Mountain bicycle with rear suspension having neutral braking trajectory
A rear wheel suspension system pivotably attached to a bicycle. The suspension system has an upper link attached to a main frame at a first pivot point, and a rear stay member attached to the upper link at a second pivot point. A lower link is attached to the main frame at a third pivot point, and is pivotably attached to the rear stay member at a fourth pivot point. A shock absorber is pivotably connected to the upper link and to the main frame. An instantaneous center of rotation (ICR) is defined where an upper axis extending through the first and second pivots intersects a lower axis extending through the third and fourth pivots. The ICR displaces along a trajectory from behind the bottom bracket, through an inflection point at which the upper axis and the lower axis are parallel, to in front of the bottom bracket, as the shock absorber compresses.
1. A bicycle, comprising:
a main frame including at least a seat tube, a top tube, a head tube, a down tube, and a bottom bracket fixed to at least one of the seat tube and the down tube; and
a rear wheel suspension system pivotably attached to the main frame, the rear wheel suspension system comprising:
an upper link pivotably attached to the main frame at a first pivot point;
a rear stay member having an upper end pivotably attached to the upper link at a second pivot point and a lower end having a dropout receiving a rear wheel axle of the bicycle;
a lower link pivotably attached to the main frame at a third pivot point located on said main frame at a lower vertical elevation than the first pivot point, and the lower link being pivotably attached to the rear stay member at a fourth pivot point located on said rear stay member below said upper end thereof; and
a shock absorber having a first end pivotably connected to the upper link and a second end pivotably connected to the main frame, the shock absorber operating between an uncompressed configuration and a fully compressed configuration;
wherein an instantaneous center of rotation is defined at an intersection between an upper axis extending through the first and second pivots and a lower axis extending through the third and fourth pivots, the instantaneous center of rotation displacing along a trajectory as the shock absorber operates between the fully extended configuration and the fully compressed configuration; and
wherein, as the shock absorber and thus the rear wheel suspension compresses from the fully extended configuration to the fully compressed configuration, the instantaneous center of rotation displaces from a first position located rearward of the bottom bracket to a second position located in front of the bottom bracket, and wherein the instantaneous center of rotation travels through an inflection point between the first and second positions, the inflection point corresponding to a position where the upper axis and the lower axis are parallel to each other and the instantaneous center of rotation is defined at infinity.
2. The bicycle according to claim 1 , wherein before reaching the inflection point, the instantaneous center of rotation moves along the trajectory away from the bottom bracket as the shock absorber compresses, and remains rearward of the bottom bracket.
3. The bicycle according to claim 2 , wherein after passing the inflection point, the instantaneous center of rotation moves along the trajectory toward the bottom bracket as the shock absorber compresses, while remaining forward of the bottom bracket.
4. The bicycle according to claim 1 , wherein the instantaneous center of rotation is disposed behind the bottom bracket upon the shock absorber travelling between about 30% to about 40% of a travel distance of the shock absorber from the extended configuration.
5. The bicycle according to claim 1 , wherein a suspension rate of the rear wheel suspension system decreases for a first portion of a travel distance of the shock absorber from the extended configuration.
6. The bicycle according to claim 5 , wherein the suspension rate increases for a remaining portion of the travel distance after the first portion.
7. The bicycle according to claim 5 , wherein the first portion is approximately 15% of the travel distance.
8. The bicycle according to claim 5 , wherein the decrease of the suspension rate along the first portion corresponds to a displacement of the instantaneous center of rotation from behind the bottom bracket to the inflection point.
9. The bicycle according to claim 6 , wherein the increase of the suspension rate along the remaining portion corresponds to a displacement of the instantaneous center of rotation from the inflection point to in front of the bottom bracket.
10. The bicycle according to claim 1 , wherein the rear stay member rotates in a direction opposite to a direction of rotation of the rear wheel relative to the main frame.
11. A rear wheel suspension system pivotably attachable to a main frame of a bicycle, the main frame having at least a seat tube, a top tube, a head tube, a down tube, and a bottom bracket fixed to at least one of the seat tube and the down tube, the rear wheel suspension system comprising:
an upper link pivotably attachable to the main frame at a first pivot point;
a rear stay member having an upper end pivotably attachable to the upper link at a second pivot point and a lower end having a dropout receiving a rear wheel axle of the bicycle;
a lower link pivotably attachable to the main frame at a third pivot point located on said main frame at a lower vertical elevation than the first pivot point, and the lower link being pivotably attached to the rear stay member at a fourth pivot point located on said rear stay member below said upper end thereof; and
a shock absorber having a first end pivotably connected to the upper link and a second end pivotably connectable to the main frame, the shock absorber operating between an extended configuration and a compressed configuration;
wherein an instantaneous center of rotation is defined at an intersection between an upper axis extending through the first and second pivots and a lower axis extending through the third and fourth pivots, the instantaneous center of rotation displacing along a trajectory as the shock absorber operates between the extended configuration and the compressed configuration, and wherein as the shock absorber begins to compress from the extended configuration, the instantaneous center of rotation displaces from behind the bottom bracket, through an inflection point at which the upper axis and the lower axis are parallel, and to a location in front of the bottom bracket as the shock absorber continues to compress to the compressed configuration.
12. The rear wheel suspension system according to claim 11 , wherein before reaching the inflection point, the instantaneous center of rotation moves along the trajectory away from the bottom bracket as the shock absorber compresses, and remains rearward of the bottom bracket.
13. The rear wheel suspension system according to claim 12 , wherein after passing the inflection point, the instantaneous center of rotation moves along the trajectory toward the bottom bracket as the shock absorber compresses, while remaining forward of the bottom bracket.
14. The rear wheel suspension system according to claim 11 , wherein the instantaneous center of rotation is disposed behind the bottom bracket upon the shock absorber travelling between about 30% to about 40% of a travel distance of the shock absorber from the extended configuration.
15. The rear wheel suspension system according to claim 11 , wherein a suspension rate of the rear wheel suspension system decreases for a first portion of a travel distance of the shock absorber from the extended configuration.
16. The rear wheel suspension system according to claim 15 , wherein the suspension rate increases for a remaining portion of the travel distance after the first portion.
17. The rear wheel suspension system according to claim 15 , wherein the first portion is approximately 15% of the travel distance.