BRAKES DECOUPLING

In "Wheel Trajectories" the problem of how to design a front suspension for comfort (for which the wheel centre should ideally move in an upwards / rearwards direction) and to prevent pitching due to braking (for which the contact patch should ideally move in an upwards / forwards direction) was discussed. The two appear to place contradictory requirements on the way in which the wheel must move when the suspension is compressed.

The solution adopted for the Interconnected Suspension Bicycle project is to firstly design the suspension kinematics to give the wheel centre an upwards and rearwards trajectory which should help to achieve good comfort levels – and to mount the brakes in such a way as to transmit the brake forces back to the frame via an independent mechanism – one that prevents pitching when the brakes are applied.

This feature is called "brakes decoupling" because it decouples the brake anti-dive from what it would have been had the brakes been mounted in a conventional way.

This has been done by mounting the calliper to a separate linkage, a brake reaction lever which is attached to the base of the front forks via bearings that are concentric with the wheel bearing axis.

The brake reaction link (click image to enlarge)

The forces transmitted to the brake reaction lever are then in turn transmitted to the suspension upper link via another link – the brake reaction link. See image to left...

By this means, the anti-brake dive is completely independent of the wheel trajectory, so the suspension can be optimised for both comfort and anti-dive. Unlike a conventional fork, brake pitching doesn’t have to be controlled by increasing the suspension stiffness and damping, a palliative used on many current designs to the obvious detriment of ride quality and steering control. The excessive stiffness of front suspensions leads to a tendency for the whole front end to bounce off objects in the track, causing the tyre to become airborne and steering control to be lost.

In the clip, it is clearly seen that a bike with conventional suspension fails to absorb the energy of the impact resulting in the front wheel losing contact with the ground for quite some time. If a series of bumps like this were to be encountered, loss of steering control would be dramatic.

With the Interconnected Suspension Bicycle negotiating the same obstacle at the same speed (25 kph), the front tyre regains contact with the ground much sooner. Steering control is commensurately better.

As a consequence of the decoupling feature, the suspension stiffness and damping can be optimised for ride comfort and steering control without the additional constraint of having to prevent brake dive.