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Gazza,
The rising rate suspension only has to do with the suspension, converting the wheel movement caused by bumps into differential rates of movement of the spring /damper over the stroke of the damper. The caliper mounting arrangement, fixed to the swinging arm or floating is not affected.
A floating rear caliper HAS to be a parallelogram arrangement with the rider on board and the ride height set correctly. The distance between the centre of the wheel spindle and the centre of the brake pad is fixed, the distance between the centre of the swinging arm pivot and the centre of the wheel spindle is fixed (provided the wheel is tight) and the the distance between the centre of the swinging arm pivot and the front fixing point on the crankcase is fixed. The length of the reaction rod is obviously not changeable. When the suspension moves up and down the caliper mount will move through an arc prescribed by the distance between the centre of the wheel spindle and the centre line of the pad. That number of degrees in that arc for any given suspension movement should be as close as possible to the same number of degrees that the contact patch of the rear tyre moves with the same suspension movement. If the arrangement is not parallel at the normal ride height with rider on board then the caliper and the contact patch between the pad and the disc will move outside that arc and the tyre contact patch is not free to rotate purely as a result of suspension movement and the suspension is also effectively locked when the brakes are locked. The system is not mechanically perfect because at extreme (up or down) suspension movements because the arrangement cannot remain parallel with 4 fixed lengths and 3 fixed points. That is my understanding anyway if what I have wrote makes sense????
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