Introduction: Equipment innovations in mountain biking have touched nearly all components of a cycle including the wheels where larger diameters are now commonly used. Systematic comparison of riding kinematics for different wheel dimensions has not been investigated. This study`s purpose was to compare 26 and 29 inch wheel vibration amplitudes at various frequencies on a standardized track with rigid and suspension fork conditions. Methods: A standardized indoor track of 10 m length was built using plywood and wooden strips of various heights (1 to 7 cm). This provided a repeatable surface similar in roughness to a natural surface trail. Fork and handlebar accelerations were measured at 1500 Hz using PCB 356A32 accelerometers and wireless transmission to a nearby computer. Two front wheels of 26 and 29 inch diameter were matched in most characteristics (rim, tubeless tire, pressure) but differed in mass by 100 g (7% greater for the 29 inch wheel). The same hardtail carbon frame (Niner Air 9 with 29 inch rear wheel) was used for all testing. Rigid (R) and suspension (S) front forks (White Brothers Rocksolid; Rockshox Reba, respectively) were tested with each wheel condition. A single rider performed 10 trials with speeds between 2 and 8 m/s for each wheel/fork condition. Each trial traversed the measurement track passively without lifting or pedaling. Fourier analysis was used to calculate amplitude coefficients for each trial within a frequency range of 0 to 100 Hz. Fork amplitudes were compared for the R and S condition. Comparisons of amplitudes for each wheel size at each frequency level were made using t-tests, for each suspension condition. Results: The largest fork amplitudes occurred between 7.5 and 12.5 Hz. The R condition produced amplitudes of 0.282 and 0.293 g (26- and 29-in wheel, respectively). In the S condition, amplitudes were significantly larger: 0.478 g for 26-in and 0.538 g for 29-in wheel. Wheel comparisons were significant for the S condition in the range of 20 to 40 Hz (p<.05). No significant comparison was found in the same range for the R condition. Fork amplitudes were consistently larger in the S condition for both wheels. Discussion: Fork amplitudes revealed small measurable differences between wheels in the range of 20 to 40 Hz in the S condition. However, this observation was not repeated in the R condition, even if the trend was similar with smaller amplitudes. Fork amplitude does not appear to differentiate well between these two wheel sizes, but can be a sensitive variable when comparing suspension conditions. Other tracks built to produce higher vibration frequencies may yield different conclusions.
© Copyright 2014 19th Annual Congress of the European College of Sport Science (ECSS), Amsterdam, 2. - 5. July 2014. Veröffentlicht von VU University Amsterdam. Alle Rechte vorbehalten.