An Off-Road Bicycle With Adjustable Suspension Kinematics

Abstract

The purpose of designing and constructing the adjustable dual suspension off-road bicycle presented was to provide a research tool for quantifying and optimizing off-road bicycle performance in three categories: energy efficiency, comfort, and handling. Key variables affecting performance in each category were identified and then the bicycle was designed and constructed so that one variable may be changed at a time. For both the front and rear suspensions, independent modular springs and dampers may be used, so that the travel limit, damper quantities, and spring, quantities can all be independently tested. On the rear suspension, the swingarm pivot point height may be moved along the seat tube from the bottom bracket to 22 cm above the bottom bracket. The swingarm was integrated into a four-bar linkage such that the effective spring and damping rates at any pivot point height were constant as the suspension compressed. For the front suspension a four-bar linkage was also used. The links may be adjusted to change the trajectory of the front wheel as the suspension compresses. Additionally, the shock mounts may be moved to prevent any change in effective spring and damping rates resulting from a change in linkage geometry. To demonstrate the usefulness of the design, an experiment was performed to determine the pivot point height at which the energy dissipated from the rear shock was a minimum. At various pivot point heights, the bike was ridden on an inclined (6 percent grade) treadmill at 23.3 km/hr. Minimum energy was dissipated at a pivot height of 8.4 cm above the bottom bracket.