The Shimano Dura-Ace (7900) was totally overshadowed by its electronic Di2 cousin, the Dura-Ace (7970). What could you say about yesterday's mechanical steam-punkery - when there was tomorrow's digital universe to boldly explore?

In fact, quite a lot. The Dura-Ace (7900) was the first Dura-Ace to incorporate a carbon p-knuckle and a composite pulley cage. The, all aluminium, Dura-Ace (7800) had weighed in at a portly 182g, a figure that was being severely challenged by the new SRAM Red and by Campagnolo's move to plaster their derailleurs with highly visible carbon fibre. The use of composites allowed the Dura-Ace (7900) to come in at a very competitive 169g and, in typically understated Shimano style, it did it without the tell-tale carbon weave being visible anywhere. Technology should be for connoisseurs, not for boy-racers.

And then there was the look and finishes. The Dura-Ace (7800)'s mirror polished metal finish would have been a difficult look to seamlessly spread across both aluminium and carbon composite. It would also have tended to reveal, rather than conceal, the slightly ungainly mechanical complexity of Di2 systems. A new design language was needed, and here it is. I like the dark matte grey and the polished highlights. But I do find the high gloss, sparkly, black pulley cage plates odd. Should they not also have been matte? Why is the temperature of the warm black different from that of the cool grey on the body? And what's with the sparkle?

People kept telling me that there were at least two different generations of Dura-Ace (7900). I was slightly unconvinced - I certainly did not notice any changes at the time. But on closer inspection I have found that there are two slightly different inner pulley cage plates.

This example is an early version - with an inner pulley cage plate with no reinforcing ring around the mount for the rear-most aluminium pillar.

And talking of carbon composite inner pulley cage plates, I would note that this example, like many others in this collection, is thoroughly chewed up. The battle between hardened steel chain links and even a high-tech lightweight plastic has only one winner.

• Derailleur brands: Shimano
• Categories: Shimano - the Dura-Ace story
• Country: Japan
• Date of introduction: 2008
• Date of this example: 2008 (two letter date code is 'GF')
• Model no.: 7900 SS
• Weight: 169g
• Maximum cog: 28 teeth
• Total capacity: 33 teeth
• Pulley centre to centre: 56mm
• Index compatibility: 10 speed
• Chain width: 3/32”
• Logic: top normal
• B pivot: sprung
• P pivot: sprung
• Materials: carbon p-knuckle and pulley cage, the rest is aluminium

Ref. 1662