Conference Paper

The Effect of Front Fork Compliance on the Stability of Bicycles

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Abstract

In this paper the effect of front fork compliance on uncontrolled bicycle stability is analyzed. First the benchmark model of a bicycle is improved to take into account either torsion compliance or bending compliance of front fork, a lumped element approach is adopted introducing additional joints restrained by rotational springs and dampers. Two models having three degrees of freedom are developed and implemented in MATLAB codes to perform stability analysis. Then series of experimental tests are carried out on an advanced carbon fork and a standard steel fork, the modal analysis approach is adopted. Experimental methods and results are presented and discussed. A specific method is developed for identifying the stiffness and damping properties from the bending and torsion modes of the forks. Results obtained with the proposed method agree with data presented in literature. Finally, the identified stiffness and damping parameters are implemented in the simulation codes and some numerical simulations are carried out. Results presented in the paper show a small influence of torsion compliance on stability and a large influence of bending compliance on high speed stability. Copyright © 2015 by ASME Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal

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... In addition, new models including tire properties were developed [2][3][4] which made possible the study of high speed wobble [5]. Also, the WCBM has been improved with new features like the rider's dynamics [6,7] and front fork compliance [5,8]. Nowadays, although many interesting results have been presented, it is still difficult to recognize the rigid body properties (geometry and mass distribution) that have the largest effect on stability and to define and identify the critical compliances of frames, forks and wheels that influence stability. ...
... The second is bending compliance of the fork in the lateral direction. Since preliminary modal tests [8] showed that, owing to front fork geometry, wheel spindle moves almost perpendicularly to the steer axis, this compliance displaces the wheel in the lateral direction. The third is the torsion compliance of the frame that rotates the head tube causing both a lateral displacement and a rotation of the front assembly. ...
... The condition on the lateral displacement ( ) is described in Eq. (8). ...
Conference Paper
The effect on stability of mass, geometric and stiffness parameters of a bicycle with compliant frame, fork and wheel is studied. Critical stiffnesses of the structural elements are identified by means of specific experimental tests based on modal analysis and static stiffness measurement. Numerical stability analysis is carried out by means of a MATLAB code and simulations are planned with the design of experiment (DOE) approach. Numerical results show that the rigid body properties that have the main influence on stability are front wheel radius, longitudinal position of the center of mass and trail. Compliance of structural elements strongly affects the weave mode, which becomes unstable at high speed, but have a small effect on self-stability.
Article
Some studies of bicycle dynamics have applied the Whipple Carvallo bicycle model (WCBM) for the stability analysis. The WCBM is limited, since structural elements are assumed to be rigid bodies. In this paper, the WCBM is extended to include the front assembly lateral compliance, and analysis focuses on the study of the open loop stability of a benchmark bicycle. Experimental tests to identify fork and wheel properties are performed, this data is used in the stability analysis for ranking the influence of design parameters. Indexes from the eigenvalues analysis are applied in a full factorial approach. The results show that introducing front assembly compliance generates a wobble mode with little effect on self-stability. The forward displacement of the centre of mass of the rear frame and the increment in trail lead to large increments in the self-stability, whereas increments in front wheel radius and wheelbase reduce stability.
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