Mountain Bike Rear Suspension Design: Utilizing a Magnetorheological Damper for Active Vibration Isolation and Performance

The introduction of suspension systems to mountain bikes began in the late 1980's and early 1990's. These suspensions created two types of mountain bikes; the hardtail and the full suspension mountain bike. However, designers of full suspension bikes must balance the need for pedaling efficiency, which calls for a stiff suspension, with comfort and trail contact, which calls for a soft suspension. This thesis presents experimental and theoretical results from the development of a rear suspension system that has been designed for a mountain bike. A magnetorheological (MR) damper is used to design a rear suspension system that can balance the need of ride comfort through shock absorption and performance characteristics such as handling and pedaling efficiency by using active control. Two control algorithms have been tested in this study – on/off control and proportional control. The damping was adjusted by setting the damper current to different levels in order to measure the effects of the change in response of the bike. The rear suspension system has been integrated into an existing bike frame and tested on a shaker table as well as a mountain trail. Shaker table testing demonstrates the effectiveness of the damper, while the trail testing indicates that the MR damper-based shock absorber can be used to implement different control algorithms. The shaker table and trail testing results indicate that active damping control can be implemented using an MR damper. Using the results of these experimental tests, a theoretical test was simulated using a mathematical model; which was used to represent the mountain bike mounted to the shaker table. The results were plotted using transmissibility, power spectrum density, and frequency mode shape plots which indicated three applicable natural frequencies near 5, 9, and 10 Hz, when applying the mountain bike, rear suspension system, and rider weight/distribution used for this experiment. Upon the analysis using MATLAB, the mathematical model was determined to correctly represent the overall dynamics of the bicycle pertaining to the sprung mass. Additional accelerometers will need to be placed throughout the bicycle to determine if the mathematical model correctly represented the overall dynamics of the bicycle as a whole.