2004 Acura 3.5 RL -- Chassis

The 3.5 RL is equipped with 4-wheel, independent double-wishbone suspension with coil springs, 4-wheel disc brakes with ventilated front rotors, Anti-lock Braking System (ABS), and stabilizer bars at both front and rear.

Further, the RL features a state-of-the-art Vehicle Stability Assist (VSA) system that works in tandem with the ABS system and traction control to ensure the RL's smooth ride and stability in a wide range of driving conditions.

The RL's speed-sensitive, variable power-assisted, rack-and-pinion steering adjusts steering according to the driving situation, helps to ensure precise handling.

The RL's double-wishbone suspension layout is tuned to optimize handling quickness and stability without sacrificing ride quality. Optimized spring and damping rates, large front and rear stabilizer bars and firm front suspension bushings give the car a sporty feel. The front suspension uses unequal-length upper and lower control arms and a tubular stabilizer bar, while the rear suspension combines a longitudinal trailing arm, three lateral links and a tubular stabilizer. For excellent stability and improved ride quality, anti-squat and anti-dive geometries were built into the RL suspension.

To achieve a compliant ride without compromising handling response or cornering capability, the RL suspension also uses a number of innovations to reduce friction throughout suspension travel. The stabilizer bars use highly efficient ball joints at either end, as well as self-lubricating bushings at the sub-frame mounts. The upper arms of both the front and rear suspension have low-friction ball-joint bushings where they attach to the main structure, reducing overall friction while enhancing rigidity of the suspension assembly. Dampers have an advanced Progressive Valve design for increased damping control at low damper speeds while retaining quick, fluid response to large impacts. Special Teflon seals within all four damper units reduce friction even further for improved ride quality.

To give the RL a stable, predictable feel during hard cornering while improving overall lateral-acceleration capability, the suspension geometry was designed with a low roll center. The roll center is 59 mm above ground level for the front suspension and 70 mm above ground level for the rear suspension.

To reduce road noise and harshness, the bushing at the front of the rear-trailing arms is a liquid-filled design, instead of the more conventional rubber-damped bushing.

The standard, state-of-the-art Vehicle Stability Assist (VSA) system provides a heightened sense of stability in all driving conditions. Developed in cooperation with Bosch, this 4-channel system orchestrates the throttle and each of the RL's four disc brakes independently to seamlessly integrate traction control, Anti-lock braking, and stability enhancement processes under widely divergent road and driving conditions.

By monitoring input from vehicle sensors, the VSA can calculate a predicted range of vehicle response while constantly monitoring the vehicle's actual response and the driver's control inputs. If the actual response is outside of the predicted response range - as when cornering forces exceed tire performance, for example - VSA automatically takes corrective action. In the case of oversteer during hard cornering, VSA applies braking to the outside front or rear wheel to help counter the unintended yawing tendency. If understeer occurs, VSA applies braking to the inside front or rear wheel to help turn the RL back onto the intended course.

Unlike some vehicle stability systems, which can seem intrusive to enthusiast drivers, the Acura VSA is calibrated to add stability and predictability without stifling the driving enjoyment of the RL's carefully engineered chassis and double wishbone suspension. An indicator light flashes on the instrument panel while the system is actively stabilizing the vehicle. A cockpit switch is provided to disable the vehicle stability and traction control aspects of the system while leaving the ABS system fully functional.

The traction control aspect of the VSA system works just as seamlessly. When wheel slip is detected under acceleration, differential braking and engine controls modulate the amount of power put to the ground. In situations where the drive wheels are on surfaces with different friction properties, such as when one drive wheel is on wet pavement while the other is on dry pavement, the system applies pulsed braking action to the wheel that is slipping, allowing the tire with better grip to move the vehicle. In addition to taking independent control of the front wheel brake, the system can also reduce total engine power output to keep wheel spin in check.

Large, power-assisted, 4-wheel disc brakes are standard, with ventilated rotors in front for minimal fade and excellent heat dissipation. By fine-tuning the leverage ratio of the brake pedal and the response characteristics of the power-assist vacuum diaphragm, the RL engineering team achieved reduced stopping distances while making brake response more linear and intuitive. Combined with the "low-creep" torque converter, these refinements also help make it easier to hold the RL at a stop.

The 3.5 RL has a 4-wheel, 4-channel Anti-lock Braking System (ABS) that works independently of and in concert with the VSA system as needed. The ABS system operates in 3-channel mode during straight-line braking (apportioning braking power to the front wheels independently and the rear wheels in tandem), but automatically switches to 4-channel mode when the VSA system senses high cornering forces. This allows the ABS system to take advantage of weight transfer to the outside of the turn during cornering and apply higher brake pressure to the outer rear wheel for enhanced braking performance.

The ABS also enhances steering control during hard braking. Speed sensors at each wheel send signals to the ABS control module; if the system detects impending wheel lockup, it first holds, then reduces hydraulic pressure to the affected wheel, letting it regain traction before full braking resumes. The ABS function is also highly effective on split-friction surfaces, on which one side of the vehicle has significantly less traction than the other.

The speed-sensitive, variable power-assisted, rack-and-pinion steering uses a rotary valve that senses torque applied to the steering wheel and a vehicle speed sensor to vary power assist accordingly. The system adjusts steering assist for easy steering at low speeds and quick, precise steering at high speeds. The RL utilizes a cast-magnesium steering wheel for lighter steering feel, and a dynamic damper in the steering shaft for reduced wheel vibration.

The 2004 Acura 3.5 RL is equipped with P225/55R16 Michelin tires on 16-inch aluminum alloy wheels. The wide tires help provide outstanding all-season grip and performance, while maintaining exceptional ride characteristics and helping achieve optimal fuel mileage. The tires are an all-season design for enhanced traction on wet roads as well as on dry pavement.

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