Graduate Thesis Or Dissertation
 

Kinetic and vibration analysis of off-road bicycle suspension systems

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/sx61dq277

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  • The aim of the present project was to quantify and compare differences in impact performance and damping effectiveness among various off-road bicycle suspension systems. Two experiments were conducted to compare suspensions. Fork impact performance was tested by measuring peak antero-posterior braking forces and impulses during impact with bumps of 6- and 10-cm height for five mountain bike suspension systems. These results were compared to a rigid fork condition. Comparisons among suspension systems showed small but significant differences in performance. While only marginal differences in peak force were found for the suspension conditions, more substantial differences in braking impulse were observed. Air-Oil design forks had the lowest braking impulse for the range of speeds and impact characteristics of this experiment. In another setting, an analysis of acceleration signals over a range of frequencies on two surface conditions (gravel and trail) was conducted to assess the damping effectiveness of the five suspension systems. The mountain bike was equipped with accelerometers mounted at the axle and frame. A spectral analysis of the signal was performed for each signal to provide a measure of fork effectiveness. Results showed that accelerations ranged from -33 to +40 g at the axle and from -13 to +13 g at the frame, while spectral analyses of the acceleration signals revealed two distinct frequency regions from 0 to 100 Hz and from 300 to 400 Hz. The various suspension systems were all effective in attenuating vibration over the first region. Vibration amplitudes at the frame were considerably less than at the axle for the suspension conditions while similar axle-frame vibrations were observed with the rigid fork. Lower frequency vibration amplitudes were typically greater on the trail than on gravel. In the frequency region between 300-400 Hz, the signal was attenuated at the frame for all conditions including the rigid fork. The quantification and comparison process of the various suspension forks using impulse provided an objective marker for performance, and allowed differentiation between various suspension conditions. Moreover, the effectiveness analysis through the use of accelerometers provided insight into the range of frequencies dampened by a suspension. The lower frequency range dampening suggested that effectiveness of a suspension fork can be quantified even though the experiment did not conclusively differentiate between the forks.
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