The Bridgestone SMS Max was Bridgestone's second attempt at indexing a 5 speed derailleur. Compared to the earlier Bridgestone Synchro Memory Shift, the cylinder that contains the indexing cam has been reduced in size (from 36mm to 30mm diameter) and the b-knuckle is geometrically simpler to manufacture, fits a conventional Campagnolo drop-out and incorporates a high and low gear stop screw (which were missing from the Bridgestone Synchro Memory Shift).
This example is the long cage, ‘GT’ version. It has one of the most interesting pulley cage designs in this collection. The guide pulley pivots around the normal, sprung p-pivot in a fairly normal way, although it has a large (37mm) offset from this pivot. The tension pulley, however, is mounted in a separately pivoting piece of pulley cage, sprung by the same spring, but with a softer action so that it articulates before the guide pulley. This means that for the higher gears the guide pulley stays in the same place relative to the pivot, but for lower gears it starts to rotate around the pivot, moving away from the wheel axle. This could be a very clever design, maintaining chain gap quite well on wide ratio freewheels which tend to have top cogs that are relatively similarly sized, but the bottom cogs that are very different sizes from each other. During the late 1970s Bridgestone took out a large number of patents covering different designs of articulated pulley cages like this one. In many ways they foreshadow SunTour's Tech pulley cage designs.
Smart, but immediately consigned to the dustbin of history.
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