The Suntour Gran-Prix introduced the slant parallelogram to the world. It is the most famous of the many brain-children of Nobuo Ozaki, SunTour’s legendary chief designer. The idea is brilliantly simple - as the pulley cage moves inwards, it also moves downwards, following the shape of the freewheel and maintaining a reasonably constant chain gap. Virtually every modern derailleur of any quality uses this design. The 1964 patent on this design (US patent # 3,364,762) allowed SunTour to gradually dominate the derailleur industry, until it ran out in 1984.
The SunTour Gran-Prix was also notable in a number of other ways.
It fits a Campagnolo hanger (and has an adjustment screw) - starting the Japanese move away from Huret (SunTour’s original choice) and Simplex (Shimano’s original preference). The hanger plate on this example is particularly unusual with two holes for drop-out bolts - but it has the tell-tale Campagnolo tag position.
The Gran-Prix is low-normal (‘Rapid Rise’ in Shimano-speak). And, in addition, it uses SunTour’s unique single spring design - the same spring operates the parallelogram and also tensions the chain. These last two features are a touch too mad for my tastes - and I have never found low normal gears to be very positive - whether they are the ancient, cheapo, SunTour Skitter or the ultra-modern, fantastically refined and expensive Shimano XTR.
Finally the Gran-Prix illustrates a problem with naming a product in an alien character set. Sometimes SunTour labelled the actual derailleur as a Gran-Prix, sometimes as a Grand-Prix, and, on at least one occassion they advertised it as a Grand Prix (without the hyphen) - all of which should be just enough to avoid having to pay royalties to the impishly charming Bernie Ecclestone.
One of my ‘derailleurs that changed the world’.
Browse associated documents.