The ‘x’ in SunTour Vx was widely understood as standing for ‘extra light’ (I do not know whether this was SunTour’s real intention). This was the SunTour V Luxe after it had been on a strenuous diet, the steel holder for the cable clamp bolt has been replaced by an aluminium channel and the knuckles are slimmer and neater.
Despite the weight loss, this was an extremely affordable, strong and reliable derailleur - I still see many of these in use on the roads today.
The plain Vx is the short arm version, and at 205g it was a viable racing gear (a Campagnolo Nuovo Record weighed 198g) - however pride and snobbery meant that the Vx was only widely used on training bikes.
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