [m] effective value awT

asphalt (less used) 19,8 0,054

change Ļ -21% Ļ 90%

asphalt (battered) 15,6 0,103

concrete slabs (less used) 22,1 0,166

change Ļ -5% Ļ 12%

concrete slabs (battered) 21 0,186

22.1 19.8 13.8 10.2 21 15.6 0 5 10 15 20 25

concreteslabs asphalt cobblestones selfͲbindinggravel

covered distance [m] Covereddistancesondifferentsurfaces lessusedsurfaces batteredsurfaces 0.05 0.17 0.21 0.57 0.10 0.19 0 0.1 0.2 0.3 0.4 0.5 0.6

asphalt concreteslabs selfͲbindinggravel cobblestones

effective

values

Comparisonoftheeffectivevalues

lessusedsurfaces batteredsurfaces

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The analysis of the effective values regarding different velocities showed a linear dependency of the

awT with increasing velocities. The awT for the velocities 10, 15 and 20 km/h were measured. The effective

values up to 30 km/h are calculated.

Fig. 5. Effective values of different road surfaces regarding different velocities 4. Discussion

Contemplating the comparison of concrete slabs and asphalt, shows greater effective values for concrete slabs whereas asphalt has a higher rolling resistance. Both of the other surfaces are far behind, regarding the awT as well as the cr, and therefore inadvisable for cycling pathways with high comfort.

Regarding the weathering concrete slabs perform much better than asphalt in both parameters. Nevertheless cycling on asphalt is much higher comfort, especially because of the fact, that the awT of less

used concrete slabs (0,17) is still much higher than the awT of battered asphalt (0,10). Finally that means

that despite its worse performance (+ 90%), asphalt is much better than concrete slabs overall.

Another interesting conclusion is that the effective values and therefore the riding quality are linear dependent from increasing velocities. For asphalt for example the awT increases from 0,035 (10km/h) over

0,05 (15km/h) to 0,09 (25km/h). Due to this perception is changing from good perceptible to strong perceptible while the comfort decreases. Finally it could be said that there are two good opportunities for cycling pathway surfaces. With Regards to the comfort asphalt is the most useful surface. Nevertheless concrete slabs are a good alternative due to their easier repairing properties. Summarizing, this study seems to be a good base to decide about cycling pathway design considering different demands.

References

[1] Van der Plaas R. Rolling Resistance of bicycle tires. Bike Tech 1983; 2:8-12.

[2] Wang E, Macedo V, Reid J. A method for quantifying rolling resistance of bycicle tires. In: Hubbard M, Mehta RD, Pallis JM, editors. The engineering of sport 5, Vol. 2. Sheffield: International Sports Engineering association; 2004, p. 132-138. [3] Hill B. Measurement of rolling resistance using an eccentrically weighted oscillating wheel. First international symposium on

surface chracteristics, State College, PA; 1990.

[4] Thibault J, Champoux Y. Rider influence on modal properties of bicycle frames. Canadian Acoustics/Acoustique Canadienne 2000; 28(3): 44-45.

[5] Hastings A Z, Blair K B, Culligan F K, Pober D M. Measuring the effect of transmitted road vibration on cycling performance. In: Hubbard M, Mehta RD, Pallis JM, editors. The engineering of sport 5, Vol. 2. Sheffield: International Sports Engineering association; 2004, p. 619-625. 0.000 0.200 0.400 0.600 0.800 1.000 1.200 9 14 19 24 29 effective value velocities[km/h] effectivevaluesofthedifferentsurfacesindependancyofthevelocity cobblestones selfͲbindinggravel concreteslabs (battered) concreteslabs(less used) asphalt(battered) asphalt(lessused)

References

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