4WD training with a 2WD sedan

Anyone who has watched several four-wheel-drive vehicles in a row negotiate a difficult section of trail has noticed that some seem to do so with ease, while others struggle. Frequently this is due to differences in the vehicles—suspension, ground clearance, lockers, etc.—but sometimes, counterintuitively, a bone-stock model of no particularly superior breed will make light work of a passage through which a modified über machine struggled.

The difference, of course is the driver. And what that driver is doing is optimizing the capabilities of the vehicle by picking the proper line through, around, or over obstacles in his path.

That skill of being able to recognize the proper line will benefit you more than all the traction aids on earth. And just what is The Proper Line? In one sentence, it is: A course that will, as far as is possible, keep all four of the vehicle’s wheels in contact with the surface (for optimum traction), while keeping all parts of the vehicle’s bodywork away from that surface (for reduced damage), and maintaining the vehicle’s stability (to avoid rolls, plunges off cliffs, etc.). Okay, that’s a sentence fragment, but you get the point.

 Bad line - tires in the low spots.

Bad line - tires in the low spots.

Even on easy trails, it’s worthwhile to train yourself to instinctively scan the terrain ahead and pick the optimum line. And some time ago I realized that the ideal vehicle for such training need not even be four-wheel-drive. The last two miles of the seven-mile dirt road to our little place in the desert has steadily degraded in the last few years, due to erosion from summer thunderstorms. As a result, the trip in and out is becoming more and more of a challenge for our old Mercedes 300D. Yet we’ve both been enjoying that challenge: easing it through ditches at just the right angle, straddling water-cut ravines that run straight down the road, judging the height of rocks on one bouldery downhill, and getting the speed just right on the final loose climb to the gate. You’re constantly reminded of axioms that serve well whether you’re working with five inches of ground clearance or twice that.

  • Straddling a water cut going uphill is usually safe, since they get narrower as you go. Beware doing the same thing downhill, when the cut is picking up micro-flows from the sides and getting wider. You might find yourself caught straddling a ditch too deep to cut across, and have to back up.
  • Precise wheel placement is a valuable skill. Know where your vehicle ends, and where each tire is going.
  • Keep your tires on the high spots.
  • Ditches perpendicular to the road are best crossed at an angle, one wheel at a time. Since the Merc has . . . modest . . . articulation and no traction aids, lifting a rear wheel is easy and will instantly cut traction. Sometimes a blip of the throttle is needed to coast across an air gap.
  • Loose, steep uphills with two-wheel (i.e. one-wheel) drive are a balancing act between ensuring sufficient initial momentum while avoiding excessive, rock-spewing speed. The perfect choice results in topping out at a walking pace with nary a spin of a tire. 
  • Closely spaced rocks can cause a feedback oscillation of the springs that cuts ground clearance drastically. Take them slow.
  • Finally, learn the undercarriage of your vehicle, and where the delicate bits are. Most cars have one side or the other that would be easier to damage—good to know if you have to drive over a rock.

Fortunately the W123 series Mercedes Benzes were built like Panzers to begin with, and ours seems to be handling its backroad duties with aplomb. Still, we occasionally muse on maybe a two-inch lift, an ARB locker, and some All-Terrains . . .