Shimano aero dynamics

Shimano aero dynamics front cover main image

Aerodynamics was Shimano's big thing for the 1981 model year - and it was huge. Shimano spent more marketing money on promotion than we had ever seen spent on any set of mere bicycle components before. If you worked in a bike shop (as I did) this, impressively glossy, brochure was the centrepiece of the campaign. It was loaded with slightly tenuous science and on page 9 and page 10 features a big equation describing air resistance. Dating from a time before 'desktop publishing' the Greek letter Rho looks charmingly hand drawn. In 1981 no one I had ever met had used the word 'font' to describe anything other than an oversize bird-bath for baptising babies.

The derailleurs featured represent the full aero range, with the same series numbers as the derailleurs that were actually produced, but I think that they are all prototypes. In particular they have an unfamiliar screw above the b-pivot that is used to tune the number of sprockets that can be selected. On the production models this screw was neatly incorporated into the b-knuckle and was below the b-pivot. The range is:

  • Shimano Dura-Ace AX (7300) prototype
  • Shimano 600 AX (6300) prototype
  • Shimano Adamas AX (AD10) prototype
  • Shimano Positron AX (AX10) prototype

People often forget that all the derailleurs in the AX series were indexed. The Dura-Ace AX (7300) was the first ever indexed Dura-Ace derailleur - not the more famous, but later, Dura-Ace (7400). Geeks will be interested in the description of the indexing system on page 19. This system depended on a set of tiny steps cut into an element of the rear derailleur. These tiny steps seemed to be inevitably destined to wear and become imprecise - but I never knew anyone who used an AX series derailleur for long enough to find out if this really happened.

As for the silver suited cyclists riding their futuristic bikes clad in aerodynamic components - they had clearly escaped from a secret government facility in Roswell, New Mexico.

  • Publisher: Shimano
  • Country: Japan
  • Date: January 1981
  • Derailleur brands: Shimano
  • Derailleurs: Shimano Dura-Ace AX (7300) prototype, Shimano 600 AX (6300) prototype, Shimano Adamas AX (AD10) prototype, Shimano Positron AX (AX10) prototype