An automatic bicycle drivetrain shifting apparatus comprising a bicycle drive chain derailleur apparatus powered by a servo gearmotor and controlled through a highly adaptable user interface serving to automatically alternate drive chain position between available bicycle drive sprockets based on user preset and in real time modifiable criteria and additionally making use of critical chain driver apparatus serving to ensure chain motion is always available to satisfy derailleur operation requirements often prevalent during coasting and stopping where the bicycle speed changes while pedaling motion has ceased.