Quick handling response, nimble performance, high dynamic capabilities, outstanding ride comfort and a fun-to-drive character aptly describe the 2008 Acura RL chassis. The RL features a highly rigid unit body that provides an excellent platform for the four-wheel independent suspension (independent front double-wishbone with independent multi-link rear). Aluminum suspension components front and rear cut unsprung weight to allow for more supple and responsive suspension action and more consistent traction and handling on rough roads. The optimized suspension geometry of the RL works with electronically controlled power steering, large wheels and tires and the Super Handling All-Wheel Drive™ (SH-AWD™) system to give the RL exceptional handling balance in virtually every driving condition. Ride quality and road noise isolation were also the focus of substantial engineering effort, so even with its elevated sporting performance, the RL remains quiet and composed.
The RL was designed to compete squarely with the best luxury sedans from Germany and Japan in dynamic performance interior luxury appointments, features and quality.
The new suspension works with the SH-AWD™ system to provide superb handling precision. The suspension's optimized geometry provides linear cornering feel, outstanding dry and wet weather cornering capabilities, a flat ride, and a high level of controllability at all times. It also results in an increased feeling of precision and security for the driver and passengers alike.
FRONT DOUBLE-WISHBONE SUSPENSION
The front suspension is a double-wishbone design with a large subframe mount and compliance bushing. In addition, the dampers feature rebound springs that reduce chassis attitude changes to ensure a flat ride during acceleration and cornering.
Specific performance goals for the RL suspension included better response over rough roads, improved steering feel, optimized geometry, and overall component toughness. The steering knuckle (or upright), upper arm, lower arm and subframe are all constructed of lightweight aluminum.
REAR MULTI-LINK SUSPENSION
The rear suspension is a multi-link design with a new enlarged subframe mount and a longer upper arm. As a result, the roll center is optimized for better turning response, improved cornering stability and more control in extreme conditions.
The optimized geometry results in more linear toe and camber changes during suspension travel. Improved roll stiffness also enhances the RL's cornering capabilities. The suspension also has anti-lift characteristics to reduce the pitching motion of the body during braking.
Harshness and road noise are also significantly reduced, and ride comfort is also measurably improved, thanks to these changes and a new compliance bushing.
In an effort for weight savings, lightweight aluminum is used in the construction of the control arms and subframe. The components are also stiffer to withstand the higher side loads that SH-AWD, larger tires and a stiffer unit body create.
ALUMINUM HYBRID SUBFRAMES
The RL front and rear aluminum subframes are composed of members made by high temperature bulge forming and high vacuum die casting. Both manufacturing techniques result in significantly lighter units than would be possible with either aluminum hydroform or steel hydroform processes.
To bulge-form these components, an aluminum tube is heated and pressurized
with air inside a specially shaped die. The ability to shape the component under
both heat and pressure means that less material can be used, lowering the overall
weight of the finished component.
The aluminum hybrid subframes on the RL save more than 40 lbs compared to comparable steel hydroformed subframes.
Buyers of premium sport luxury sedans expect the vehicle to deliver superior cornering precision while simultaneously delivering a pleasing ride. Since tires directly affect cornering loads, the RL is equipped with the largest tires ever offered on a production Acura sedan. Standard equipment are Michelin P245/50R17 98V high performance, all season tires that deliver outstanding cornering and are also M+S (Mud and Snow) rated. The tire's capability is further enhanced by the standard SH-AWD™ system (see Engine & Powertrain section for more information).
The RL spare tire is a temporary-use T155/70D17. A special dealer-installed 18-inch wheel and summer tire package is available for the RL. Models equipped with the optional RL Technology Package plus CMBS™ and PAX® Tires will feature P245-680R 480A 102V Michelin® PAX® run-flat tires mounted on unique aluminum wheels. A spare tire is included in the CMBS™/PAX® Package.
The RL wheels are 17x8-inch 5-spoke design constructed of cast aluminum alloy. The spare wheel is a 17x4T unit. Models equipped with the optional RL Technology Package plus CMBS™ and PAX® Tires will feature unique aluminum alloy wheels.
ELECTRONICALLY CONTROLLED, SPEED-SENSING, VARIABLE POWER ASSIST RACK-AND-PINION STEERING
Precise steering performance is an essential facet of the RL. The goals were to combine a light, yet linear steering feel at low speeds with a solid steering feel at high speeds. Together with the neutral handling characteristics of the chassis, the RL is engineered to feel like a smaller car to the driver than it actually is.
Compared to traditional mechanically controlled hydraulic power steering, the speed-sensing steering assist unit in the RL is controlled electronically. As a result, the steering assist provides a very linear and direct steering feel regardless of vehicle speed. In particular, the on-center feel is very precise and linear, with no discernible "dead spot."
VEHICLE STABILITY ASSISTTM WITH TRACTION CONTROL
Vehicle Stability Assist™ (VSA®) is standard equipment on the RL. It uses electronic traction control and ABS functions, combined with yaw and longitudinal/lateral acceleration sensors to quickly detect if the vehicle is about to understeer or oversteer. It then reduces engine output and applies one or more individual brakes to stabilize the vehicle—often before the driver is even aware of the instability.
4-WHEEL VENTILATED DISC BRAKES WITH ABS AND ELECTRONIC BRAKE DISTRIBUTION (EBD)
In keeping with the athletic capabilities of the RL, Acura designers upgraded the 4-wheel disc brakes to create a true high-performance system. They targeted the braking performance of top-level competitors from Audi, BMW and Mercedes-Benz as the benchmark to meet or exceed.
Up front, 12.6-inch diameter cast-iron ventilated front rotors team with 4-piston aluminum brake calipers. These multi-piston calipers are extremely rigid and are derived from racing applications. In back, 12.2-inch diameter cast-iron ventilated rotors, attached to their hub via lightweight aluminum collets, are gripped by one-piston aluminum calipers.
The RL includes Electronic Brake force Distribution (EBD) that automatically adjusts the front/rear brake pressure to suit conditions, while an anti-lock braking system (ABS) helps the driver retain directional control in hard braking situations. Also included is 4-channel Vehicle Stability Assist™ (VSA®).
Brake Assist helps drivers apply full braking pressure in an accident avoidance situation. To do so, a microprocessor continually analyzes and "learns" the driver's normal braking habits—monitoring both the rate of pressure applied and the total pressure that the driver normally applies to the brake system.
If the driver suddenly applies the brakes, Brake Assist brings the system to full ABS activation to help stop the vehicle in the shortest distance possible. It is only activated when the microprocessor detects that certain brake pedal speed and pressure thresholds are reached.
Importantly, Brake Assist helps the driver obtain full braking performance in an emergency. The Brake Assist system deactivates when the driver releases pressure on the brake pedal.
TIRE PRESSURE MONITORING SYSTEM (TPMS)
The onboard Tire Pressure Monitoring System (TPMS) with specific location and pressure indicators warns the driver when the air pressure raises/lowers in any tire. This helps reduce the chance of losing control of the vehicle due to improper tire pressure. Continually monitoring pressure levels is important because a slow leak (such as might be caused by a nail embedded through the tread) might not be detectable immediately, but over time would cause significant air loss leading to reduced tire grip and the potential of a blowout.
A sensor mounted on each wheel continually monitors tire pressure and sends a coded signal to an initiator located inboard of the tire on the chassis. The information is then sent to an electronic control unit that compares the values of each tire against an acceptable set of values.
When a tire's pressure drops significantly below the proper specification, a "CHECK TIRE PRESSURE" alert appears on the MID alert screen. The system can simultaneously display the specific air pressure in all four tires via the MID, making it simple to identify a low tire.
At the driver's preference the display can continually show the air pressure in all four tires. Regardless of whether the driver chooses to monitor the pressures, a warning will still occur if a tire drops below specification.