A research has been done on coupled two-carrier planetary gear trains built with spur gears which consist of two coupled and four external shafts and enable two-speed transmissions. The influence of different variants of planetary gear trains with related basic parameters on their basic characteristics has been systematically studied. The influence of ideal torque ratios for the planetary stages on speed ratios in both speed drives has also been studied. Kinematic changeable possibilities of each variant have also been designed. Expressions are defined for the determination of the ideal torque ratios for the planetary stages considering requested transmission ratios which resulted in the creation of the basis for synthesis of two-speed planetary gear trains. Kinematic schemes have been created and they clearly show the shaft and gears arrangement of different variants of planetary gear trains. Extreme values of ratio of transmission ratios of different variants of planetary gear trains have been determined and variants have been identified which from the aspect of possible transmission ratios that can be implemented. Expressions have been deduced for the determination of the efficiency of planetary gear trains and analyses of the efficiency of the designated variants have been conducted. The experimental determination of the efficiency has been carried out on experimental planetary gear trains for the purpose of proving the validity of the deduced mathematic-mechanical models. Variants of planetary gear trains have been found, where unacceptable specific angular speed of satellites might occur. Specific torques on the sun gear of various planetary gear trains has been defined, which enable dimensioning gears of planetary stages. A software program has been developed for the analysis, synthesis and evaluation of results as well as for finding out the optimal variant of planetary gear trains with related basic parameters.