VERTICAL DISPLACEMENT AND VELOCITY CHANGE WHILE MOUNTAIN BIKING: COMPARING SUSPENSION FORKS TO A RIGID FRONT FORK

Abstract

464 Most mountain bikes sold offer the choice of suspension. Suspension is designed to improve rider performance by attenuating rough terrain. Various components are used to construct front suspension forks, but no published data exist on fork performance differences under identical riding conditions. The purpose of this study was to examine two front suspension forks marketed for cross country riding and compare their performance with each other and with a rigid fork. Four experienced mountain bike racers rode a rigid frame bike(RIG) and two suspension bikes with different front forks (FS1, FS2). Subjects performed five trials per bike, pedaling at the speed of their choice, then coasting 8.51m. A 2.74m bumps course was placed at the midpoint, consisting of four bumps 4-8.3cm in height. Sixty Hz video analysis revealed the velocity change of the bike before (PRE), during (ON), and after (POST) the bumps course, as well as the maximum vertical displacement of the front hub and the wrist of the rider over the bumps. An ANOVA was performed and tukey post-hoc calculated when indicated. Between PRE and ON, ON and POST, and PRE and POST, there was a significant decrease in velocity in all three bikes (p=.0001). There was no significant difference between bikes for maximum vertical displacement of the wrist or hub. The difference between the mean vertical displacement of the wrist and hub was: FS1=.028m, FS2=.011m, RIG=.036m. This may be clinically relevant, but not statistically significant due to low statistical power. A difference of.017m was noted between FS1 and FS2. The rigid fork bike showed the greatest vertical displacement difference between the hub and the wrist. This suggests that the front suspension forks may have contributed to force attenuation upon impact.