BMW Paralever

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Revision as of 14:02, 9 August 2010 by Budlight (talk | contribs)
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Introduction

The Paralever suspension was introduced on the 1988 R80GS and R100GS, then used on the 4-valve K and Oilhead bikes (except the R1200C). Whereas the original Monolever system had a single pivot at the front of the swingarm, like most motorcycles, the Paralever uses two links to connect the rear drive to the transmission. This is a "Four-bar" linkage, similar to double-wishbone suspension in cars which keeps the rear drive at a constant angle as the suspension moves. In fact, there are several similarities between the two that can be explored.

Monopara.gif

Let's be clear on some terms I'll use here. The "rear drive" is the bevel-gear containing casting that is at the end of the swingarm; it contains the flange that the wheel bolts up to. Whenever I refer to "rotation", I am specifically referring to the rotation, or angular change in position, of the rear drive unit as the suspension moves up and down. The wheel rotates while you ride but that's not important, and the Paralever links rotate around their end points also, but don't let that distract you. We are only concerned with the change in the angle of the rear drive unit (shown as a circle in the wireframe diagrams).

Also, I will mention the forces acting on the rear drive: there is a road force (pushes forward on the tire's contact patch during acceleration) and this is balanced by the inertial force of the bike which pushes backwards at the swingarm pivot. These two forces, since they are not directly opposing each other, create a twisting force or torque in the swingarm/drive/wheel assembly that we're looking at.

Torque.gif