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Notes From The Road

2WD vs. 4WD - Do you really need four-wheel drive?
By Debbie Murphy/

Limited Slip
If what you just read has left you scratching your head with confusion, 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, the vehicle 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 4x2 through 4x4-sized conditions about 95 percent of the time. If you're worried about that remaining five percent of time, then you really do need a seriously modified 4x4.

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 4x4 vehicle, or adding upgrades to a trusty 4x2, the latter will add brawn to that 4x2 at a fraction of the cost of buying a new 4x4.

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