4X4

4x4, also called a ‘four wheel drive’ (4wd), is a vehicle in which the power is supplied to all the four wheels. The engine infrastructure ensures that the transmission is linked to the front wheels also, in contrast to the normal system of being linked only to the rear wheels. The four wheel drive system is generally used in all-terrain vehicles and off-road vehicles. Since four wheel driving uses a greater amount of fuel, the driver has the option of changing between the two-wheel drive for city roads and the four-wheel drive for unpaved roads or surfaces where there is less traction, like ice and loose gravel.

The four wheel drive vehicle is believed to have been born in the late 1800s through an idea of Ferdinand Porsche who designed a four wheel drive for his electric car. This car had an electric hub connected to each wheel. The first internal combustion engine four wheel drive vehicle was built in Amsterdam in 1903 by the brothers Jacobus and Hendrik-Jan Spijker. Later Daimler Benz, Mercedes, BMW and the Land Rover entered the four wheel drive segment.

A challenge when designing a four wheel drive vehicle is to permit the inner wheels to rotate at a different speed as compared to the outer wheels when taking a curve. If the transmission causes all the four wheels to turn at the same speed even when turning, it would result in skidding and improper control. To overcome this issue, a differential mechanism is used wherein one input shaft connects to two output shafts, maintaining a constant torque for all the wheels. Four wheel drive vehicles are very useful when driving over excessively uneven terrain, and the chances of the wheels getting stuck are high.