So why separate the power from the wheel? Because of the different speed of the engine to be variable speed, the problem is more complex, I will not elaborate, in short, is a different speed of the engine gear to different speeds pass to the wheel, at this time you need to slow the gear and Wheel separate, with high-speed gear and wheel engagement, this one must use a clutch combination. Understand the working principle of the clutch, then to combine the actual. When your car at the start, the wheel is stationary, to make the car in motion to the state of rest, when the thrust is great, much larger than the car in motion, this time depressing the clutch, Hang a file to see what happened? When you step on the clutch, that is, ready to drive the wheels with gear, put a file, is the slow gear to the transmission, when you release the clutch, the slow gear on the wheel gear You lift fast, it depends on fast, you lift the slow, it depends on the slow, then the car started. If your clutch is lifted quickly, the two gears are immediately engaged. Since the car is stationary, the thrust required is high, and the power output from the engine is not sufficient to bring the car to a gear, then the car suddenly abruptly A move, and then turn off. When the car is running, it shows that the power of the engine has been transmitted to the wheel, but because the force to be overcome is greater than the force output by the engine, that is, the engine can not push your car, the gear is stuck and the engine stalls. So that's why when you start you have to throttle, lift the clutch slowly. Gasoline throttle can increase the power output of the engine, lift the clutch slow will reduce the resistance, so that the engine to overcome the static friction, so that the vehicle started smoothly. When the car is up, the clutch can be fully and slowly lifted, because after the car, the dynamic friction than the static friction when the car is much smaller. This is why the clutch in the second, third and fourth gear can be lifted faster without stalling. Similarly, the small slope starting to increase the throttle, clutch to twist is also the reason for this, because the slope of the resistance greater than the plane.