Coupled suspension system for bicycles

1. A bicycle, comprising:

at least one frame defined in a principal plane; which comprises an upper steering tube defined with respect to an upper axis that is part of the main plane, and a lower steering tube defined with respect to a lower axis that forms part of the main plane and is significantly collinear with the upper axis;

a handlebar assembly attached to the upper steering tube of the frame in such a way that at least a relative rotation between the handlebar assembly and the upper steering tube is allowed with respect to the upper axis, but relative displacements between the handlebar assembly and the upper steering tube are limited at least in directions perpendicular to the upper axis;

a fork attached to the lower steering tube of the frame so that the fork has the same degrees of freedom relative to the lower axis between the fork and the lower steering tube as the degrees of freedom between the handlebar assembly and the upper steering tube with respect to the upper axis; and

a means for rotation transmission for transmitting at least partially a rotation of the handlebar assembly with respect to the upper tube in a rotation of the fork with respect to the lower tube,

wherein a vertical flexibility of the frame between the upper steering tube and the lower steering tube is greater than a sum of a vertical flexibility of the handlebar assembly between a point of attachment of the handlebar assembly to the upper steering tube and any other point of the handlebar assembly, and a vertical flexibility of the fork between a point of attachment of the fork to the lower steering tube and any other point of the fork.

2. The bicycle according to claim 1 , in which the attachment of the handlebar assembly to the upper steering tube of the frame limits all relative movements and rotations except the rotation with respect to the upper axis, defining a handlebar plane that comprises the upper axis and coincides with the main plane when the bicycle advances in a rectilinear direction; and

in which the attachment of the fork to the lower steering tube of the frame limits all the relative movements and rotations except the rotation with respect to the lower axis, defining a fork plane which comprises the lower axis and coincides with the main plane when the bicycle advances in a rectilinear direction.

3. The bicycle according to claim 2 , in which the means for rotation transmission is composed of a first link joined to the handlebar assembly so that all relative movements and rotations are limited except the rotation with respect to the handlebar axis perpendicular to the handlebar plane; and

a second link joined to the fork so that all relative displacement and rotations are limited except the rotation with respect to the fork axis perpendicular to the fork plane, the first link and the second link being joined by joining means that limits all displacements, but allows rotation in more than one direction.

4. The bicycle according to claim 1 , in which the means for rotation transmission is a single body of controlled flexibility firmly attached to the handlebar and the fork, defining a joint rotation axis according to a junction point of the handlebar set with the upper steering tube and a junction point of the fork with the lower steering tube, and which works preloaded in extension so that the means for rotation transmission fixes the handlebar assembly and the fork with respect to the frame in a direction of the joint rotation axis, which together with a linear guide between the handlebar assembly and the fork, restricts all movements and rotations except the relative movement of the handlebar with respect to the fork on the joint rotation axis and the synchronized rotation of the handlebar and fork assembly with respect to the joint rotation axis.

5. The bicycle according to claim 1 , in which the means for rotation transmission is a single body with controlled flexibility firmly attached to the handlebar and the fork, defining a joint rotation axis according to a junction point of the handlebar set with the upper steering tube and a junction point of the fork with the lower steering tube, and which works preloaded in extension so that the means for rotation transmission fixes the handlebar assembly and the fork with respect to the frame in a direction of the joint rotation axis, restricting all movements and rotations except the relative movement of the handlebar assembly relative of the fork on the joint rotation axis and the synchronized rotation of the handlebar and fork with respect to the joint rotation axis.

6. The bicycle according to claim 2 , wherein the means for rotation transmission is located within a projected inner volume of the upper and lower steering tubes of the frame.

7. The bicycle according to claim 1 , in which a trajectory of a virtual pivot of rotation that defines the relative displacement of the lower steering tube with respect to the upper steering tube is delimited in a space that confers anti-dive characteristics greater than 0%.

8. The bicycle according to claim 1 , comprising a rear wheel attached to rear dropouts of the frame, a saddle assembly attached to a seat tube of the frame, and a set of pedals attached to a bottom bracket of the frame, and wherein a vertical flexibility of the frame between the rear dropouts and the seat tube is greater than a sum of a vertical flexibility of the rear wheel and the saddle assembly, and is at least an order of magnitude higher than a vertical flexibility of the frame between the bottom bracket and seat tube, and a vertical flexibility of the frame between the upper steering tube and the seat tube.

9. The bicycle according to claim 8 , in which the path of a virtual pivot of rotation that defines the relative movement of the rear dropouts with respect to the seat tube and bottom bracket is delimited in a space that confers anti-squat and brake-squat characteristics close to 100%.

10. The bicycle according to claim 8 , comprising:

a front absorber/damping means that controls a displacement of the lower steering tube with respect to a rigid assembly of the frame comprising the upper steering tube, the seat tube and the bottom bracket;

a rear absorption/damping means that controls a movement of the rear dropouts with respect to the rigid assembly of the frame; and

a crossed absorption/damping means that controls a displacement of the lower steering tube with respect to the rear dropouts.

11. The bicycle according to claim 8 , comprising:

a crossed absorption/damping means that controls a displacement of the lower steering tube with respect to the rear dropouts; and

a front absorber/damping means that controls a displacement of the lower steering tube with respect to a rigid assembly of the frame comprising the upper steering tube, the seat tube and the bottom bracket; or

a rear absorption/damping means that controls a movement of the rear dropouts with respect to the rigid assembly of the frame.

12. The bicycle according to claim 10 , in which a ratio between, a force ratio applied to the lower steering tube relative to a force applied on the crossed absorption/damping means, and a force ratio applied to the rear dropout relative to a force applied to the crossed absorption/damping means, is of similar magnitude to a ratio of forces applied on the lower steering tube and forces applied on the rear dropouts when pedaling.

13. The bicycle according to claim 7 , in which the trajectory of the virtual pivot of rotation is delimited in a space that confers anti-dive characteristics between 50% and 100%.

14. A bicycle, comprising:

at least one frame defined in a principal plane; which comprises an upper steering tube defined with respect to an upper axis that is part of the main plane, and a lower steering tube defined with respect to a lower axis that forms part of the main plane and is significantly collinear with the upper axis;

a handlebar assembly attached to the upper steering tube of the frame in such a way that at least a relative rotation between the handlebar assembly and the upper steering tube is allowed with respect to the upper axis, but relative displacements between the handlebar assembly and the upper steering tube are limited at least in directions perpendicular to the upper axis;

a fork attached to the lower steering tube of the frame so that the fork has the same degrees of freedom relative to the lower axis between the fork and the lower steering tube as the degrees of freedom between the handlebar assembly and the upper steering tube with respect to the upper axis; and

a rotation transmission device configured to transmit at least partially a rotation of the handlebar assembly with respect to the upper tube to a rotation of the fork with respect to the lower tube,

wherein a vertical flexibility of the frame between the upper steering tube and the lower steering tube is greater than a sum of a vertical flexibility of the handlebar assembly between a point of attachment of the handlebar assembly to the upper steering tube and any other point of the handlebar assembly, and a vertical flexibility of the fork between a point of attachment of the fork to the lower steering tube and any other point of the fork.