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Do you really need four-wheel drive?

While four-wheel drive (4WD) is the king of rock crawling, mud bogging and all other sorts of off-road adventures, you don't have to scrap your reliable two-wheel drive (2WD) to join in the fun. By simply adding a few upgrades, you and your 2WD may be able to respond to the call of the wild.

Closing the gap
Ten or 15 years ago, the choice between 2WD or 4WD light trucks involved some serious thinking. Although tempered by the fact that the off-road models held their resale value in direct proportion to their less expensive 2WD counterparts, at least on a regional basis, the cost of 4WDs was higher. To further complicate matters, the 4WD option at that time came with some noticeable downsides: harsh rides on paved roads and heavier weight, resulting in reduced fuel economy and less highway horsepower.

With the growing popularity of light trucks in the forms of both pickups and SUVs, manufacturers realized that this vehicle category was being used in a broader range of driving conditions than before. This realization resulted in a wide truck selection that appeals to today's driver and a narrowing gap between two- and four-wheel-drive features.

Today, some of the larger heavy-duty trucks come with the same suspension systems loaded on their 2WD and 4WD models. The only real remaining differences are the inclusion of differentials on the front wheels of 4WDs and the availability of lower gearing and higher low-end torque in the 4WD mode – a plus for tow vehicles, regardless of whether or not they ever actually encounter off-road driving conditions.

Making modifications
So what sort of modifications will breathe new life into your trusty 2WD and open up new off-road capabilities? Look at the 2WD Toyota Prerunner, a phenomenon modeled after the 2WD trucks used to prerun desert races. While having to cover the same terrain as the actual race trucks, they are not obligated to do everything that the race trucks are capable of doing. You may also consider that the famed Paris-to-Dakar rally now has a category for 2WD vehicles.

The ability to take a 2WD off road boils down to satisfying two simple requirements: having sufficient ground clearance and getting traction. Lift kits – designed to provide that extra clearance for oversized tires and to avoid gutting your undercarriage on rocks while still maintaining steering and braking geometry – are available for 2WDs. By using lift kits and other suspension upgrades, you can now put a system together that is tailored to your own personal off-road requirements without having to compromise highway comfort.

The same holds true for tires that are intended to provide you with the traction you need. With the variety of off-road competitions, each requiring a specific tire design and tread, the only limitation is your wallet. BFGoodrich, with an unchallenged success rate for both Baja and Paris-to-Dakar rallies, markets a heavily treaded tire designed as the rear tire for 2WD desert racers.

One possible additional option for 2WD truck owners is an effective locking system for the differential. A number of 2WD and 4WD pickups have limited-slip differentials that lock up the axle when a wheel starts to slip. When the axle is locked, full power is delivered to both wheels.

Limited slip
If what you just read has left you scratching your head, here's an explanation of slipping and non-slipping differentials in simpler terms: When turning, the wheel on the inside of the turn is traveling a shorter distance than the wheel on the outside of the turn. The differential allows the two drive wheels to rotate at different speeds by sensing the amount of traction on each wheel. In the case of a turning vehicle, the inside wheel has more weight or traction, so the power goes to the unweighted wheel.

Now, consider what happens when those wheels get stuck in mud or loose sand. The wheel with the least amount of traction gets all of the power, but since it doesn't have a bite into the surface of the road, it simply spins in place.

Limited-slip or automatic locking differentials are usually sufficient in very light off-roading situations, but they are not a substitute for a manual locking system. With a manual locking system, you can lock up your differential at the base of a steep grade or right before you slog through mud or sand – or at any other time of your choice for that matter. While most manual locking systems are marketed to hardcore off-roaders, they can effectively pull a 2WD through 4WD-sized conditions about 95 percent of the time. If you're worried about that remaining 5 percent of time, then you really do need a seriously modified 4WD.

These modifications are not cheap and, with the exception of tires, they are a bit beyond the skill level of most shade tree mechanics. If you have to choose, however, between buying a new 4WD vehicle or adding upgrades to a trusty 2WD, the latter will add brawn to that 2WD at a fraction of the cost of a new 4WD.

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