TRANSMISSION

The torque delivery from the pedals is never smooth, particularly in lower gears when the demand for torque is high – such as when accelerating hard or going up hills. Consequently the bike and rider tend to accelerate and decelerate cyclically in harmony with the transmission torque causing weight to transfer forwards and backwards due to the changing acceleration resulting in pitching / bobbing of the bike and rider.

On a conventional bike, nothing can be done to stop the front suspension from bouncing up and down due to the weight transfer other than to stiffen the springs and tighten the damping until it ceases to be a problem (another reason why front suspensions are much stiffer and more tightly damped than is required for good ride and steering control – see also Brakes Decoupling"). At the rear, designers can use a property of the suspension called anti-squat by which some or all of the weight transfer can be reacted by forces in the suspension linkages to prevent cyclic pitching (or bobbing) – partially or completely.

Similar to brake anti-dive, anti-squat relates to the direction in which the rear contact patch moves as the suspension is compressed (with the transmission fixed). Anti-squat is positive (i.e. resists bobbing) when the contact patch trajectory is upwards / rearwards.

Transmission (click image to enlarge)

Ideally this should be achieved without feeding back excessive forces into the chain as this leads to unwanted kick back into the pedals resulting from sudden movements of the suspension. On the Interconnected Suspension Bicycle this is achieved by passing the chain from the bottom bracket through the rear suspension pivot centre, so changes in suspension position do not result in any changes to the chain tension. See image on left...

If we return to the bogie analogy used on the "Interconnection"" page, it is seen that insufficient anti-squat (shown by an arrow at a low angle to the ground) leads to pitching / bobbing as previously described however, if the anti-squat line passes through the centre of stiffness, pitching / bobbing can be eliminated entirely. The vertical component of the anti-squat force acts on the vertical stiffness of the suspension causing a small amount of vertical displacement which goes more or less undetected.

The really interesting feature of the transmission on the Interconnected Suspension Bicycle is that the very high levels of anti-squat serve not only to eliminate any contributions to bobbing from the rear suspension, but also from the front suspension. The anti-squat forces act through the interconnection to eliminate bobbing from both ends.

Furthermore, it was mentioned previously that the requirements of comfort and anti-brake pitch are complimentary and are met by a simple trailing arm with a high pivot point. Add to this that the interests of anti-squat are also served well by this simple design and it can be seen that nothing more complex is required.