The SUV Dilemma: 2WD? 4WD?

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So, you're finally going to buy an SUV. You've done all your homework, picked out the make and model, the engine size, even the color. Yet one decision still remains. Should you buy the 2WD or 4WD version?

Thousands of people will purchase an SUV this year yet most will never take it off road. If the primary purpose of your SUV is to haul the kids, take long highway trips and sit up nice and high, then a 2WD version will probably do just fine. And, except for the missing 4x4 badges, your friends will never know since most 2WD SUVs are almost indistinguishable from their 4WD counterparts.

The Scoop On 2WD

For most SUVs, the term 2WD is actually a misnomer. Base model 2WD vehicles are actually 1WD, a single wheel transferring power from the differential to the road. If you opt for a 2WD SUV, be sure the manufacturer offers the option of a limited slip rear differential. This system allows power to be transferred to either rear wheel. A 2WD SUV so equipped can handle dirt roads and gravel washes with complete confidence. There are also a number of SUVs whose 2WD power is delivered via the front wheels. This arrangement offers superior traction in either rain or snow.

A 2WD SUV is also lighter (no extra hardware to drive all four wheels) and therefore earns a slightly better EPA fuel mileage rating. Maintenance costs should be lower over the life of the vehicle, again fewer moving parts to worry about. Most importantly, depending on your age and gender, insurance costs are generally lower for a 2WD SUV.

Is 4WD For You?

Drivers who opt for 4WD have numerous variations from which to choose. One of the most commonly used 4WD systems employs a simple high/low transfer case which routes power equally to the front and rear differentials. When engaged, both front and rear wheels turn at the same rate of speed. This system is called part-time 4WD and is intended only for use off road. Because a vehicle's wheels rotate at different speeds when turning a corner, part- time 4WD cannot be engaged on dry pavement (which doesn't allow the wheels to slip) or at speeds greater than 40 mph (taking a curve at this speed will damage the gearbox).

A clever twist on part-time 4WD is called on-demand 4WD. The system operates in the 2WD mode but will automatically divert power to the other wheels if slippage is detected, thus temporarily engaging the 4WD until traction is regained. This system can be left on during normal driving conditions.

Next up is the full-time 4WD system. Full-time 4WD employs front, rear and center differentials that allow individual wheel speed to vary. SUVs so equipped can operate in the 4WD mode at all times and on any surface condition. When disengaged, full-time 4WD operates as normal 2WD. This system best serves those who occasionally require 4WD under normal driving situations, such as during heavy snows or when towing.

Manufacturers use many different names for their 4WD systems. To be sure you are looking at full-time 4WD, the transfer case must be equipped with some form of a center differential.

Finally we come to all-wheel drive (AWD). All-wheel drive means the system is permanently engaged at all times. Power is sent to any or all wheels, controlled by a series of electronic gears that detect wheel slippage. Vehicles like the Honda CR-V employe a very basic AWD system designed more to handle inclement weather and improve road stability. AWD on this class of vehicle is not intended for off road use. At the higher end of the spectrum, vehicles such as Land Rover's Range Rover offer AWD systems that are more sophisticated and can be used in all on and off road situations.

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