As a simple alternative solution to processes such as engine test bench or road simulator, C.R.M.T. has developed and patented the method “SYCADY” to measure on a vehicle, during a road test, the effective engine's power and its motion resistance. The test consists in recording, on a flat road or test track, the acceleration of the vehicle using the whole range of engine's speed and the deceleration with the engine declutched. These tests are then treated on a desktop computer. This paper presents basic principles of the method and of the apparatus. Then are discussed notions of accuracy and reproducibility and the various possible uses of the method are illustrated with results obtained on different kinds of earthmoving vehicles (passenger cars, trucks, racing cars…) with various types of engines (gasoline fueled, diesel, turbocharged or not).