Q: What is All-Wheel Drive?

December 17, 2013 12:53 PM

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Buyers in the market for a new car may come across two or more vehicle options that appear to describe the same function. This is often the case when looking at vehicles offering both 4-wheel-drive (4WD) and all-wheel-drive (AWD) systems. While the two systems operate similarly, providing power to all four of the vehicle's wheels for increased traction, there are a few vital differences.

All-wheel drive is a power system that provides driving force to all four wheels of the vehicle, most often using all of the wheels to create forward or backward motion for the vehicle. Unlike 4-wheel-drive systems, which require that the driver engage 4WD and be given a choice of both high and low gearing ranges when increased traction is needed, an all-wheel drive vehicle keeps all four wheels in the hunt for traction continuously or automatically when needed -- depending on the system -- with no low-range option.

The increase in drive power provided by an all-wheel-drive system allows vehicles containing the system to work as all-weather vehicles. However, the presence of the system does not necessarily increase the off-road capability of a vehicle. For all-wheel driving with off-roading ability, a buyer must look specifically for a true 4-wheel-drive vehicle.

All-weather operation is the primary advantage of an all-wheel-drive system over the typical 2-wheel drive used for most car models. The increased usage will come at a price, however, as the all-weather vehicle can cost more than the equivalent 2-wheel-drive models.

With a 2-wheel-drive vehicle, the engine only powers two of the wheels on the car. The rest of the vehicle's wheels are for stability, rolling freely along the road. This is sufficient for normal use over paved roads. Should the road turn slippery due to water or ice, the two wheels may not provide enough traction to maintain complete control of the vehicle. If the two powered wheels fail to grip the road, the vehicle may skid out of control, with all of the wheels simply sliding along the road's surface.

With all-wheel drive, a skid due to water or ice can often be avoided due to having twice the number of wheels on the road receiving power from the engine and trying to find grip. To work properly, though, it helps to have all of the wheels in constant contact with the road's surface, which is where the car suspension comes into play.

The car's suspension system is designed to keep all four wheels on the road, regardless of the road's condition. It's made to allow for slight independent changes in the level of each wheel so that bumps or small holes in the road won't leave an all-wheel-drive vehicle operating on fewer than four wheels.

Whether or not to get all-wheel drive is just one of the choices you may need to make when purchasing a new car. With four wheels powering vehicle movement, it's helpful for regions that experience heavy rainfall or icy winters. The price will be a bit higher than for a 2-wheel-drive model, but for those looking to keep a vehicle on the road regardless of weather conditions, the expense may be more than worth the convenience of all-weather operation.

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