Selection of powertrain for vehicle is depends upon vehicle type & application of vehicle. To achieve performance of vehicle, engine torque at maximum revolutions, Transmission ratio, Axle ratio & tire plays important role. In order to understand vehicle performance in theoretical calculation there should be proper selection of power train aggregates. All these aggregates technically will evaluate the actual vehicle performances. For example, trucks are seldom run at their rated maximum speed. In fact, they are usually operated with engine speed at maximum torque or at the speed where fuel consumption is minimized. In climbing hills, there may be occasions when the engine revolution is raised to its maximum to produce the maximum horsepower; however, the most efficient method of operation is to use the range of engine speed, which maximizes torque. If an engine's speed range, producing maximum torque, is extremely narrow, a slight increase of rpm will cause a substantial loss of power and sign of poor performance characteristic. In other words, engines with high maximum torque and horsepower are not necessarily the most "powerful engine." Factors other than the maximum values of the torque and horsepower must be evaluated in determining the practical performance of engines. Furthermore, a high performance engine must be combined with the correct transmission and differential in order to produce the desired running performance. It is necessary to understand the factors affecting its ease of operations. This Paper tells how to integrate powertrain and judge performance of vehicle according to application and type of vehicle by reading performance curves and calculation