SunTour MounTech II GTL

SunTour MounTech II GTL derailleur main image

The SunTour MounTech was the first derailleur ever designed specifically for use on a mountain bike. Truly a milestone product. It was essentially the knuckles and parallelogram of the SunTour aRX with the addition of SunTour’s ‘Tech’ cage design. The result was a three pivot derailleur, with an unsprung pivot at the hanger and SunTour’s signature slant parallelogram. It gave a very small and consistent chain gap and a lightening quick and pin point accurate gear change.

I think this example is a MounTech II. It dispenses with the fatally unreliable guide pulley design of the original MounTech and adopts the more straight forward approach using a conventional guide pulley that is easy to replace that was pioneered by the Le Tech. It loses the ‘Quick Cage’ and gets a more rigid double sided pulley cage. The pulley cage and the link element go back to the lengths used in the SunTour Le Tech. All good stuff but, alas, by the time the MounTech II arrived on the market, SunTour’s whole ‘Tech’ programme had become tainted with the failings of the original MounTech design, and the MounTech II never had a chance.

A tragedy but it is worth noting that, despite the massive improvements built into this third generation design, this example is badly out of line. The ‘curse of Duopar’ strikes again.

A final point of interest is the appearance of the 12 tooth tension pulley. This is one of the earliest gears to exhibit the idea of using a large tension pulley to increase capacity for a given pulley cage length - an idea now widely adopted by Shimano.

  • Derailleur brands: SunTour
  • Categories: SunTour - the mountain bike gears, SunTour - Frank Berto and the curse of Duopar
  • Country: Japan
  • Date of introduction: 1985?
  • Date of this example: 1985 (two letter date code is BK)
  • Model no.: 5500
  • Weight: 276g
  • Maximum cog: 34 teeth (Source: Sutherlands fifth edition assuming 26mm dropout)
  • Total capacity: 40 teeth (Source: Sutherlands fifth edition assuming 26mm dropout)
  • Pulley centre to centre: 80mm
  • Index compatibility: friction
  • Chain width: 3/32”
  • Logic: top normal
  • B pivot: unsprung
  • P pivot: two, both unsprung
  • Materials: largely aluminium with steel pulley cage plates and inner parallelogram plate

Browse associated documents.

SR SUNTOUR - web site 2020

SR SUNTOUR - web site 2020

SR SUNTOUR - web site 2020 thumbnail