Honda Car Forum

CHASSIS OVERVIEW

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.

CHASSIS CONCEPT

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.

TIRES

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.

WHEELS

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

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.