INTRODUCTION
The Acura MDX was the first product in what has proven to be a very popular portion of the market: a car-like, family-sized, luxury SUV. To venture beyond current competitive offerings with a no-compromise design, a new chassis was essential. Engineered to deliver the exhilarating driving experience and the outstanding vehicle dynamics expected of Acura products, MDX exceeds conventional SUV chassis design standards by a wide margin.
To provide the MDX with a smooth, refined, car-like ride, the MDX's suspension utilizes the following key design elements to meet its ambitious driving dynamics goals:
- Extra-wide track dimensions
- Short wheelbase for agility
- Rubber-isolated front and rear subframes
- Independent front and rear suspension systems with car-like geometry and long wheel travel for sporty handling and a comfortable ride
- Redesigned 17-inch cast-aluminum flangeless wheels (Touring Package)
- All-season, radial tires with silica tread compound for excellent traction and fuel Economy
- A Vehicle Stability Assist (VSA) system to integrate traction control, the VTM-4 system, Anti-lock braking, throttle control and stability control
- Four-wheel disc brakes with four-channel ABS and electronic brake distribution
- Torque sensing rack-and-pinion power steering
POWER RACK-AND-PINION STEERING
MDX's steering system is tuned for quick, linear, car-like response and sensitive feel - and the torque sensing, power steering assist is high for parking maneuvers and low at highway speeds. As cornering forces rise, understeer is mild and linearly progressive to accentuate predictability.
This system has been tuned for optimal steering feel. The valve body incorporates a damper valve that improves steering feel at high speeds, and a kickback reduction valve that substantially reduces steering kickback when encountering bumps or objects in the road or trail. A roller bearing in the steering shaft makes steering easier in parking situations.
FRONT SUSPENSION
The front suspension provides an incredibly smooth ride without compromising the MDX's nimble handling. The shock absorber units feature NWS (New Wide Setting) damper valves, which are designed to reduce low speed compression damping 10 percent and rebound damping by 30 percent while increasing high speed damping by 30 percent.
MDX has a wide track - 66.3-inches front, 66.5-inches rear - to optimize handling precision, stability, and ride comfort. The strut-type front suspension provides a generous 7.3 inches of wheel travel (4.3-inches in compression, 3.0-inches in rebound) with a moderate spring rate and relatively firm damping. Separate load paths to the unit body are provided for the coil spring and the shock absorber to facilitate tuning out road noise. A solid 0.9-inch stabilizer bar is linked directly to the strut via ball-joint connections to resist body roll during cornering maneuvers. The small 0.04-inch scrub radius designed into the front suspension is unusual for SUVs but this feature gives the MDX car-like steering response and handling that's consistent and predictable in on- and off-road situations. Accelerating or hard braking with uneven traction underfoot does not cause MDX to drift off line as is the case with many SUVs.
A low roll center (6.2-inches above the ground) further improves MDX's handling precision. The lower control arm bushings are designed to provide a stabilizing toe-out steering effect when loaded during braking or cornering. The L-shaped arm allows a very tight steering lock for good low-speed maneuverability. In fact, the Acura MDX's turn-circle diameter is a modest 37.2 feet.
FRONT SUBFRAME AND MOUNTING SYSTEMS
The MDX's engine, transaxle, transfer case, steering gear, and front suspension are all supported by a welded-steel subframe secured to the unit body's longitudinal rails through four tuned rubber isolation mounts. The front of the subframe assembly is tubular for maximum stiffness with minimal weight. A stiffener located under each subframe attachment fastener helps stabilize the assembly, thereby sharpening handling and braking performance. A stiffener plate bolted across the subframe under the transfer case greatly increases the assembly's rigidity. Two dynamic dampers and one mass damper are positioned to counteract noise and vibration, while two fluid-filled engine mounts quell vibration at idle and isolate powertrain NVH from the passenger compartment. The steering gear mounts are made of heat-resistant rubber to provide good vibration isolation, the firm retention necessary for sensitive on-center-steering feel, and life-of-the-vehicle durability.
REAR SUSPENSION
Like the front suspension, the rear suspension has also been tuned for a smooth, refined ride for each passenger position. The rear spring rate and damping were configured to reduce low speed compression damping and rebound damping while increasing high speed compression and rebound damping. To ensure more precise damping control throughout the entire range of the suspension system, the twin-tube, gas filled hydraulic shocks also feature New Wide Setting (NWS) damper valves.
The MDX's rear suspension is a compact, multi-link trailing arm layout for excellent ride and handling, light weight, and optimum packaging. Wheel travel is a generous 4.9 inches in compression and 3.3-inches in rebound. The three links that position each rear wheel laterally run between the knuckle assembly and the subframe. A trailing arm also runs from the unit body to each rear knuckle. Coil springs sit on the lowermost lateral link and anchor against the unit body directly behind each axle shaft. Shock absorbers, positioned ahead of the drive shafts, run from a low point on each knuckle to a secure attachment point on the unit body. Knuckles are an "in-wheel" design to optimize suspension geometry and packaging efficiency. Bushing compliance provides a modest toe-in effect in response to substantial cornering and braking loads to enhance dynamic stability. A solid 0.8-inch anti-roll bar helps keep the body relatively flat during hard cornering. The rear roll center is positioned at a 6.7-inch height to provide linear and predictable behavior at the limit of adhesion. The results speak for themselves, as MDX truly sets the standard for ride and handling in the luxury SUV category.
REAR SUBFRAME
Packaging of major components at the rear of the MDX is a major engineering challenge. The rear subframe, which supports most of the rear suspension and the rear axle drive unit, is made of high-strength steel for high stiffness and minimal weight. A rear subframe stay helps maintain precise positioning of the rear suspension and provides improved handling precision. The shape of the rear subframe is very important since it must accommodate the drivetrain components for the VTM-4 four-wheel drive system and the multi-link rear suspension pieces while still enabling the versatility of the third-row seat and flat cargo floor. For excellent ride and handling characteristics, the subframe attaches to the unit body at four widely spaced, rubber-isolated mounting points. Rear-suspension components, especially the springs and shock absorbers, are as compact as possible to facilitate a wide, flat load floor and to leave room for both a spare tire and a full-size fuel tank. The rear axle drive unit is mounted to the subframe by means of rubber isolators to block road and powertrain noise and vibration from the passenger compartment. A tuned dynamic damper attached to the drive unit cancels propeller-shaft and drive-shaft vibration.
WHEELS AND TIRES
For 2004, new die-cast flangeless aluminum wheels are fitted to the MDX and the MDX with Touring Package. Both have 6.5-inch-wide by 17-inch diameter rims, a 45mm offset dimension, and a five-lug bolt pattern. The new flangeless wheels provide a flush, integrated look. Large openings in the wheels provide ample brake-system ventilation. Tires supplied by Michelin and Goodyear are both sized P235/65R-17 and carry an M+S (mud and snow) label and a T (118 mph) speed rating. Both the tread and the internal construction were designed with computer-aided tools to achieve excellent ride comfort, low noise and wear, and best-in-class all-weather performance. Tread materials are compounded for excellent winter traction and low rolling resistance. During initial cold weather engineering tests, the MDX's tires consistently outperformed some of the most highly rated snow tires on the market.
The compact spare tire is carried under the load floor near the center of the vehicle and can be lowered by turning a hidden hex-head bolt with the provided lug-nut wrench. The hex-head bolt is located under a cover conveniently located in the rear hatch trim area. This arrangement guarantees the security of the spare and keeps it readily accessible while allowing enough space for the revised exhaust system. This configuration also allows access to the spare tire without disturbing luggage or cargo carried onboard. Room is provided to stow a flat or a full-size spare in the compact spare's location. Corrosion and failure of spare tire retention equipment, a common problem in some competitor SUVs, is avoided by use of stainless steel and polymer materials eliminating high-mileage failure.