2WD Vs. 4WD SUV
In recent years four-wheel drive has become a feature on many new SUVs. Four-wheel drive systems are no longer the exclusive domain of off-road capable or special use vehicles. Instead they are available to drivers who must drive in extreme weather or prefer the performance of four-wheel drive. However, two-wheel drive systems have their own advantages.
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Rear-Wheel Drive
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Many SUVs, especially those based on existing trucks, employ a front engine/rear-wheel drive configuration. In these SUVs the engine is mounted parallel to the body of the vehicle in what is known as a longitudal position. The engine's power is transferred to the rear wheels via the driveshaft, which runs the length of the SUV. By using the rear wheels as drive wheels, the front wheels are used only for steering and perform more responsively than if they were also drive wheels.
Front-Wheel Drive
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Front-wheel drive is more common on some smaller SUVs or crossover utility vehicles. In these vehicles, the engine is mounted perpendicular, or transverse, to the body of the SUV. It powers the front wheels directly beneath it, which are also used for steering. This means that the rear wheels need not be linked to the drivetrain and are essentially there just to stabilize the vehicle. Front-wheel drive configurations also place the engine's weight over the drive wheels, forcing them into more solid contact with the road surface.
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Four-Wheel Drive
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Four-wheel drive SUVs are usually similar to rear-wheel drive models, using a driveshaft to transfer power to the rear wheels while also powering the front wheels through direct mechanical linkage. This means that all four wheels are used to propel the vehicle, and even if one or two wheels lose traction, the remaining drive wheels will be able to keep the SUV moving until traction can be regained.
Four-wheel drive usually refers to SUVs that can operate in two-wheel drive mode (rear-wheel drive) or all-wheel drive. A shifter lever or electronic control on the dash is used to select between the two drive modes. All-wheel drive is the term used for vehicles that are always powered by all four wheels.
Advantages of Four-Wheel Drive
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The biggest advantage of four-wheel drive is increased traction. On slippery surfaces such as mud, snow, or ice, having four-wheel drive largely eliminates the potential of being stuck since all four wheels must be immobilized. Four-wheel drive is also useful for off-road driving where the trail surface may not be even and it becomes possible for some wheels to remain in contact with the surface while others are suspended over gaps and can provide no traction. For this reason, four-wheel drive SUVs intended for off-road use also feature heavy-duty suspensions and a higher ground clearance.
Advantages of Two-Wheel Drive
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Two-wheel drive systems are still preferable on some SUVs, especially those that are not intended for off-road use. Two-wheel drive systems are less expensive to design and manufacture than four-wheel drive systems, and SUVs available with all-wheel drive are often priced several thousand dollars above their two-wheel drive counterparts. Two-wheel drive SUVs also achieve better gas mileage due to the decreased weight of a simpler two-wheel drive system and the need only to provide power to two wheels at any given time.
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- Photo Credit Christopher Ziemnowicz/commons.wikimedia.org/wiki/File:Jeep_Grand_Wagoneer_snow_blade_side.jpg
