Comparison Of Impact And Shock Attenuation Between Full- suspension And Front Suspension Bicycles J. P. Roy, B.Sc. D. G. E. Robertson, Ph.D. Biomechanics Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, CANADA

INTRODUCTION The rapid growth of the sport of off-road cycling has left the scientific community in the dark as to the differences in bicycle frame designs. Is the cycling population getting more riding performance from a full-suspended mountain bike as opposed to a bike equipped with only a front suspension, called a “hardtail”? Many off- road bicycle companies have developed fully suspended frames to increase impact attenuation but as yet these have not been evaluated by the scientific community.

Only one other study has been done in this field which analyzed front suspension impact attenuation 1. Few studies have dealt with shock attenuation in a sport setting and its effect on athletes 2,3. To compare full-suspension and hardtail bicycles, an off-road setting had to be created in a laboratory environment. The purpose of this study was to examine the differences in impact and shock attenuation between a full-suspension bicycle and a hardtail bicycle.

MATERIAL AND METHODS recorded ten trials by each of the subjects on each of the two bicycles ground reaction forces were collected using two Kistler force platforms data collection triggered by the contact of the front wheel on the first platform three seconds were sampled at 1000 Hz second plate had a 6 x 14 cm bump

two force platforms were spaced the same distance as the bicycle`s wheelbase so that reactive forces in the rear wheel could be measured when the front wheel impacted the bump forces normalized to the rider’s body weight by the BioProc data analysis software 4 signals smoothed by a low-pass critically- damped filter 5 with a cutoff of 150 Hz

“The Bump” 14 cm 6 cm

RESULTS Results in figures 1 and 2 show that the hardtail bicycle had a distinctly different pattern than the full-suspension bicycle. One major peak was evident for the vertical forces at the rear wheel as the hardtail bicycles passed over the bump. Force rose and fell rapidly to approximately twice the rider’s body weight. The full-suspension bike produced less vertical force than the hardtail bike. It also exhibited a more gradual vertical force decrease.

DISCUSSION AND CONCLUSION The results show that the full-suspension equipped bicycle attenuated vertical forces by 21% over those recorded for the hardtail bicycle. The vertical impulses created as the rear wheel passed over the bump were dampened and distributed over a longer period by the rear-suspension. This dampening effect reduces visual and vestibular organ disturbance allowing the athlete to see the trail better and to maintain better balance.

The rapid decrease of vertical force in the hardtail decreases wheel/ground contact. Traction is sacrificed and therefore performance and safety are also compromised. This means the rider will be able to brake and steer more efficiently with a rear-suspension equipped bicycle. Future work could use this method to analyze different variables such as altered frame designs and tire/wheel assemblies.

REFERENCES 1 Pritlove J. et al. (1997) Comparison of suspension and non- suspension front forks on mountain bikes, Proc. of NACOB III. 2 Derrick T.R. et al. (1998) Medicine and Science in Sports and Exercise. 30(1): Mahar A.T. et al. (1998) Medicine and Science in Sports and Exercise. 29(8): BioProc Data Processing System. URL: m m 5 Robertson, D.G.E et al. (1992) Response characteristics of different Butterworth low-pass filters. Proc. of NACOB II.