With the Scrambler, SunTour introduced yet another mid-end indexing mechanism. This is a system based on an indexed lever, with the rear derailleur merely centred with a single adjusting screw, and with a ‘Light Action’ type spring built into the cable clamp mount. It is possibly the fourth indexing system Suntour introduced within a decade - not a good idea.

Heavy, ugly and not particularly cheap, no one was very interested.

But three features catch my eye:

• The pulley cage plates have a ninja/sci-fi look.
• It has an unusually large, 12 tooth, guide pulley.
• The centre of the guide pulley is offset from the p-pivot by a tiny amount - echoing a geometry that SRAM would later use on their ESP designs.

I think that this particular example is a later version with the following traits:

• The knuckles are black.
• The main Allen bolts are black.
• The writing on the outer parallelogram plate is silver on black.
• The pulley wheels are grey.

• Derailleur brands: SunTour
• Categories: SunTour - indexing insanity
• Country: Japan
• Date of introduction: 1988?
• Date of this example: 1988 (two letter date code is ED)
• Model no.: SR21
• Weight: 332g
• Maximum cog: 32 teeth?
• Total capacity: 34 teeth?
• Pulley centre to centre: 65mm
• Index compatibility: 5 speed?
• Chain width: 3/32”
• Logic: top normal
• B pivot: unsprung
• P pivot: sprung
• Materials: aluminium knuckles, steel parallelogram plates and pulley cage plates