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ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS

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Rubber · Viscoelasticity · Kinematic · Suspension · Mountain Board

The present paper deals with the deve-lopment of a progressive rubber-sus-pension system as light weight const-ruction substituting a combination of a steel spring and rubber bushing system for sports equipment application. The new developed rubber suspension ele-ment uses the V-element geometry with respect to well-known non-linear mechanical behaviour of rubber and the expected non-linear relationship between required forces and the defor-mation of the suspension system. As example for application a mountain board in kiting sports was selected. The approach is based on the correlation between the kinematics of the athlete and the viscoelastic behaviour of rub-ber-suspension elements.

“Gummi” ein unverzichtbarer Werkstoff für Höchstleistun-gen in Sportanwendungen Gummi · Viskoelastizität · Kinematic · Dämpfer · “Mountain Board”

Diese Arbeit beschäftigt sich mit der Entwicklung eines progressiven Dämp-fungssystems als Leichtgewichtskonst-ruktion, welches ein Stahlfeder-Gummi-dämpfungssystem für z. B. Sportgerä-teanwendungen ersetzt. Das neu ent-wickelte Gummi-Dämpfungselement nutzt eine V-Elementgeometrie mit Be-rücksichtigung des bekannten nicht-li-nearen mechanischen Verhaltens von Gummi und dem zu erwartenden nicht-linearem Verhältnis zwischen geforder-ter Kraft und der Deformation des Dämpfungssystem. Als Beispiel für eine Anwendung wurde ein „Mountain Board“ im „Kite“-Sport ausgewählt. Der Ansatz basiert auf der Übereinstim-mung zwischen der Kinematic des Ath-leten und den viskoelastischen Verhal-tens des Gummi-Dämpfungselements.

Figures and Tables:By a kind approval of the authors

IntroductionPopular sports e.g. kiting, mountain-boarding, mountain-biking etc. based on extreme feeling are rapidly growth around the world. But these are very de-manding activities for the human body of the athlete. There always is an ele-ment (technical component) in the sport equipment, which is used for given acti-vity, connecting the ground and athlete; therefore this element has a maximum effect on the absorption of vibration caused by crossing over the road terrain or jumping impacts etc. Only one basic system is commonly used for the sport equipment, which are mountain board (MB) for kiting and mountain-boarding or bike for mountain-biking, whose func-tion is to absorb vibrations and shocks: a pneumatic rubber tire. The suspension is another component of the sport equip-ment that has a potential to absorb the vibrations caused by riding. Thus our aim of the work is focused on study of development of a full-rubber suspension system and its influence on athlete feeling and its motion kinematic by performing of extreme sport, which in our study exemplary is kiting and moun-tain-boarding.

Usually, this suspension system im-plemented in mountain board provides support to the ride and handling perfor-mance, implemented by using a combi-nation of steel springs with rubber shock elements (Fig. 1, a); the next system is based on annular bushings made from hard rubber and placed under the truck’s fixing bolt (Fig. 1, b). Both the common suspension systems, that are represen-ting different technical solutions, are based on viscoelastic behaviors, thereby they are able to follow the non-linear re-sponse of loading, and absorb the vibra-tions and shocks. From the mechanical point of view common suspension that is based on spring combined with rubber shock element (located outside of center of rotation) ensures easier transmission of applied torque on the board in compa-rison with the annular rubber bushing positioned in the center of rotation. However, the spring increases the weight

of the mountain board and the weight of sport equipment is a critical factor for each of athlete. On the other hand, be-cause of the location of the bushing ele-ment in the center of rotation, it is expo-sed to increased loading and fatigue con-ditions that is also a crucial factor. Thus, the newly developed system based on a combination of the full rubber-suspensi-on elements and the position outside of the center of rotation represents an ideal solution for the support of the ride and handling performance of the truck sys-tem. The rubber suspension element is carried out corresponding to the deve-lopment of the rubber V-element geo-metry shown schematically in Fig. 2. The V-geometry has been developed with re-spect to well-known non-linear mecha-nic rubber behaviour and expected non-linear relationship between forces requi-red for the deformation of suspension system by rider. The circle shape of V-geometry given by radius R1 and R2 (see. Fig. 2) ensure a defined non-linear beha-viour of the V-element stiffness about its complete deformation with respect to the rider‘s requirements.

Furthermore the study concentrates on the description of the correlation bet-ween the kinematics of the riding and the required mechanical behaviour of the implemented V-elements to provide better absorption of vibrations and shocks. The mechanism of the mountain

“Rubber” an indispensable Material for high Performance in Sports Application

AuthorsRadek Stoček, Zlín, Czech Republic, Petr Blažek, Jan Veselý, Slatiňany, Czech Republic, Hannes Michael, Daniel Schönfelder, Chemnitz, Germany Corresponding author: Dr.-Ing. Radek StočekCentre of polymer systemstřída Tomáše Bati 5678, 76001 Zlín, Czech Republic E-mail: [email protected]: +420 57 603 8010


21KGK · 1-2 2017www.kgk-rubberpoint.de

board’s kinematics is based on compres-sion of the V-element at a closed stage and on tension at the open stage (see. Fig. 2). The non-linear progressive res-ponse on deformation of the V-element is provided due to a special geometry re-presented by V-cut with depth xS12 and with a gap angle γ. The definition of non-linearity of the rubber based on different rubber compounds was analysed by me-ans of a real test of the V-element under laboratory conditions. The tension mode presents a more critical state of the loa-ded product because the V-cut opens in comparison with compression, where the V-cut closes. Thus, an important aim of this research was to validate the dura-bility of the V-elements by means of a fatigue and dynamic crack growth analy-sis under tension.

This paper also deals with the identifi-cation of subjective parameters of ride feeling with commonly used suspensi-ons in comparison with the newly deve-loped suspension system that is to be used for downhill and for power kiting rides.

The kinematic analysis of rider and mountain board Fig. 3 shows the kinematic model of the rider’s and the mountain board’s move-ments with the applied drag force co-ming from a kite. The calculation of kine-matics used in this paper is based on the kinematic model with the applied kite’s load, applied also to the kinematics of a downhill rider, because of the similar movement of riders and of the mountain board during different types of riding.

The kinematic model basically con-sists of determining the position of all bodies and parts in the analyzed system by knowing the positions of the fixed and the driven bodies. The fixed ele-ments in the system of the athlete and the mountain board are the wheels and the bottom parts of trucks. Thus, the fixed point and the origin of the coordi-nates are situated towards the center of rotation of the trucks denoted P1 in Fig. 3. For the simple feasibility of the kinema-tic analysis we assumed a constant posi-tion of the kite in the coordinate, and thus the model includes the second fixed point denoted P2 in Fig. 3. The driven parts of the mountain board “board with the upper part of trucks” are fixed to the feet, thus creating the connecting parts. The power and driving lines of the cano-py are bonded with kite bar, which is held by the athlete’s waist harness. Finally,

the complete system and model consist of 2 fixed points and 8 driven bodies or elements. The relative masses ∆G [%] of each driven body related to the mass of the complete body G = 100% and the ra-

dius of center of gravity of each driven body are listed in Table 1. The united center of gravity of the athlete is sche-matically shown in Fig. 3 and is labeled CoG.

Fig. 1: Conventionally used truck systems for supporting the ride and handling performance; a - parallel combination of the spring and shock element; b - hard rubber bushing placed under the fixing bolt of trucks.

1

Fig. 2: Schematic visualization of the V-rubber element’s geometry and its location on the MB.

2

Fig. 3: Kinematic model of athlete’s and MB’s motions with load applied by a kite.

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The force applied on the V-element FS is a function of the gravity force FG, tensi-on force FT in dependence on angle β as well as of the CoG position and is given by ( )

⋅+⋅⋅−⋅⋅=

2sincos1 CoGCoGTCoGG

FSS

xyFxFx

F ββ

(1)

MaterialsThe rubber compositions and their beha-vior were studied after the reception of the industrial rubber product [7]. The natural rubber (NR) used for the produc-tion of V-elements in this study was Standard Malaysia Rubber (SMR 10) filled with different loadings of silica (Ultrasil GR 7000, Evonik Degussa GmbH, BET surface area). The silane of the tye Bis-(triethoxysilylpropyl))tetrasulfane) was used as silanisation agent. N-isopropyl-N’-phenyl-p-phenylendiamine (IPPD), n-cyclohexyl-2-benzothiazole-sulfenamide

(CBS), kindly provided by Rhein Chemie, and both soluble sulfur (S) and zinc oxide (ZnO) were used as the vulcanization system. Four different pigments were used to distinguish and label rubber compounds or V-elements for future use.The compounds were prepared in three steps in an internal mixer (made by Hein-rich Schirm) with a 3.0 liter capacity. In the first step, rubber matrix and silica were mixed for 5 min at a temperature of 80°C. In the second step the silane was added for silanisation at 140°C and the total time of mixing in the internal mixer was determined to be 15 minutes. In the last step the remainder of the anti-aging additives and vulcanization system were added at 40°C on the two-roll mill.

Four different compounds were prepa-red due to the modified content of silica in the range 20-60 phr. The increasing silica content corresponds to the hardness of rubber and each rubber compound based on a different hardness, whereas the hardness was determined according to ISO 868, whereas the hardness was deter-mined according to ISO 868: Shore A 40 (Sh-40); Shore A 45 (Sh-45); Shore A 40 (Sh-40); Shore A 45 (Sh-45); Shore A 50 (Sh-50) and Shore A 60 (Sh-60).

Two different geometries were cured according to the rheometric properties analysed by using Moving Die Rheome-ter MDR 3000 Basic (Co. MonTech GmbH):a) plates with the dimensions of 100

mm x 200 mm x 15 mm (length-L0 x width-W x thickness-B) for cutting a different V-element geometry. Four varied geometries of V-elements were prepared and are listed in accordance with the schematic Fig. 3 in Table 2. The variation of geometry is based on the different radiuses R1 and R2. The V-elements were manufactured using a water jet cutter. The geometry of the V-element corresponds to the sche-matic visualization shown in Fig. 2.

b) monsanto pure-shear test specimens with dimensions of 15 mm x 120 mm x 1.5 mm (L0 x W x B) commonly used for the fatigue crack growth analysis (for a detailed shape of the test speci-men see [11]).

Experimental details

Determination of FS from the CoG positionA determination of the CoG position was performed through a real experimental simulation of the athlete’s movement under laboratory conditions with respect to the theory based on calculation of ap-plied load concentrated to the united center of gravity [3, 6]. The experimental analysis was based on the capture of the moved athlete’s body from its vertical position to an extremely low position. The digital picture of the athlete’s body was simultaneously captured during the entire movement, whereas the tension force FT applied by the body onto the bar and, thus onto the kite line, was determi-ned by a mechanical load cell. The estab-lishment of the analysis is visualized in Fig. 4. The positions of CoG were evalua-ted according to the x,y axes system with the center of axes being P1. The calculati-on of the CoG position was performed by the equations:

COG

ni

iii xGx∑

=

=

=∆⋅1

; COG

ni

iii yGy∑

=

=

=∆⋅1

. (2)

1 Relative mass and radius of the center of gravity.

Parts of the human body

Relative mass ΔG [%]

Radius of center of gravity [%]

Head 6.72 Ear canalTrunk 46.30 44Upper arm 2.65 47Forearm 1.82 42Wrist 0.70 MiddleThigh 12.21 44Leg 4.65 42Foot 1.46 44

2 The geometries of produced V-elements based on varied radiuses R1 and R2.

Labeling Length L0 [mm]

Width W [mm]

Thickness B [mm]

Radius R1 [mm]

Radius R2 [mm]

Distance xS12 [mm]

Distance YS12 [mm]

Angle γ [°]

R_35

32 60 15

35 45

37 10.5 16R_45 45 55R_67 67 75R_115 115 125

Fig. 4: Experimental analysis of CoG position with the detail on the measuring equipment.

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The relative mass ∆G listed in Table 1 was used for to calculate the gravity force FG. We determined the CoG position in de-pendence of the angle β whereby this angle marginally varied during the athlete’s movement (range ±2.5°), but becomes highly significant for a different position of the kite in the space. Two dif-ferent angles β relevant firstly to higher and secondly to average force of kite were taken into account. The higher force of kite is simulated by angle β and correlate with the position of kite at 9 o’clock, whereas the average force is simulated by angle β and correlate with the position of kite at 10 o’clock.

Compression test of V-ElementsThe compression tests of cured V-ele-ments were carried out using the materi-al testing equipment TIRA 27025 - 2,7 kN (TIRA GmbH) with a cross-head speed of 200 mm/min. The test was carried out according to the real loading kinematics of the mountain board for the V-ele-ments based on the material with mini-mal (Sh-40) and maximal (Sh-60) hard-ness, because extreme data can be ex-pected. Four V-elements were analysed for all dimensions listed in Table 2. Du-ring the experimental analysis a relation-ship between the deformation of the V-element defined by the angle α (turn of the board towards the truck) and the applied force will be characterized. The arrangement of the testing equipment and the proceedings of the analysis are shown in Fig. 5.

Fatigue crack growth analysisCharacterization of crack propagation in elastomers is based on a global energy balance in which the tearing energy was introduced by Rivlin & Thomas [9] as the energy required for the creation of a unit area of a new crack surface. Considering the special case of crack propagation in a pure shear specimen without crack de-flection, the tearing energy T can be estimated by

0LwT ⋅= , (3)

with w being the strain-energy-density, which is determined by a measurement of the tensile stress-strain curve of a un-notched test specimen, and L0 is the length of test specimen in the unstrai-ned state. Gent et al. [5] found the crack growth rate per cycle da/dn to be a func-tion of the tearing energy T, which is de-fined as

mTBdnda

⋅= , (4)

where a is the crack length, n is the num-ber of cycles, B and m are rubber crack growth parameters.

The fatigue material behavior was characterized by an S-N curve, also known as a Wöhler curve. A rubber mate-rial changes its S-N curve radically after the first application of a load and conti-nues to change its behavior thereafter, depending primarily on the magnitude and timing of the deformations. This phenomenon is referred to in many pub-lications as a cyclic or time dependent property, e.g. [1, 2, 4, 5].

The fatigue crack growth tests were performed with a tear analyzer (TA) (Coesfeld GmbH) and the following testing conditions were set: sinusoidal loading mode, frequency 1 Hz, loading amplitude 13%, 16% and 20% of the ini-tial length L0, controlled stress σmin = 0.01 MPa and the tests were performed in the laboratory atmosphere at 28°C. Two dou-ble notched and simultaneously one un-notched specimens were analyzed for

each of the loading amplitudes. The double notched test specimens were used for the fracture analysis and, simul-taneously, the fatigue behavior was ana-lyzed in the un-notched test specimen. The main details of the analyzed test specimen’s geometry and of this experi-ment are described in [10-12]. The ser-vice lifetime of V-elements was set at 140 hours.

Results and discussion

Determination of the CoG position and calculation of the theoretical value FsThe evaluated data of the CoG position evolved from the initial upright attitude of the athlete according to two different settings of the kite defined by angle β in current position are plotted in Fig. 6. The data describing the real position of the athlete’s movement when riding show a more or less similar curve.

The non-linear curve of the CoG posi-tion is the reason for the non-linear rela-tionship between FS and angle α, which is shown in Fig. 7. The FS data were evalu-

Fig. 5: Arrangement of testing equipment and loading of V-elements, with a – V-elements, b – arrangement of real V-elements’ compression loading, c – load cell.

5

Fig. 6: CoG position according to the two different angles β and with respect to the athlete´s moving.

6



ated based on the experimental measu-rement of CoG curves shown in the Fig. 6 by using equation 1, where the other parameters used for calculation were set as follow:

■ gravity force FG = 931,95 N in accordance to the weight of athlete, which was 95 kg;

■ tension force FT was established from the experimental measurement and the values varied for the both of curves defi-ned by angles β dependent on angle α in the range from 0 up to 800 N.The relationship between the theoretical value FS according to the angle α shows a difference in dependence on the varied CoG position curve evaluated for varied angles β. Thus the middle curve was eva-luated in this way (Fig. 7).

Influence of V-Element geometry and hardness on FsThe effect of the V-element geometry on FS is demonstrated in Fig. 8. The reducing of radiuses R1 and R2 has a decreasing effect on the relationship between FS and angles α independently of the rubber compound type. The variation of radius-es R1 and R2 does not influence the relati-onship between FS and angles α up to angle α = 8°. This can be understood since the deformation proceeds between the areas defined through the line seg-ments |S12P1| and |S12P2| (Fig. 2).

The hardness of the V-element based on different filler amount in rubber com-pound has a predominant effect on FS - angle α dependence in comparison with

the effect of different V-element geome-try. Fundamentally, as expected, it is found that the higher values of the forces FS, i.e. greater stiffness of the rubber, is based on the compound with an increa-sed content of filler.

The middle curve FS - angle α evalua-ted from the calculated curves (See Fig. 7) is inserted into Fig. 8 and compared with experimentally determined data. It was found that the theoretical curve ne-arly overlaps the experimental FS - angle α curves of rubber with the hardness Sh-40 over the complete range of varied ra-diuses R1 and R2. Thus, the expected non-linear behavior of the rubber V-element was confirmed, and the optimal rubber compound was defined with respect to the athlete’s motion. For practical use and the real test of the V-element we applied the material Sh-40 with the geo-metry R-115.

Fatigue crack growth analysisIn Fig. 9, the influence of a different structure of the rubber composition on the crack growth rate becomes appa-rent. We found fundamentally that the compound Sh-60 shows the lowest crack growth rate for the given tearing energy, whereas the crack growth rate is significantly lower in the compound Sh-40 up to a value of log T<-0.3N/mm in comparison with the data for com-pounds Sh-45 and Sh-50. In particular, it is found that the loading amplitude marginally induces a difference of the crack growth rate in compounds Sh-45, Sh-50 and Sh-60, whereas the tearing energy significantly increases with the increasing value of hardness. The influ-ence of the loading amplitude has the greatest significance in compound Sh-40, where the lowest crack growth rate was determined for the given amplitu-des. Therefore the material Sh-40 has the highest crack growth resistance for the given application.

Fig. 10 represents a fatigue life based on the S-N curve for the studied com-pounds at the maximal strain amplitude of 20%. It was verified that a plot of the fatigue dependence on the dynamic strain energy has a constant character for all analyzed compounds over the complete service lifetime. The rubber test specimen based on the compound Sh-60 shows a decrease in stress at the range up to 20,000 cycles, and continues constantly over this value. The reason for this phenomenon is the formation of a network formed by filler-filler interaction

Fig. 7: Calculation of the theoretical value FS according to the angle α with respect to the different position of the kite in the space.

7

Fig. 8: Influence of the V-element geometry on the force FS according to the different angles α and the relationship between experimental and theoretical values.

8



[8]. Obviously, the fatigue analysis has demonstrated the resistance of the com-pounds to fatigue over the entire service lifetime.

Real testing of the mountain board in dependence on the type of suspensionThe testing and interviews regarding different suspensions based on the commonly used combination of steel springs with rubber shock elements, annular rubber bushing elements and the newly developed V-elements based on the compound Sh-40 and the geome-try R-115 were also conducted to obtain statistically based subjective ratings. The observation of qualitative feeling requirements are based on the previous work of Subic et al. [13] and modified for the mountain board in Table 3. Five professional power kiting instructors, with a similar physique and a body weight of between 80-85 kg, were em-ployed to ride a set slalom on a downhill road and, secondly, using a power kite on a set slalom course that examined each suspension system’s ability to ab-sorb shocks and to undertake turns of a varying difficulty and to perform jumps. After performing 5 rides, the riders were interviewed as to the levels of each sub-jective parameter of the suspension presented in the tested mountain board (on a scale of 1–10, where 10 means the best), and whether these levels were, in their opinion, soft, optimal, or too tough. If assessed as optimal, the riders were asked to further estimate the mar-gin by which the subjective parameters varied from optimal levels. All riders used the same board model, wheels, trucks and the same type and size of binding. The tests of the power kite we-re performed using the kite type Aero 10 (Co. PEGAS), with the active power of 10 m2. The tests were undertaken at the average temperature of 24°C and at a wind velocity of 8 m.s-1. The evaluated average values of each subjective para-meter for all three test boards are dis-played in Table 4.

The riders stationed lowermost, clas-sified the mountain board equipped with the suspensions based on annular rub-ber bushing element in all of subjective parameters except maneuverability. The level of maneuverability was found to be identical with the level assigned to the V-element. The riders classified the maneuverability of the suspension sys-tem based on annular rubber bushing element as high leveled, because of the

subjective feeling of low toughness of the system and thus reduced forces re-quired for operating with mountain board. The riders finally classified the suspension system based on annular rubber bushing element to be unstable. Contrariwise, the mountain board equip-ped with the suspension system based on steel springs combined with rubber shock elements was classified to be very stable. However the most identical sub-jective feeling of all riders was to get ac-customed to operate the mountain board, whereas the main reason was the

feeling of non-natural response of moun-tain board in driving. The riders found the mountain board equipped with the suspension system based on the V-ele-ments to behave most naturally in the view of rider’s feeling by driving of mountain board. Finally, these results according to the subjective parameters given by five professional riders proved the highest positive score for the suspen-sion system based on rubber V-elements in comparison to commonly used sys-tems in both sport disciplines - downhill riding and power kite slalom.

Fig. 9: Power law behavior of the fatigue crack growth rate vs. tearing energy for rubber compounds based on a different hardness.

9

Fig. 10: S-N -curve estimated for all varied rubber compounds analysed over the service life time of 140 hours and for the loading amplitude of 20%.

10



ConclusionThis paper studied the commonly used mountain board suspension system used for down-hill riding and kiting. The description of the kinematic motion of athlete showed a non-linear relation-ship between the position of CoG and angle α (turn of board towards to truck) and, thus, the requirement on a non-li-near response of the suspension. We developed a new geometry of the sus-pension based on rubber-like material that has a non-linear stress-strain beha-vior. The rubber-like material was modi-fied with a different content of filler to establish a varied stiffness of the V-ele-ment, defined according to its hardness in the range from shore 40 to shore 60. Four modified geometries of the V-ele-ment were studied in experiments. We found that the modified geometry has only a marginal effect on the response of the V-element on the mountain board motion. We found that the theoretical athlete response curve nearly overlaps the FS - angle α curve of rubber Sh-40. Thus, a rubber compound and V-ele-ment geometry with respect to the re-quired non-linear behavior of the sus-pension system with respect to the athlete’s motion has been developed. We proved experimentally that the rub-ber based on compound Sh-40 has the

highest crack growth resistance for the given application, whereas none of the analyzed materials showed any changes during the fatigue test over the entire service life time. For the real test of the V-element we used the material Sh-40 with the geometry R-115. Finally we tested the suspension system in practi-ce – by using the mountain board in extremely varied conditions. The results according to the subjective parameters given by five professional riders proved the highest positive score for the sus-pension system based on rubber V-ele-ments in comparison with commonly used systems in both sport disciplines - downhill riding and power kite slalom. Thus, the real progressive rubber-sus-pension system of the mountain board with respect to the kinematic of the athlete has been developed and evalua-ted for the first time. In this study, a high potential of rubber material for high performance in extreme sports ap-plication has been shown.

AcknowledgementThis article was written with the supportof the Operational Programme ‘Researchand Development for Innovations’ cofun-ded by the European Regional Develop-ment Fund (ERDF) and the national bud-get of the Czech Republic, project: Centre

of Polymer Systems (reg. number: CZ.1.05/2.1.00/03.0111) and CPS - strengthening research capacity (reg. number: CZ.1.05/2.1.00/19.0409).

This work was supported by the Mi-nistry of Education, Youth and Sports of the Czech Republic – Program NPU I (LO1504).

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[4] Bauman, J.T.: Fatigue, Stress, and Strain of Rubber Components, A Guide for Design En-gineers. Carl Hanser Verlag, Munich (2008)

[5] Gent, A.N., Lindley, P.B., Thomas, A.G. Journal of Applied Polymer Science, (1964), 455.

[6] Hochmuth, G.: Biomechanik sportlicher Be-wegunge, Sportverlag Berlin (1982).

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[8] Payne, A. R., J. Appl. Polym. Sci.7, (1963), 873.[9] Rivlin, R.S., Thomas, A.G., Journal of Polymer

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3 Subjective parameter definitions.Subjective parameter DefinitionStability How stable the rider feels on the boardManoeuvrability How easily the board responds to rider inputsAccuracy Precision of the board movement in response to rider inputsTurn‘s stability Level of stability during turns

Feedback Amount of stress felt by the rider’s body including the effects of board shattering

Forgiveness Tolerance of the board to errors made by the riderLiveliness The level of stability at landing after performing a jump

4 Subjective correlation data, where S-R represents steel springs with rubber shock ele-ments, A-R is the annulus rubber bushing element and V-R is the V-rubber element.

Subjective parameterDownhill ride Power kite slalomS-R A-R V-R S-R A-R V-R

Stability 8.60 7.00 9.00 8.00 7.80 8.40Manoeuvrability 7.00 8.60 8.60 7.00 7.80 8.00Accuracy 8.00 4.60 8.20 8.00 5.60 8.20Turn’s grip 8.40 5.40 9.40 8.60 6.60 9.00Feedback 6.40 6.20 6.80 6.20 7.00 6.80Forgiveness 8.00 6.00 8.00 7.40 6.80 8.00Liveliness 9.20 4.20 9.40 8.80 4.40 9.60

Average value 7.94 6.00 8.49 7.71 6.57 8.29