DISRAELI GEARS
The Shimano Dura-Ace AX (7300) is a riddle, wrapped in a mystery, inside an enigma. A ground-breaking technical tour de force with a silky smooth shift - that was reviled in the peleton as unreliable, fragile and tetchy. The subject of one of the most sophisticated, elegant, expensive and comprehensive marketing campaigns in the history of the cycle industry - that failed disastrously in the market. A unashamedly radical attempt to redefine the very nature of the derailleur - that ended up curiously derivative of Campagnolo and SunTour‘s designs. A no-expense-spared top-of-the-line piece of bike porn - with plastic pulley wheels without a sealed bearing or stainless steel tooth in sight and an all-up weight of around 220g. And last but not least, a Dura-Ace derailleur - that was clearly the bastard child of a Positron. Where to begin?
Let’s start with the ‘aero’ nonsense. There was much to admire about the Dura-Ace AX groupset’s aerodynamics, notably the small details like the brake cables routed in the handlebars, but the rear derailleur was not, and never could be, a big part of this. Sure it had a lower frontal area than usual, and sure it was composed of seductively smooth streamlined forms, but it is hard to see this having much affect in turbulently chaotic air that had been churned up by the front wheel, the rider’s feet and the passing spokes of the rear wheel.
And then there’s the geometry. From Campagnolo we get an unsprung rear knuckle with an in-line parallelogram. From SunTour we get a pulley cage that pivots around the axis of the guide pulley. From Positron we get indexing built into the derailleur. The cunning bit is a tiny set of steps on a steel element at the rear knuckle, which not only defines the six index positions, but also forces the derailleur to swing backwards as it moves inwards, kind-of maintaining the chain gap. It’s the same trick that the Campagnolo Croce d’Aune notoriously tried to pull-off some years later.
And finally there is the legacy. The Dura-Ace AX (7300) was a full-on commercial disaster - but is arguably one of the foundation stones of Shimano’s current success. It created a 'fear of being left behind' that forced every other derailleur manufacturer in the world to redesign their own derailleurs to incorporate ‘aerodynamic’ elements. With the European manufacturers already on their knees, and SunTour about to be clobbered by technical problems, this unnecessary expenditure crippled every one of Shimano’s competitors.
Shimano had a hugely profitable, high volume, low-end business and could easily afford the odd high-tech red herring - especially if it led the competition to their doom. It was an accidental version of Ronald Reagan’s Star Wars strategy - noisily adopt a technology that is so expensive that the Soviet Union financially implodes trying to catch up. Whether or not the Star Wars technology functioned (or even existed) is neither here nor there - ‘The Gipper’ probably didn’t know or care (or even understand the question).
In its short life the Dura-Ace AX (7300) went through at least 6 different variants. As far as I can tell, some of their distinguishing features might be as follows:
In addition to all this frenetic fiddling, Shimano appear to have two different designs for the curved steel cable guide at the b-knuckle, but these seem to have come and gone at Shimano's whim, without one design being clearly earlier or later than the other.
This is a, near perfect, example of the fourth version described above. Some key features are:
