MEDIUM-DUTY OFF-ROAD CAPABILITY
The engineers who designed the MDX tested a range of competitive SUVs to help quantify off-pavement use patterns, customer needs, and engineering targets for the MDX. Accommodating extreme off-road use can impose compromises elsewhere in the vehicle, such as added weight, awkward entry and egress, poor fuel economy, and reduced on-road performance. With this in mind, the MDX team visited nine off-road parks in California, Nevada, Kentucky, North Carolina, and Michigan to study SUVs in their natural, off-road habitat. While a few competitors offer the extra ground clearance, driveline equipment, and chassis hardware necessary to support ambitious off road excursions, the engineers learned that few customers use these extreme capabilities regularly.
After observing casual off-roaders, MDX engineers concluded that surpassing the class's most capable off-road machine was not in MDX's best interests and that a medium-duty off-road capability was most consistent with the philosophy embraced by the MDX. Medium-duty capability would readily support trips into the wilderness for camping or to launch a boat without providing the rigorous equipment needed to conquer the extremes of the Rubicon Trail.
To define exactly what constitutes medium-duty off-road capability, the MDX engineering team selected 14 key performance criteria based on observations of casual off-road adventurers. They then constructed special test courses at their R&D facilities in North America to assure that MDX delivers all the intended capabilities with impeccable reliability and durability.
The list of test courses includes:
- 30-degree dirt hill
- Sand hill
- Water pit
- Rock roads
- Embedded log course
- Step-up, step-down
- Sand drag strip
- Gully course
- Ground contact course
- Washboard road
- Frame twister
- Power hop hill (23-degree slope with rippled surface)
- Gravel road
- Startable grade
Numerous engineering changes were based on experiences gained in testing. These included:
- A deeper oil pan was included to meet the hill climbing criteria.
- A more effective air filter was specified to remove dust from the engine's air supply.
- The tow hooks were upgraded to handle loads imposed during extraction from "stuck vehicle" situations.
- Waterproofing was added to support MDX's ability to traverse up to18-inch-deep bodies of water.
- Throttle actuation was calibrated to provide more sensitive control over engine output at low speeds.
For an acid test, engineers took prototype vehicles for a 200-mile off-road test on the Mojave Trail located in Southern California. This gauntlet of loose rocks, sandy washes, twisting grades, and narrow escarpments helped ensure that MDX has what it takes to venture off road and home again with confidence.
The results speak for themselves - MDX will climb a 31-degree (60-percent) paved slope with a two-passenger load. It has eight inches of ground clearance, a 28-degree approach angle, a 21-degree departure angle, and a 21-degree breakover angle for negotiating rough terrain. It can claw up a 28-degree (53-percent) dirt slope from a dead stop.
One of the reasons people buy SUVs is to be able to haul pop-up campers, medium-sized boats, and recreational vehicle trailers. To understand this facet of the MDX's makeup, MDX engineers polled focus groups and studied survey results that tapped 200,000 households. Their findings offered the insights needed to properly outfit the MDX to surpass the towing expectations of most customers.
Ultimately, the engineers concluded that a casual or weekend towing capability was most appropriate for MDX. Customer feedback helped set the towing limit at 4500 pounds for boats and 3500 pounds for other types of trailers. A heavier load is acceptable with boats because their pointed bow shapes impose less aerodynamic drag on the towing vehicle than a slab-faced, square-cornered trailer. The 3500/4500-pound rating is calculated to include up to four passengers and their cargo.
VARIABLE TORQUE MANAGEMENT' 4-WHEEL DRIVE
The MDX is equipped with an advanced 4-wheel drive system - VTM-4. The VTM-4 system consists of a pair of computer controlled wet clutches in the rear axle that work to maintain traction in all types of conditions.
Unlike other on-demand 4-wheel drive systems, MDX doesn't wait for slippage to occur before going to work. Instead, torque is proactively delivered to the rear wheels in proportion to forward acceleration to supplement front-wheel drive. This innovative, proactive approach pays two dividends: on dry pavement, there's less likelihood of torque steer (a tendency for propulsion forces to tug at the steering and nudge the vehicle off line) and there is more front tire adhesion available for cornering. In snow or wet conditions, automatic and proactive all-wheel drive gets the vehicle moving from a standstill with less chance of wheelspin.
If conditions are really slippery and wheel spin is unavoidable, VTM-4 instantly reacts by adding rear-wheel torque in proportion to both the slippage and the rate of increase of slippage. This enhances performance on low traction surfaces and also improves steering trace and feel during acceleration. In addition, the new VSA system further enhances traction in different conditions by providing a limited-slip differential effect for the front wheels. For 2003, the front-to-rear torque distribution has been remapped to provide up to a 30 percent increase in rear torque.
A special lock mode is also provided to help extract the vehicle from a stuck condition. To use this get-out-of-a-snowbank capability, the driver moves the shift lever to first, second or reverse and presses the VTM-4 lock button on the dash. With the lock mode engaged, VTM-4 "locks" the rear axle to provide maximum power transfer to each rear wheel. As speed increases above six mph, the system automatically reduces the lock effect to the rear axle. By 18 mph, the system reverts to normal mode.
DEFEAT WINTER OBJECTIVE
While studying competitive vehicles and the SUV marketplace, the MDX development team discovered that a well-designed product could be an effective defense against some of the frustrating rituals of the coldest months of the year. Based on that insight, members of the MDX development team that had grown up in northern parts of the U.S. drew on their personal backgrounds to formulate a clever "defeat winter" objective for MDX - consisting of a long list of designed-in features and systems designed to provide superior cold-weather performance. The result is that MDX can be a major confidence builder for those faced with driving through severe winter road conditions.
The MDX's winter-beating tactics begin with a chassis engineered for excellent dynamics on wet, icy, or snowy pavement, the VTM-4 all-wheel-drive system and, new for 2003, the application of vehicle stability assist (VSA). Various other chassis details are also engineered with a priority on winter driving. MDX's Goodyear and Michelin tires are compounded with silica to enhance ice and snow traction at cold temperatures. Testing has demonstrated that the grip of these tires is superior to many of the snow tires currently on the market. MDX's front suspension has a very low scrub radius so that braking on split-friction surfaces (such as when one side of the vehicle is on ice and the other side is on dry pavement) does not tend to pull the vehicle in one direction or the other.
Total roll stiffness is equitably distributed so that cornering response is linear and predictable even at low lateral Gs experienced during slippery conditions. The driveline is designed to provide natural and neutral handling response on snow and ice. With a static ground clearance of 8 inches, MDX is unlikely to get mired in deep snow drifts. The Anti-lock Braking System (ABS) is equipped with electronic brake-force distribution and four channels to provide maximum steering control even when traction varies dramatically from wheel to wheel. To preserve lateral stability, the rear brakes are programmed with a select-low strategy to modulate line pressure at both rear wheels as soon as either one approaches lock-up.
Features and amenities included as MDX standard equipment further enhance its winter-driving prowess. The rear heater is electronically linked to the operation of the front heater to speed warm up after a cold start and heat is ducted to all seating positions.
Electrically heated front seats and window defoggers are standard. For 2003, rear splash guards are provided to deflect slush and stones away from the side of the vehicle. Extra seals positioned at the bottom of the doors keep mud and slush from building up on lower surfaces that are likely to contact long coats, pant legs or dresses. Likewise the windshield molding and the outside rearview mirror mounting trim are shaped to guide moisture flow away from the side windows for optimum foul-weather visibility. Door-mounted rearview mirrors are electrically heated to clear frost and fog.
New for 2003, MDX models equipped with the Touring Package receive rain-sensing windshield wipers that, when in automatic mode, adjust wiper speed to correspond to the amount of rain that is contacting the windshield. The windshield washer reservoir is a large 1.2 gallons for a generous supply of washer fluid, and an indicator light advises the driver when it's time to replenish that fluid. Washer nozzles are engineered for optimum performance with a fluidic design in front and a jet-type sprayer in back. Since remote keyless entry is standard equipment on MDX, owners will not be kept from entering their vehicle by a frozen lock cylinder.