Buyers of premium sport luxury sedans expect them to deliver superior cornering precision. Since tires directly affect cornering loads, the RL is equipped with the largest tires ever offered on a production Acura sedan. Original equipment is a Michelin P245/50R17 98V high performance, all season tire that delivers outstanding cornering and is M+S (Mud and Snow) rated. This tire is 20mm wider (0.8 in.) wider, and an inch larger in wheel diameter, than the 225/50 R16 tire found on the 2004 model. The tire's capability is further enhanced by the standard SH-AWD system (see Engine & Powertrain section for more information).

An 18-inch accessory wheel and summer tire package will be available as a dealer-installed item. The RL spare tire is a temporary T155/70D17.

WHEELS

The RL wheels are 17 x 8J-inch cast aluminum alloy. They are an inch larger in diameter and one inch wider than the 16 x 7JJ-inch units found on the 2004 3.5 RL. The spare wheel is a 17 x 4T unit.

ELECTRONICALLY CONTROLLED, SPEED-SENSING, POWER ASSIST RACK-AND-PINION STEERING

Precise steering performance is an essential facet of the RL. The goals were to combine a light, but 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 than it actually is to the driver.

Compared to traditional mechanically controlled hydraulic power steering, the speed-sensing steering assist unit in the RL is controlled electronically. As a result, it 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."

VSA WITH TRACTION CONTROL

Vehicle Stability Assist (VSA®) is standard equipment on the RL. It uses electronic traction control and ABS functions, combined with a 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 and exceed.

New 12.6-inch cast-iron ventilated front rotors use aluminum 4-piston calipers. These multi-piston calipers are extremely rigid, and are derived from racing applications. In back, 12.2-inch cast-iron ventilated discs attach to their hub with lightweight aluminum collets and are gripped by one-piston aluminum calipers.

The 2005 RL includes Electronic Brake force Distribution (EBD), which 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 assists the driver in obtaining 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 location and pressure indicators warns the driver when the air pressure lowers in any tire. This helps reduce the chance of losing control of the vehicle due to low air pressure. This is important because a slow leak, such as might be caused by a nail embedded through the tread, might not be detectable immediately but would, in time, cause significant air loss, loss of grip and potentially 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 display the air pressure in all four tires simultaneously via the MID, making it simple to locate a low tire. If there is a fault in the system, a "CHECK TPMS SYSTEM" alert appears.

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.