2008 Acura TL - Chassis
The TL's front-wheel drive chassis provides significant benefits in a 5-passenger sedan. The drivetrain is more compact, overall package is lighter than if it were rear drive, and there is more passenger room. There are also important benefits in fuel efficiency.
With the introduction of the TL Type-S, the TL chassis now finds itself with multiple challengers. Also, whereas the TL's previous target was the BMW 530i Sport (a magazine comparison favorite), the 2008 TL lineup gives buyers the choice between two distinct models.
The TL is targeted toward buyers interested in a high-tech luxury sedan with excellent handling and chassis dynamics, but who also value a comfortable ride more than razor's-edge handling. The Type-S is aimed at buyers who want an increase in handling, braking and dynamic capability, but without a major sacrifice in ride comfort or interior noise.
With two separate TL models for 2008, chassis engineers were able to uniquely tune the suspensions for the different models' roles. The TL's wide tire contact patches enhance braking and handling with the standard all-season tires. High-performance "summer" tires are available on the Type-S that enhance acceleration, handling, and braking capability on both dry and wet surfaces. As a result both the TL and Type-S have excellent dynamic properties. Both feel crisp and taut, corner flat, and offer a high level of grip-even with four passengers aboard.
Noteworthy TL chassis enhancements include:
- Suspension tuning to enhance ride comfort while maintaining handling performance
- Shock absorbers and compliance bushing tuned for improved ride comfort
- Thicker hollow front stabilizer bar and new larger diameter hollow rear stabilizer bar to maintain handling precision
- New rear subframe bushings for reduced NVH
- Stiffer 17x8-inch aluminum-alloy wheels that result in less road noise
- Underbody airflow brake strake to improve cooling to reduce brake fade
Features exclusive to the TL Type-S include:
- Increased damping rates for superior handling
- Rear coil spring rate increased
- Solid front anti-roll bar and thicker rear anti-roll bar
- Damper mount stiffness increased 400-percent for enhanced response and feel
- Exclusive master cylinder for enhanced brake feel
- Brembo 4-piston front brake calipers
- Available 235/45R17 Bridgestone Potenza RE 030 high-performance "summer" tires on automatic and manual transmission models
HYDROFORMED ALUMINUM-ALLOY SUBFRAME
The 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. As water pressure increases, the aluminum tube bent to the exact shape of the die-a process that is more accurate and consistent than if done using a traditional forging process. 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.
The TL and TL Type-S are equipped with a pair of special fluid-filled Electronic Control Mounts. Connected to the hydroformed aluminum-alloy subframe, the mounts reduce vibration when the engine is idling.
The TL engine also has a side mount that helps control lateral movement. With the Type-S with 6-speed manual transmission, a special damper further reduces engine-rocking motion when the driver lets out the clutch or shifts gears.
The TL front suspension is a double-wishbone design 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 road holding, ride quality and packaging for the TL. The system uses coil-over shock absorbers that, unlike strut suspensions, are not stressed members of the suspension. This design reduces suspension friction and improves responsiveness to bumps. Suspension camber gain is maximized through the use of a shorter upper arm, while steering feel is enhanced through a high placement of the lower arm.
The upper suspension arm is extremely rigid, which makes it less likely to transmit vibrations from road surface irregularities into the cabin as road noise. A special compliance bushing on the lower arm better absorbs bumps and improves ride quality. A steel bar connects the shock towers to help deter deflection. Hollow, high-strength and lightweight, it enhances chassis solidity, steering precision and feel.
While the major geometry design elements are shared between the TL and TL Type-S, the tuning of these components results in cars with significantly different steering and ride feel.
The TL's suspension has been tuned with an emphasis on ride comfort while maintaining excellent handling. Thus, the hollow front stabilizer bar is 27.2 mm. Also, the front spring rate has been reduced by 7-percent. The front compliance bushing and dampers are re-tuned for ride comfort, without increased roll and only a slight decrease in performance during instrumented handling tests.
The Type-S suspension is re-tuned for significant performance gains. The hollow front stabilizer bar is replaced with a 27 mm solid bar. Although smaller in diameter than used with the previous TL, the new stabilizer bar is significantly stiffer than the hollow 27.2 mm bar it replaces. Additionally, the front damping rate has increased significantly. The dampers on the Type-S have been tuned specifically for the vehicle's goal of more aggressive handling. The result is increased road holding and enhanced stability with a reduced roll angle-all with a minimal loss in ride comfort. Also, the damper mounts are 400-percent stiffer, improving steering response and handling without compromising road noise isolation.
The TL rear suspension is a 5-link independent design with struts and coil springs. The suspension mounts to a steel subframe to improve road isolation and to 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 precision 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.
As on the front suspension, the rear suspensions are specially tuned on both the TL and TL Type-S. The TL has unique shock valving for improved ride comfort. The rear stabilizer bar design is a hollow 18.3 mm bar that reduces weight without sacrificing roll stiffness.
TL Type-S suspension settings are tuned for performance. Although the automatic and manual transmission TL Type-S models have the same suspension settings, the rear spring rate is increased 33-percent on vehicles equipped with a manual transmission, 14-percent on vehicles mated with an automatic transmission. The TL Type-S' solid rear stabilizer bar is 20 mm on cars with an automatic transmission. This results in greater roll stiffness in the rear, allowing for better handling balance and control.
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: lighter steering effort at low speeds with a heavier feel at higher speeds.
The TL Type-S has a power steering pump and steering gearbox designed to improve steering effort build-up and feel. To this end, the power steering pump has been tuned for decreased flow at 3250 rpm for increased effort build up. Additionally, the steering gearbox tuning increases effort by 15-percent at high speeds for better on-center feel. The steering rack has also been retuned for better damping feel. To keep up with the demands of spirited driving, the TL Type-S also features a new aluminum power steering fluid cooler.
Hydraulic dampers built into the steering system further improve stability during cornering and at high speeds. A one-way kickback valve decreases steering wheel kickback that can be caused by road irregularities. The hydraulic valve closes when it senses road irregularities, impeding disturbances to the steering wheel.
Stiffness of the steering gearbox mounting and the rear subframe also maximizes steering linearity.
Both the TL and TL Type-S feature as standard equipment 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®) with Traction Control System (TCS).
On the TL, the front brakes use 11.8-inch diameter (300 mm) ventilated cast-iron rotors clamped by single-piston brake calipers. Fade resistance has been improved with a larger brake strake in the front fascia, which directs more air to the brakes for improved cooling. This reduces brake temperature in high-demand braking, and helps improve the TL's brake fade resistance. The rear brakes employ 11.1-inch diameter (282 mm) solid rotors, gripped by single-piston brake calipers.
Both manual and automatic transmission TL Type-S models include a special Brembo brake package that includes 12.2-inch (310 mm) diameter ventilated front rotors clamped by 4-piston brake calipers. On the rear, the Type-S makes use of 11.1-inch (282 mm) diameter solid rotors mated with Brembo single-piston brake calipers. The calipers have an aggressive pad material to offer improved brake feel and to reduce fade in hard, repeated brake applications. The Brembo calipers are also 30-percent lighter than the standard calipers, reducing unsprung weight by 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. Rear brake rotors are the same 11.1-inch solid discs as used on the TL, but the calipers are given a black finish to match the look of the front brake calipers.
All TL models use a single 10-inch diameter vacuum booster assembly to reduce weight, increase stiffness, and to deliver more direct braking feel. Inside, the parking brake handle has been styled with a leather cover.
Electronic Brake Force Distribution
The TL features Electronic Brake Force Distribution (EBD), which automatically and continuously adjusts the pressure distribution between the front and rear brakes depending on how the vehicle is dynamically loaded.
Brake Assist comes standard on the TL. Its purpose is to help the driver apply full braking pressure in a "panic stop" situation. The system uses a microprocessor that continually analyzes and "learns" the driver's normal braking habits.
In an emergency braking situation when the brakes are suddenly applied and then partially released by the driver to avoid wheel lockup, brake assist helps the driver apply full braking force via the anti-lock actuator. A pressure sensor detects an increase in brake fluid pressure and activates the anti-lock braking system. Braking pressure is maintained momentarily after the driver's initial braking action unless the driver completely releases the brake pedal.
Anti-lock Braking System
Standard on the TL is a three-channel Anti-lock Braking System (ABS) that works in conjunction with the Vehicle Stability Assist™ (VSA®) system. Utilizing speed sensors located at each wheel, the system independently modulates braking power to the front rear wheels in tandem thus enhancing driver control during maximum-effort stops. A new ABS modulator improves response time and reduces noise when operating.
VEHICLE STABILITY ASSIST™ (VSA®)
The TL is equipped with 4-channel Vehicle Stability Assist™ (VSA®) that helps the driver retain control of the car in the event that the vehicle reaches its traction limits. For example, this may occur during aggressive cornering, encountering ice or dirt on the road, or entering a decreasing-radius corner too fast.
In the event of understeer, the system can apply the inside front and rear brakes to increase yaw, slowing the vehicle and enabling it to complete the turn. Engine power may be reduced by coordination of the Drive-by-Wire Throttle System™ and powertrain control module.
The 4-channel VSA® system controls all four brakes independently. In the event of oversteer (a condition where the rear tires lose grip), the system can apply 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 briskly 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-mounted switch is provided to disable the vehicle stability and traction control aspects of the system while retaining a fully functional ABS system.
The Acura TL has lightweight 17x8-inch aluminum-alloy wheels with distinctive designs for the TL and TL Type-S. The TL receives a split-five spoke wheel finished in Blade Silver, while the Type-S wheels are a 10-spoke design finished in Dark Euro Silver. Both wheels are lightweight designs, which contribute to quicker suspension movement and better ride quality by contributing to lowering unsprung weight. Optional 18-inch aluminum alloy wheels are available in three different finishes.
Bridgestone Turanza 17-inch all-season high-performance tires were specifically developed for the TL. The standard tire size is P235/45R17 M+S (all-season) which is available on TLs without the navigation system. TL's with navigation receive Michelin Pilot HX MXM4 all-season high-performance tires. All Type-S models are equipped with Michelin Pilot tires, and a high-performance 235/45R17 Bridgestone Potenza RE-030 "summer" tire is optionally available for the Type-S as well. The 2008 TL is also equipped with a tire pressure monitoring system.
The high-performance tires available on the Type-S further enhance dry/wet handling and braking, albeit at the cost of accelerated wear and overall traction performance in snow. In warm weather, the Potenza tires consistently out-perform all-season tires in slalom speed, maximum cornering g force, and braking distance.
A T135/80R16 temporary spare is used on the TL whereas the TL Type-S has a T145/70R17 temporary spare tire. The advantages of a temporary spare (versus a full-size spare tire) include improved trunk space as well as reduced vehicle weight for improved performance and fuel economy.
AVAILABLE TL SPORT SUSPENSION
Specifically made for TL models, an available dealer-installed sport suspension kit can be purchased, which includes all four specially-calibrated shock absorbers and springs, larger wheels and tires, plus unique aero components. Known as the A-SPEC kit, the parts provides firmer damping, increased spring rates, a lower ride height all with the goal of improved handling and to further distinguish the TL.
The A-SPEC kit includes:
- Pre-assembled performance springs and shocks that lower the vehicle 1.2-in.
- 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