HEADLINES

2005 Acura TL Chassis

OVERVIEW

In a 5-passenger sedan, the benefits of front-wheel drive include lighter and more compact engine and driveline packaging, enhanced fuel efficiency, and increased passenger spaciousness.

CHASSIS CONCEPT

From a handling standpoint, the TL chassis was designed to challenge the BMW 530i Sport, a magazine comparison favorite.

To accomplish this, engineers focused on creating a rigid platform with a performance-tuned suspension and large tires. The large tire contact patches improve braking and handling with all-season tires. Available high-performance tires boost acceleration, handling and braking capability even higher on both dry and wet surfaces.

The TL has excellent dynamic properties. It feels crisp and taut, corners flat and offers a high level of grip-even with four passengers aboard. In internal testing, both TL models (5-speed Sequential SportShift automatic transmission and 6-speed manual transmission) surpass the 2003 BMW 530i and the Lexus ES 300 in a 600-ft. slalom exercise and in maximum cornering capability.

Noteworthy chassis features include:

  • 17 x 8-inch aluminum-alloy wheels
  • P235/45R17 all-season Bridgestone Turanza tires
  • Double-wishbone front suspension
  • 5-link double wishbone rear suspension with pillow joint for precise control
  • Sport-tuned shock absorbers
  • Lightweight aluminum-alloy front subframe
  • Special transmission mounts for improved ride quality

Braking performance features:

  • 4-wheel disc brakes
  • 10-inch vacuum booster
  • Anti-lock braking system (ABS)
  • Electronic Brake Force Distribution (EBD)
  • Brake Assist
  • 4-channel Vehicle Stability Assist (VSA)

The TL with 6-speed manual transmission includes the following features:

  • Available 235/45R17 Bridgestone Potenza RE 030 high-performance tires
  • Brembo 4-piston front brake calipers
  • Rear engine rocking damper
  • 17-inch aluminum-alloy spare wheel

HYDROFORMED ALUMINUM-ALLOY SUBFRAME

To reduce mass and improve handling agility, the 2005 TL uses an all aluminum-alloy front subframe that carries the engine, transmission and lower suspension links.

The U-shaped subframe cradle is hydroformed. In this process, a single aluminum-alloy tube is inserted into an immensely strong die, which is locked closed before the tube is pressurized with water. The resulting component is lighter and stronger than a multi-piece component would be. The hydroformed cradle is then attached to aluminum-alloy corner brackets to form the complete subframe.

Compared to the traditional steel subframe on the 2003 TL, the aluminum-alloy TL subframe weighs 36 percent (about 23 pounds) less. Besides its lighter weight, the subframe has increased bending rigidity, which reduces noise experienced in the passenger cabin, particularly as the engine is starting.

ENGINE MOUNTS

The TL has a pair of special fluid-filled Electronic Control Mounts. Connected to the hydroformed aluminum-alloy subframe, they reduce vibration when the engine is idling. The transmission has its own proprietary mounts including a special lower mount designed specifically to increase ride comfort.
Besides the lower mounts, the TL engine also has a side mount that helps control lateral movement. And on the TL with 6-speed manual transmission, a special damper further reduces engine-rocking motion when the driver lets the clutch out or shifts.

FRONT SUSPENSION

The TL front suspension is a double-wishbone system with a rigid stamped steel upper arm and a steel lower arm. The system is functionally related to the systems used on Formula One and Indy Cars, and permits the best combination of roadholding, ride quality and packaging for the TL. The system uses coil-over shock absorbers that, unlike in strut suspension, are not stressed suspension members. This reduces suspension friction and improves responsiveness to bumps.

Suspension camber gain is maximized through the use of a short upper arm, while steering feel is enhanced through a high placement of the lower arm.

The upper suspension arm is extremely rigid to reduce the transmission of road noise into the cabin, while a special compliance bushing on the lower arm better absorbs bumps and improves ride quality. A steel bar connects the shock towers. Hollow, high-strength and lightweight, it enhances chassis solidity, steering precision and feel.

A hollow tubular steel stabilizer bar is specially tuned to the best balance between firm handling and luxurious ride comfort.

REAR SUSPENSION

The TL rear suspension is a 5-link independent system with struts, coil springs and anti-squat and anti-lift geometry. It mounts to a steel subframe to improve road isolation and a help provide a quiet interior. The rear suspension geometry adds "toe-in" when the suspension is compressed, improving handling stability over bumps and during hard cornering and braking.

A stabilizer bar further improves handling by limiting body roll, while a special "pillow joint" for the lateral links improves camber rigidity. Rubber shims on the leading and trailing arm bushings improve ride comfort.

STEERING

The TL uses torque-sensing, variable power-assisted rack and pinion steering. The engine-driven variable-output pump provides the kind of steering feel that driving enthusiasts like: modest steering effort at low speeds and precise feel at higher speeds. The steering feel is very linear and evenly weighted.

Hydraulic steering dampers built into the system further improve stability during cornering and at high speeds. A one-way kickback valve decreases kickback in the steering wheel that can be caused by road irregularities. The hydraulic valve closes when it senses road irregularities, impeding disturbances to the steering wheel.

Increasing the stiffness of the steering gearbox mounting and the rear sub frame also maximizes steering linearity.

BRAKES

The TL has 4-wheel disc brakes with Electronic Brake force Distribution (EBD), Brake Assist, an Anti-lock braking system (ABS) and 4-channel Vehicle Stability Assist (VSA) including traction control as standard equipment.

The front brakes are ventilated cast-iron discs with single-piston calipers. For better fade resistance, cooling air flows to the brakes through the front fender air duct ahead of the front wheels. This cooling airflow reduces the brake temperature by 84 F. in high-demand fade tests. The rear brakes are solid discs, gripped by single piston calipers.

Brembo rotors and aluminum-alloy front brake calipers are standard on the 6-speed manual transmission TL. The calipers have four pistons each, and more aggressive pad material, to offer improved brake feel and reduced fade in hard repeated brake applications. They are also 30 percent lighter than the standard calipers, saving 4.3 pounds per wheel, which in turn improves suspension response for better ride and handling. The calipers feature an attractive black painted finish with the Acura name.

A single 10-inch vacuum booster is used to reduce weight, increase stiffness and deliver more direct braking feel. In a departure from the previous TL, a hand parking brake is used instead of a foot brake. This applies to both automatic and manual transmission models.

Electronic Brake Force Distribution

An added feature for TL is Electronic Brake force Distribution, which continuously and automatically adjusts the pressure distribution between the front and rear brakes depending on how the vehicle is loaded.

Brake Assist

Brake Assist comes standard on the 2005 TL. Its purpose is to help the driver apply full braking pressure in an accident avoidance situation. To do so, a microprocessor continually analyzes and "learns" the driver's normal braking habits.

In an emergency braking situation when the brakes are suddenly applied bu inadvertently released by the driver to avoid wheel lockup and then reapplied, brake assist helps the driver apply full braking force via the ABS actuator. A pressure sensor detects an increase in brake fluid pressure and activates the ABS system. Braking pressure is maintained momentarily after the driver's initial braking action.

Anti-lock Braking System

Standard on the TL is a three-channel Anti-lock Braking System, which works in conjunction with VSA System. Utilizing speed sensors located at each wheel the system modulates braking power to the front wheels independently and to the rear wheels in tandem-enhancing driver control during maximum-effort stops.

VEHICLE STABILITY ASSIST (VSA)

The TL is equipped with 4-channel VSA that helps the driver retain control of the car in the event the vehicle reaches its dynamic traction limits, for example through aggressive cornering, encountering ice or dirt on the road, or entering a decreasing-radius corner too fast.

In the event of understeer (where the front tires lose grip), the system applies the inside front and rear brakes to increase yaw (vehicle "rotation"), slowing the vehicle and enabling it to complete the turn. Engine torque may also be reduced by coordination of the Drive-by-Wire Throttle System and Engine Controller.

The 4-channel system controls all four brakes independently. In the event of oversteer (where the rear tires lose grip), the system applies the outside front and rear brakes to decrease yaw, slowing the vehicle and enabling it to stay on its intended path.

An indicator light on the instrument panel alerts the driver whenever the VSA system is actively enhancing the vehicle's stability.

The traction control component of VSA uses sensors that monitor each of the wheels and a computer-controlled modulation of engine power and front brakes to help prevent wheel spin when starting out or accelerating. If the sensors detect wheel spin, traction control reduces engine power and applies brake force to the affected wheels. This helps the TL maintain traction during acceleration and helps the driver retain steering control, even when accelerating on slippery surfaces.

A cockpit switch is provided to disable the vehicle stability and traction control aspects of the system while leaving the ABS system fully functional.

WHEELS

The Acura TL has lightweight 17 x 8-inch aluminum-alloy wheels. Lighter wheels contribute to quicker suspension movement and better ride quality by contributing to lowering unsprung weight.

TIRES

Bridgestone 17-inch all-season high-performance tires were developed for the TL. The standard tire is P235/45R17 M+S (all-season), with 235/45R17 high-performance tires available for the TL with 6-speed manual transmission. Navigation system-equipped models without the optional high performance tires are shod with Michelin all-season tires.

The 17-inch tires significantly contribute to the TL design objectives including its aggressive, athletic appearance. They also measurably improve dry handling and braking.

Available high-performance tires further enhance dry handling, wet handling and braking, at the cost of performance in snow and accelerated wear. In warm weather these tires consistently outperform all-season tires in slalom speed, maximum cornering g force, and braking distance.

About 95 percent of US-market TL units have all-season tires (80 percent in Canada). The remaining five percent of TL purchasers (mostly in Sunbelt states) select high-performance tires.

The TL with manual transmission has a T145/70R17 temporary spare tire. A T135/80R16 temporary spare is used on the TL with automatic transmission. The advantages of a temporary spare include maximum trunk space, and reduced vehicle weight for better handling and fuel economy.

If a TL owner wishes to use chains to drive in difficult snow conditions the use of cable chains is recommended.

AVAILABLE SPORT SUSPENSION

An available sport suspension kit can be purchased, which includes all four shock absorbers and springs, larger wheels and tires plus aero components. Known as the "A-SPEC" kit, it provides firmer damping and spring rates for sportier handling. A lower ride height further distinguishes the sport suspension-equipped TL cosmetically.

The A-SPEC kit includes:

  • Pre-assembled performance springs and shocks that lower the vehicle approximately 1.2 in. (30 mm)
  • 18-inch wheels with 235/40ZR18 Yokohama AVS ES100 tires
  • Aero kit
  • Rear spoiler
  • Special steering wheel with distinctive shape and stitching
  • Performance brake pads (for automatic transmission vehicles only)
  • A-SPEC badging
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