1998 Acura 3.2 and 2.5 TL -- Chassis
The 3.2TL and 2.5TL are both equipped with a 4-wheel all-independent double-wishbone suspension with coil springs and front and rear stabilizer bars. They also have four-wheel disc brakes, standard Anti-Lock Braking System (ABS) and a speed- sensitive variable power-assisted, rotary-valve, rack-and-pinion steering system.
While the two suspension systems are similar in concept, they differ in mechanical detail and calibration. Suspension tuning for the 3.2TL is biased toward a slightly softer, more luxurious ride, while the 2.5TL is tuned for a firmer, more sports-oriented ride. The goals for both, however, were to provide the automobile with linear responsiveness, excellent directional stability, good ride quality and excellent steering feel.
The suspension engineers were aided in these goals by the favorable 60/40 front/rear weight distribution, a weight bias that was determined to be the ideal for a front-wheel-drive car.
The front suspension comprises upper and lower control arms, a single-rate coil-over shock absorber mounted to the lower control arm, a radius rod and a tubular stabilizer bar. The front suspension was calibrated to minimize torque around the kingpin under cornering or bump reaction over a rough road, enhance straight-line stability by extending the caster trail, better resist crosswinds and minimize front-end dive under braking and rear-end squat under acceleration. Other priorities included reducing the tendency for the inside wheel to lift (jacking) under cornering by creating a very low roll center. On both models, the front roll center height is lower than at the rear, to enhance stability.
The 3.2TL uses an aluminum subframe to reduce weight while the 2.5TL uses a steel subframe to mount the suspension components. The bushings that locate the subframes to the chassis are specially designed to dampen vibrations transmitted into the passenger compartment and also to minimize flex and deflection in order to maintain proper suspension geometry. The 3.2TL front stabilizer bar has a diameter of 28.6mm with a 3.5mm wall thickness. The 2.5TL bar has the same diameter, but with a 4.0mm wall thickness. Both models also use hollow stabilizer bars to reduce weight.
The front shock absorbers are nitrogen gas-pressurized and fitted with a patented progressive-valve system. This valve uses special layered disk plates to control the fluid flow, rather than a fixed orifice. By using this type of valve, the suspension engineers were able to tune the damping force precisely to achieve a fine balance of handling and ride quality. In addition, a new upper shock mount was designed to minimize vibration.
The rear suspension features one upper and two lower control arms, a single-rate coil-over shock absorber mounted to the rear hub carrier, a trailing link to provide longitudinal location and to control, and a tubular stabilizer bar.
Like the front suspension, the rear suspension is located by a subframe. In this case, the subframe in both models is made of steel. The suspension was designed to minimize bump steer and unwanted toe change under cornering, improve the anti-squat response under acceleration, and provide stable, predictable handling during transient maneuvers.
On the 3.2TL, the rear subframe uses a special stiffening brace to increase camber rigidity and enhance stability.
Both models feature a liquid-filled bushing at the pivot point of the rear suspension trailing link to reduce noise and vibration. To increase stiffness and minimize suspension deflection, a steel sleeve is used to capture the bushing in the mounting point.
The 3.2TL stabilizer bar has a diameter of 14.7mm with a 2.6mm wall thickness. The 2.5TL bar has a diameter of 15.9mm with a 2.6mm wall thickness. Like the front shock absorber, the rear uses a progressive-valve system.
SPEED-SENSITIVE, VARIABLE POWER-ASSISTED, ROTARY-VALVE,
RACK-AND-PINION STEERING SYSTEM
Both TL models feature an innovative, power-assisted steering gear design that is lighter and more compact than conventional power steering systems. Instead of modulating power assistance to the steering rack solely in accordance with road speed, this system varies power assist by monitoring a combination of engine rpm, road speed and the amount of torque generated between the pavement and the tire. The advantage of this system is that it exercises more precise control over the amount of power assist provided. It also provides more linear steering with regard to lateral loads encountered while cornering, reduced kickback and a reduction in operating noise. A high-capacity power steering pump assures consistent operation under even the most aggressive maneuvers. The system is tuned to provide light, effortless steering during parking, yet provides excellent road feel at higher speeds. The steering ratio for the 3.2TL is 15.7:1 and 17.5:1 for the 2.5TL.
Braking is provided by a power-assisted, four-wheel disc braking system equipped with a dual-diaphragm master cylinder. The dual-diaphragm master cylinder is very compact, yet provides abundant boost for power assistance. Large, flex-resistant calipers help provide consistent braking performance. The front rotors are internally ventilated to aid in rapid heat dissipation. Front and rear rotor dimensions for both models are 282mm x 23mm and 260mm x 9mm, respectively. Swept area for both is 740cm2.
ANTI-LOCK BRAKING SYSTEM (ABS)
The standard Anti-Lock Braking System (ABS) features four wheel-speed sensors and three channels. The system exercises independent control over each of the front wheels and controls the rear wheels as a single unit. This is the latest generation ABS and features a number of refinements such as increased brake pedal stiffness, reduced pedal kickback when ABS is engaged, a 20% weight reduction in the ECU and wiring harness, and smaller overall size due to the integration of the modulator, accumulator and pump unit.
WHEELS AND TIRES
To reduce unsprung weight and enhance handling, both TL models are equipped with cast-aluminum alloy wheels. The 3.2TL wheels are 6.5 inches x 15 inches, while the 2.5TL's are 6.0 inches x 15 inches.
For excellent year-round driving performance, All Season tires are fitted to both the 3.2TL and 2.5TL. The tire specification for the 3.2TL is a Michelin P205/65 R15 94V M+S All Season, while the 2.5TL is equipped with Bridgestone P205/60 R15 91H M+S All Season tires.