4-Wheel-Drive and All-Wheel-Drive Systems -- Know Your Options

More and more often, 4-wheel drive and all-wheel drive are becoming popular options not only for SUVs, but cars as well. All SUVs and pickup trucks offer 4WD systems, and even some minivans like the Toyota Sienna and Pontiac Montana, offer available AWD systems. Oftentimes, more than one system is available for any given vehicle, leaving consumers puzzled.

With so many options to choose from, it's easy for drivers to get confused by a barrage of acronyms, each more meaningless than the last. For most consumers, there are three basic options: Full-time 4WD, part-time 4WD, or all-wheel drive. Although each system has its own merits, one thing is certain--any 4WD system will make your vehicle less fuel efficient and more complicated to repair and maintain.

On the other hand, with 4WD you are less likely to get stuck in snow or mud. Most consumers want 4WD because it adds a measure of security to a vehicle, but finding out and deciding which system is right for you is both an important and complex job. Choose wisely.

Part-time 4WD
This most basic system provides a choice of settings that can be changed depending on your driving situation, but cannot be left engaged on dry pavement. If it is, the transfer case will wear, resulting in mechanical damage. The settings range from 2WD, 4WD High, and 4WD Low. In vehicles that have part-time 4WD, each of the four wheels constantly gets 25% of the torque to prevent wheelspin when in the High or Low setting. In newer models, the driver can shift from 2WD to 4WD High while driving, but must come to a complete stop to shift into the 4WD Low setting. 4WD Low should only be engaged in extreme off-road situations. One drawback of part-time 4WD is that it must be continually engaged and then disengaged in conditions of light rain or snow. This type of system is best for people who really don't need 4WD, but occasionally go off-roading and want a little extra security when it snows.

Full-time 4WD
Unlike part-time 4WD, full-time 4WD, is just that--a system that can continually remain operating. This more advanced, convenient form of 4WD allows you to choose between all of the same settings, but can remain engaged while on dry pavement. Added to the High and Low settings is an automatic or full-time 4WD setting. As with part-time 4WD, the shift from High to Low must be made during a complete stop on most vehicles. Full-time 4WD is best for people who regularly drive in slippery conditions where constant shifting between 2WD and 4WD can become tedious.

All-Wheel Drive
All-wheel drive is similar to full-time 4WD in that the system is always sending power to the wheels with the most traction, but AWD has no 2WD switch. It is always operating in 4WD mode. When the road gets slippery, the AWD system locks the axles and automatically distributes power to all four of the tires. In many cases, AWD vehicles have no on/off switch. Some AWD systems are more rugged than others, though most can't be taken into extreme off-road situations. If the AWD system allows the driver to switch to a "low" range gearing setting, like in the Dodge Durango and Toyota 4Runner, then it is probably intended for severe off-road use. AWD systems work well in cars and crossover vehicles because they don't add much weight and make them true all-weather vehicles.

Safety Misconceptions
While 4WD and AWD may maximize traction better than 2WD, that doesn't necessarily translate into making it a safer vehicle. Oftentimes, drivers believe that because they can accelerate in snow just as quickly as on dry roads, they can do the same in terms of cornering and braking. On the contrary, 4WD and AWD do little to aid in cornering and nothing for braking ability on wet, snowy roads. Once moving, the physics of 2WD, 4WD, and AWD systems are pretty much the same. Rather than rely on AWD or 4WD, it's a better idea to think of them as an insurance policy that's there when you need it.

For most consumers, a set of quality all-season tires is a much better and less-expensive alternative to pricey and complex all-wheel-drive systems. Even the most advanced 4WD vehicle will be left spinning its wheels in the snow if they are shod with performance or touring tires.

Take a look at what kind of driving you normally do. Once you determine what type of vehicle best suits your needs, you can assess what type of system you need to get the job done. In some cases it may simply be 2WD with snow tires. In others, you may want to consider a more "robust" 4WD system with a low-range option. To help get a clear view off all your options, take a look at the following chart, sorted by vehicle class, that lists all the 2005 vehicles that offer AWD or 4WD systems.