title: Mountain bicycle rear suspension dynamics and their effect on cyclists
Creators: name: Titlestad, John Karl
Publisher: name: University of Glasgow
Year: 2001
Subjects: subject: Mechanical engineering.

description: The research documented in this report was conducted to understand better the anomaly between the predicted benefits of rear suspension systems for mountain bicycles and the preferred choice of rigid framed mountain bicycles by professional cyclists in the Union Cycliste Internationale (U.C.I.) world cup and world championship events. To investigate the effects of rear suspension systems, a rig was designed on which two mountain bicycles were tested, one with (SU) and one without (HT) a rear suspension system. The purpose of this rig was to isolate the effects of rear wheel impact in order to conduct comparative performance tests of the bicycles with a number of cyclists. The rig held the front forks of the bicycle under test vertical and stationary while the rear wheel travelled on a large diameter roller. 'No bump' tests were conducted with the roller covered by carpet and with a drag load provided by a friction belt, while for the 'bump' tests wooden strips were attached across the surface of the roller and the friction belt was removed. Subjects, aged 22.3 +/-2.54 years, performed bump and no bump tests with both bicycles under sub-maximal conditions. The physiological and psychological effects on cyclists riding the two types of bicycle on the simulated track of the rig were measured by the cyclists' oxygen consumption (VO2), heart rate, RPE (Borg 6-20 scale), and comfort (scale 1-5) rating. The dynamic behaviour of the bicycles was also observed by measuring the vertical acceleration of the saddle and handlebars, the chain tension, tangential crank velocity at the pedals, the force applied to the front mounting braclcet and the tangential surface velocity of the roller. A DADS model of the bicycle/rider dynamics was developed and the results from this model were compared with the measured dynamic behaviour of the two bicycles. Results from the bump tests show a significant advantage for the SU bicycle over the HT bicycle in oxygen consumption (9.14 ml -- kg-1--min-1, P &lt; 0.001), heart rate (34.43 beats -- min-1, P &lt; 0.001), energy expenditure (14.43 KJ-- min-1), RPE (1.83, P &lt; 0.05), comfort (1.87, P &lt; 0.001), maximum saddle and handle bar acceleration (1.45 and 0.54 g's respectively) and displacement (11.8 and 7.5 mm respectively), maximum and mean pedal force (122 and 59 N respectively) and mean pedal power output (64 Watts), and the horizontal force of bump impact measured at the front mounting bracket (197 N). During the no bump test there was a small (2.18 ml o kg-1 o min-1 and 2.97 KJ o min-1 respectively) but significant (P &lt; 0.005 and P &lt; 0.025 respectively) increase in oxygen consumption and energy expenditure of the subject on the SU bicycle but no significant difference between the bicycles in the heart rate, RPE or comfort of the subject. There was a significant (P &lt; 0.025 and P &lt; 0.05 respectively) but small increase in the maximum and mean pedal force (34 and 16 N respectively) and mean pedal power output (14 Watts, P &lt; 0.025) for the HT bicycle. There was no significant difference between the other mechanical values. The physiological, psychological, mechanical and simulation results correlated well for the bump test. The results from the rig simulation confirmed that energy was lost from each bump impact and proved a useful tool in the analysis of the mechanical results, with which they correlated well. The physiological and mechanical results show that the SU bicycle offers significant advantages over the HT bicycle during the bump test. The results for the no bump test do not correlate for some variables, but the differences are very small between the two bicycles.