Why is a gearbox necessary?
Yeah. Gearbox very important!
Control over power output, by means of the throttle pedal, simply regulates the rate at which the engine is doing work: at very high speeds.
the torque output can at the same time be significantly less than at considerably lower speeds. In other words, maximum torque may be available over only a very limited speed range. Consequently, one needs to be able to regulate both the power output and the speed range of the engine relative to the range of speeds over which the vehicle is at any given time likely to be required to operate. Only in this way can the torque at the wheels be balanced against demands for either a steady speed uphill or downhill, or on the level, or for acceleration or deceleration. A gearbox is necessary, therefore, so that the driver can regulate torque by selecting the appropriate speed range or, in other words, the vehicle speed at which maximum torque is obtainable.
When a vehicle is moving at a uniform speed, the driving force, or tractive effort, at the wheels must be such as to exactly balance the sum of three categories of variable forces tending to oppose the motion. If it is greater, the car will accelerate, and if it is smaller, it will decelerate until a balance is obtained. Such a balance will be established eventually, because two of the forces vary with speed. The three forces are: (1) aerodynamic, or air, resistance; (2) gradient resistance, which can be either positive or negative; and (3) rolling
resistance.
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