Explorer: still head of the class

Automotive Design & Production,  Oct, 2005  by Christopher A. Sawyer

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Ford's 2006 Explorer is not a clean-sheet redesign of it best-selling mid-size SUV, but an extensive update of the previous model. Throwing out the work that made the previous vehicle the segment leader--a title the Explorer has held since its 1990 introduction--didn't make sense. However, the rapidly changing light-truck market meant a quick restyle and interior updating wouldn't last against a flood of competitors. Something more complete was necessary.

"When the Explorer was launched in 1990," says Judy Curran, chief engineer on the 2006 Explorer program, "the total SUV market was 929,000 units, or 6.5% of the vehicle market. By 2004, SUV sales accounted for 27.5% of the total market, the number of nameplates had risen from a few dozen to more than 200, and the market had fragmented into various sub-segments from what had been a traditional body-on-frame light truck segment." The crossover portion continues to grow at the expense of traditional SUVs like the Explorer, but Curran and her team reasoned the buyer for a traditional SUV--an on- and off-road vehicle with the ability to tow--shouldn't be sacrificed to chase that target. "Especially," she adds, "when our competition is busily adding new vehicles into this segment."

The casual observer can be forgiven for thinking there's little new about the 2006 Explorer other than the bumpers, lights, wheels, grilles, and interior. Granted, the doors, glass, roof and rear quarter panels are carried over--which gives the redesign a fresh-but-familiar look--but the revised front end hides a nearly 4-in. increase in overhang, and the body hides a new frame design, revised powertrain, upgraded brakes, and a redesigned independent rear suspension. "It's about as complete a redesign as you can do without starting from a clean sheet," claims Curran.

The Structure:

The fourth generation Explorer frame follows F-150 practice with its tube-through-tube design. Fully boxed main structural cross beams span the full width of the frame, exiting through holes cut into the main rails. A continuous weld is made along the perimeter of the hole, which ties the cross beam tightly to the main frame rail. Secondary cross beams are stamped sections welded to the inner edge of the main rails. The front rails extend nearly 4-in. farther forward than before, and contain crush initiators--precise voids cut into the frame rail along its inner and outer edges rather than pre-formed depressions--to manage crash forces. Directly behind this section, the frame rails head downward, and this S-shaped section contains a revised insert to minimize passenger compartment intrusion. Despite these changes, the frame does not look radically different from that of its predecessor, though Magna (Aurora, Ontario) now provides the frame to Ford in place of Tower Automotive (Novi, MI), and the sections are slightly taller and wider than before. The frame is, however, 63% stiffer in bending and 55% stiffer in torsion, and tested to the same off-road and towing standards set for the F-Series Super Duty.

As before, the rear half shafts pass through "portholes" in the frame rail in order to eliminate the frame kick-up and keep the vehicle's center of gravity low. The previous short/long arm independent rear suspension is replaced by a trailing arm design with three lateral links per side which, at first, appears to be a retrograde step. "Most car trailing arm suspensions have been replaced by multi-link or similar setups for better control over ride and handling," says Chris Brewer, chief chassis engineer on the 2006 Explorer, "but these designs are more costly, especially when they must be designed for worst-case, heavy-duty use cycles found with light trucks. By comparison, a trailing arm provides simpler location and attachment, can be made more robust, and is less expensive to produce." However, it also can add lift-throttle oversteer to the mix. The addition of lateral links to control wheel movement throughout the suspension's full travel eliminates this tendency.

[ILLUSTRATION OMITTED]

The Chassis:

The stamped steel front suspension is basically carried over, though the control arms are both stiffer and lighter. "The pieces are two times stiffer than before," says Brewer, "basically through a change in the gauge of the metal at non-critical points. Plus, we've been able to use bushings with a 25% to 30% softer recession rate to improve ride comfort." Brewer's team also ditched the previous gas-charged dual-tube dampers for a set of Tokico monotube shocks. "They have a larger piston, and we no longer have the problem of pushing the gas out of the oil that we had with the dual-tube design. This gives us better control over the damping rates and puts less heat in the shock in heavy use."

The brake discs are unchanged from the previous model, with 305 mm X 30 mm ventilated front and 301 mm X 12 mm solid rear discs. The twin-piston front calipers increased in size from 46 mm to 51 mm, and flex less under full brake pressure. Pad thickness has increased in proportion to the caliper size. Three-channel ABS with Electronic Brake force Distribution (EBD) is standard along with traction control and Ford's proprietary Roll Stability Control. Wheel and tire sizes have increased, with 17-in. wheels and tires standard. Eighteen-inch units are optional.