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2005 BUICK LaCROSSE: RIDE, HANDLING - AND 'QUIET TUNING'

Beneath the all-new styling of the 2005 Buick LaCrosse is an extensively re-engineered underbody aimed at enhancing overall ride and handling, while staying true to the Buick hallmarks of comfort and quietness.

Extensive refinements have been engineered into LaCrosse's overall structure and chassis. In fact, 80 percent of the suspension tuning is new, giving LaCrosse even more response and control, while providing a smooth and quiet ride.

"The overriding goal during LaCrosse's dynamic development was to maintain the smooth, quiet ride that has been a longstanding Buick tradition, yet provide a level of driver response that has become a key requirement in this market," said James E. Affholter Jr., vehicle system engineer for chassis.

At-a-glance changes on the 2005 Buick LaCrosse, compared with the Regal/Century, include:

- Suspension tuning that is 80 percent new for smooth yet agile handling.
- Rebound damper bumpers that are four times longer, for improved suspension cushioning.
- Retuned power steering systems for enhanced response and a more precise on-center feel at higher speeds.
- An all-new aluminum engine cradle and mounting assembly, for increased engine isolation, impact management and ride control.
- Wheel sizes increased by an inch to 16 inches on CX and CXL models; 17-inch wheels on the performance-oriented CXS.
- Lower aspect ratio tires with specially formulated tread patterns.
- Three levels of traction control, including GM's StabiliTrak stability enhancement system - a first for a midsize Buick.
- An all-new four-wheel-disc braking system with larger front rotors and calipers for improved performance and durability.
- Electronic brake force distribution, to account for vehicle loads, added to a new optional anti-lock brake system.

"QuietTuning" for segment-leading quietness

In addition to these changes, significant emphasis was placed on Buick's goal of providing best-in-class quietness. This initiative, called "QuietTuning," is an all-encompassing approach to reduce unwanted road, wind and engine noise and vibration levels throughout the entire body structure.

Specific examples include the use of:

- Acoustical laminate on the windshield and front side glass.
- Quiet Steel laminate on the front of the dashboard area.
- Extensive use of melt-on sound deadener in the underhood plenum, interior floorpan and cargo compartment areas.
- Sound-absorbing interior carpet backing and additional headliner pad coverage.
- A sound-absorbing layer under the instrument panel top pad and rear parcel shelf.
- Tightened body panel tolerances, additional foam inserts and redesigned seals and gaskets.
- Expanded baffles in the roof pillars, to block noise paths.
- Noise-reduction improvements in the 3800 Series III V-6 engine and the exhaust system. (Details in Powertrain section.)

"Engineers studied virtually every area of the LaCrosse to achieve the highest levels of quietness under any driving condition," said Affholter. "Using this integrated approach means that even small but carefully engineered changes can add up to a significant overall reduction in road and wind noise that will be appreciated by customers every time."

Comprehensive suspension retuning

The 2005 Buick LaCrosse uses the proven MacPherson strut coil-over-spring front suspension and trailing arm/tri-link rear suspension. Approximately 80 percent of the actual suspension components have been retuned from the Century/Regal models to provide a supple yet more controlled ride.

Two suspension levels are offered: LaCrosse CX and CXL are equipped with the standard suspension, while the Gran Touring suspension is standard on the LaCrosse CXS, matching its higher performance characteristics with a slightly firmer ride.

Specifically, the standard suspension incorporates constant-rate front springs that are about 20 percent stiffer than Century/Regal for a more controlled yet smooth ride. The front stabilizer bar remains at 30 mm, and is a tubular design that is "double isolated," also for a quieter, smoother ride.

At the rear, variable-rate springs also are 20 percent stiffer than before. The rear stabilizer bar has been increased to a 17-mm diameter and is now a tubular design, versus the 12-mm solid bar used in Century. The result is greater stability during hard cornering or braking while maintaining excellent ride and handling characteristics under normal driving conditions.

The Gran Touring suspension uses the same front and rear springs as the standard system, but employs slightly larger stabilizer bars (32 mm in the front and 19.4 mm in the rear) for an even flatter ride with improved handling response.

While both suspension levels use gas charged, four-stage dampers that reduce suspension float, one of the most significant tuning upgrades is the use of new, taller jounce and rebound bumpers within the damper modules to provide better control and cushioning.

Rebound bumpers, which dampen the suspension struts at their full downward limit, incorporate a new design that is softer but four times taller than Century/Regal (40 mm vs. 10 mm). Jounce bumpers, which provide earlier suspension control when severe bumps push the suspension up, are increased to 85 mm in length, from 65 mm. Additionally, an all-new front strut mount, made of a compound that provides twice as much damping as earlier designs, is used for the first time on any GM midsize car. These features combine to give the LaCrosse controlled body motions on road swells often found on secondary routes. They provide a secure and confident feel, without sacrificing ride isolation and comfort.

All-new four-wheel-disc brake system

All 2005 Buick LaCrosse models have an entirely new brake system that provides greater stopping power, increased durability, improved pedal feel and smoother overall operation.

The new Delphi system incorporates rear discs with solid rotors that are 270 mm in diameter and 14 mm in thickness. Front rotors are vented, and increased by 19 mm to 297 mm, with a 32-mm thickness. New non-asbestos organic linings replace semi-metallic linings, resulting in better cold-weather performance. An improved pedal feel is due to stiffer brake calipers, a shortened pedal ratio, and a recalibrated 260-mm booster.

An anti-lock braking system (ABS) is optional on the LaCrosse CX and CXL, and standard on the CXS. This Bosch 5.3 Series system reads input from speed sensors at each wheel to determine the level of pressure modulation to maintain vehicle control. The new system also incorporates an electronic brake force distribution feature, which monitors and adjusts brake pressure as needed and prevents rear wheel lockup when the vehicle is lightly loaded.

Three levels of traction control

Three levels of traction control are available on LaCrosse for 2005, each one providing added safety and driver control in wet or snowy conditions.

LaCrosse CX and CXL models are available with an engine-based enhanced traction control system that reduces engine power in varying degrees, depending on the rate of front wheel slippage.

Initially, the electronic brake control module sends a message to the powertrain control module to retard engine spark. If excess wheel slippage is detected, the PCM can also shut fuel delivery to as many as three engine cylinders, or even shift the transaxle into second gear until traction is restored.

GM's full range traction control system is standard in Lacrosse CXS. In addition to electronic engine management, this system applies the brakes at one or more wheels as required to restore traction.

For optimum vehicle control, GM's StabiliTrak stability enhancement system is available on the LaCrosse CXS - a first for any Buick midsize car. StabiliTrak incorporates ABS and traction control with an electronic stability system that constantly monitors steering angle, wheel speeds, brake pressure, lateral acceleration and yaw rates. If the driver is in danger of sliding or skidding, StabiliTrak instantly intervenes by adjusting brake pressure and engine power to help restore vehicle control. The system is automatic and functions at any speed, requiring no driver activation.

New aluminum engine cradle

All 2005 Buick LaCrosse models use a new engine cradle made of welded aluminum extrusions. The new design replaces the welded steel assembly used in the Century/Regal, and helps reduce transmitted vibrations into the passenger compartment. The cradle, which supports the engine, transaxle, steering and front suspension, weighs about 20 pounds less than the previous design, while providing better energy absorption and more controllable crush characteristics to reduce and manage impact forces away from the passenger compartment.

Recalibrated steering systems, Magnasteer on LaCrosse CXS

The steering systems on all LaCrosse models have been retuned for quieter operation, as well as a more precise on-center feel at higher speeds. Steering columns on the CXL and CXS models have tilt and telescopic adjustments as standard.

All models use a new T-bar, or shaft, inside the steering gear for improved balance between effort and control, and a new neoprene isolator in the intermediate shaft for significantly quieter operation and enhanced steering precision. LaCrosse CX and CXL models have a hydraulic assist, rack-and pinion system using a 15.3:1 steering ratio.

LaCrosse CXS models have as standard equipment Delphi's Magnasteer I power rack-and-pinion system, which uses a computer-controlled electromagnet to adjust steering effort, depending on vehicle speed. In low-speed maneuvers such as parking, it provides more assist for easier effort. Assist is reduced at higher speeds for a more direct response. The steering ratio is increased to a quick 13.2:1 for enhanced responsiveness.

In LaCrosse CXS models equipped with StabiliTrak, the Magnasteer II system uses the yaw sensor system from the StabiliTrak system to measure lateral acceleration and further adjust the steering effort for more response at higher speeds.

Larger wheels and tires

The standard wheel rim diameter for the 2005 Buick LaCrosse is increased to 16 inches, up from 15 inches on the Century. LaCrosse CX and CXL models are equipped with P225/60R16 Goodyear Integrity all-season tires, which have a high blend of dry and wet traction characteristics, low road noise and rolling resistance, and long tread life. Three wheel configurations are available, depending on model.

The performance-tuned LaCrosse CXS rides on 17-inch flangeless aluminum wheels and P225/55R17 Goodyear Eagle LS2 touring tires. A painted eight-spoke aluminum wheel is standard, with a chrome version optional.

The larger wheels and open eight-spoke design enable the use of larger brakes, and additional brake cooling. The low-aspect tires are formulated to deliver a quiet ride with responsive handling, making LaCrosse CXS a premium handling front-drive sedan.
 

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Originally posted by Rex Raider@Feb 3 2004, 07:27 PM


All-new four-wheel-disc brake system

All 2005 Buick LaCrosse models have an entirely new brake system that provides greater stopping power, increased durability, improved pedal feel and smoother overall operation.

The new Delphi system incorporates rear discs with solid rotors that are 270 mm in diameter and 14 mm in thickness. Front rotors are vented, and increased by 19 mm to 297 mm, with a 32-mm thickness.
Actually the front brakes are smaller than the current Regals (303mm)... larger than the measley 15" century system...

:p
 
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