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Q: What is 4 Wheel Drive?

December 17, 2013 12:53 PM

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Cars can be designed so that the engine powers all four wheels. Vehicles that are designed in this manner are known as 4-wheel-drive and all-wheel-drive vehicles. If you've ever wondered how 4-wheel drive works or why it's beneficial, read on to learn more.

When a car engine is in operation, it produces a twisting motion called torque. Torque is a force that acts on all of the wheels of the car to make them move. If the car is a 4-wheel drive, the engine will produce torque that is applied to all four wheels. In ordinary 2-wheel drive cars, torque is applied only to the front wheels or the rear wheels.

4-wheel-drive systems can be part-time or full-time. A part-time system requires that the driver shift from 2-wheel drive into 4-wheel drive mode when the going gets rough or slippery, such as on snowy or icy roads. These vehicles are safer to drive during heavy rain or snowstorms because they allow all four wheels to look for grip, making skidding and hydroplaning less likely.

Full-time 4-wheel-drive systems called "all-wheel-drive" systems provide engine torque to all four wheels at all times. Virtually every 4-wheel-drive passenger vehicle -- cars, minivans and crossover SUVs -- are all-wheel drive. Most true off-road vehicles, on the other hand, use part-time 4-wheel-drive systems and also include a 4-wheel-drive "low" gearing range for when the off-roading gets really hairy. Military vehicles such as jeeps often use the more hardcore 4-wheel-drive systems so that they can travel in the desert or other areas where there are not usually roads.

Some of the advantages of 4-wheel drive include:

-- Greater grip and control of the vehicle on all surfaces. Whether you're driving on icy or very wet roads, or even bone-dry pavement, 4-wheel drive is safer.

-- The ability to drive on sand, in snow and over dicey terrain. Off-road vehicles need 4-wheel drive in order to be able to keep moving. Without a 4-wheel-drive system, these vehicles would lose traction and get stuck while driving in the desert, in deep mud or snow, or along the Rubicon Trail.

You should consider purchasing a 4-wheel drive vehicle. These vehicles are safer to drive in hazardous conditions and sometimes allow you the option of driving off-road as needed.

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