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Cadillac STS (2005) -
Unmistakable Design

Cadillac STS cutaway - click to enlarge

The 2005 Cadillac STS is the luxury nameplate’s large performance sedan. It has been designed, engineered and executed to deliver precision craftsmanship, outstanding performance, and sophisticated luxury in a distinctly American package.

Based on General Motors’ new rear-wheel-drive Sigma architecture, which also is the foundation for Cadillac’s entry-luxury CTS sedan, CTS V-series high-performance sedan, and SRX luxury performance utility – the STS is designed to compete head-on with world-renowned prestige sedans in markets around the globe.

The STS is equipped with two engine offerings, including a 320-horsepower 4.6-liter Northstar V-8 with 315 lb-ft of torque, or 3.6-liter 255-horsepower V-6 with 252 lb-ft of torque. The STS also is available with all-wheel-drive (AWD) on vehicles equipped with the Northstar V-8. The 4.6-liter Northstar delivers 0 to 60 performance at or less than 6.0 seconds. With the V-6 or AWD V-8, the STS achieves 0 to 60 performance in under 7.0 seconds.

The V-6 and V-8 are mated to electronically controlled five-speed automatic transmissions – the Hydra-Matic 5L40-E is mated with the V-6, and the Hydra-Matic 5L50-E is mated with the V-8 and has both rear- and all-wheel-drive applications. The 5L50-E is designed to handle the V8’s torque, with a 25 percent torque capacity increase over that of the 5L40-E.

Cadillac STS cutaway - click to enlargeThe 60-degree 3.6-liter V-6 is a highly refined, DOHC four-valves-per-cylinder engine with all-aluminum construction. The valve train configuration includes roller finger followers. The adoption of fully variable valve timing for both intake and exhaust valves provides outstanding flexibility, fuel economy and emissions reduction. The four-cam variable valve timing is a key element in the V-6’s control strategy, which gives the engine a wide-ranging flexibility. For example, 90 percent of the 3.6L V-6’s peak torque is available across a remarkably broad operating range: from 1,600 rpm to 5,800 rpm. In addition, an electronically controlled throttle (ETC) effectively coordinates the driver’s intentions with the actions of the various control components.

Cadillac STS cutaway - click to enlargeThe 4.6-liter Northstar V-8 is a 90-degree DOHC four-valve-per-cylinder engine, with an aluminum block and cylinder heads and valve train with roller finger followers. The Northstar is equipped with a host of technologies, including four-cam continuously variable valve timing (VVT) for improved performance, refinement, economy and emissions; electronic throttle control, providing additional driving refinement. This allows the engine control system to precisely and seamlessly tailor vehicle performance to the driver demands; and low restriction intake and exhaust manifolds and cylinder head ports designed to ensure optimum airflow and cylinder-to-cylinder distribution for maximum performance and emissions control.

Rear-wheel-drive STS offerings (V-8 and V-6) offer an available limited slip differential, which mechanically limits wheel spin on all surfaces for improved vehicle performance during handling maneuvers. Vehicles equipped with the V-6, which are only available in rear-wheel-drive, have a performance-optimized drive ratio of 3.42. Vehicles equipped with the V-8 engine are available with three final drive ratios configurations; 2.73 for enhanced fuel economy; 3.23 for mid-sport performance; and a 3.42 for optimized performance. Exported vehicles are only equipped with the 3.42 final drive.

Vehicles equipped with all wheel drive (V-8-equipped vehicles only) have a final drive ratio of 3.23. The system incorporates a 40/60 rear bias torque split to provide the STS with superior handling performance, acceleration, traction, and control for dry, wet, icy, and snowy road conditions. Its three open differential layout, coupled with four-wheel traction control, balances driving torque distribution to each wheel and minimizes wheel spin to optimize on-road performance.

The V-8 and V-6 are mated to electronically controlled five-speed automatic transmissions – the Hydra-Matic 5L50-E is mated with the V-8, and the Hydra-Matic 5L40-E with the V-6. Both transmissions incorporate Driver Shift Control (DSC) and Performance Algorithm Liftfoot (PAL) technologies. Driver Shift Control enables the driver to switch from automatic to a clutchless five-speed high-performance manual transmission. Once the driver moves the gearshift lever into DSC mode, a quick tap is all that is required for smooth, crisp upshifts or downshifts within a selected range. Performance Algorithm Liftfoot inhibits upshifts while maintaining engine braking following continuous performance driving. The transmission control module (TCM) monitors driver behavior to determine whether or not to enable this feature. For example, if the system detects a drop in vehicle speed prior to entering a turn or a lane change, up to two downshifts can occur to provide the driver with maximum vehicle performance.

Cadillac STS cutaway - click to enlargeWhile the all-new 2005 STS is true to the Cadillac’s performance-oriented roots, a host of chassis refinements ensure that it hits the “sweet spot” of ride and handling. The result is a ride that keeps drivers fresh and comfortable without sacrificing the driving experience. Road impacts and other harsh inputs are effectively absorbed and dissipated through ride-tuned tires, dampers, suspension components and bushings, as well as improved structure in body-to-chassis interfaces and additional refinements in the engine mounts.

Among the many refinements found in the front suspension components is the use of aluminum for both the upper and lower control arms, knuckles, and brake calipers, reducing overall mass and contributing to nimble handling and dynamic wheel control. Reduced unsprung mass requires less damping and provides better road-holding ability. Hydraulic control arm front bushings also are used for good motion control and to minimize high-speed road vibration by damping energy transmitted to the vehicle structure. A hollow front stabilizer bar on all models brings weight savings and added stability. Front shocks on base models are monotube dampers from Sachs, a leading German producer of high-performance shock absorbers, which provide highly responsive damping of road inputs. The STS also offers the award-winning Magnetic Ride Control (MR).

The fully independent multilink rear suspension with fully isolated sub frame is an uncompromising design with excellent suspension kinematics that enables outstanding ride and handling performance.

At the same time, the other features of the suspension architecture give it the ability to control loads and maintain stability during dynamic driving situations, striking a balance between ride quality and high-performance handling capability.

The engine cradle on the STS, which is solid-mounted to the engine rails for more precise feel, has high stiffness for noise isolation and optimum handling and safety performance. It has six attachment points (two more than typical for a performance sedan) to better handle heavier drive loads and energy pulses, especially in V-8-equipped versions.

Steering input to the driver and handling are enhanced due to a premium ZF Servotronic II rack-and-pinion speed-sensitive steering gear (optional) with 18.2:1 variable ratio, speed-sensitive variable assist, and a turning radius as little as 11.5 meters. The ZF steering system incorporates outstanding torsional stiffness with less operating friction. The result is steering which is very precise, with highly linear response and extremely smooth, predictable transitions.

One of the most distinguishing ride and handling features of the STS will be the optional Magnetic Ride Control (MR) system. This technology, which uses electronic control of damping forces in a continuously variable real-time damping system to provide exceptional responsiveness, greatly increased driver control and increased tire contact with the road, regardless of road surface. In addition, the MR system on the STS is among the first to make available two selectable settings accessed through the infotainment display head – a performance or touring mode.

The standard StabiliTrak system on the STS is a sophisticated four-channel (independent control to all four corners of the vehicle) active handling system. It links the vehicle’s dynamic control systems to assist the driver in maintaining control under demanding or adverse conditions such as wet, snow-covered or icy roads, tight turns, and evasive maneuvers.

The STS is equipped with four-wheel-vented disc brakes with standard four-wheel antilock braking system (ABS) and traction control system (TCS). The brakes feature vented rotors consistent with the demands of a luxury performance sedan, and aluminum calipers (twin-piston front, single-piston rear) to reduce weight. Base brake package rotor dimensions are 303 x 32 mm front and 298 x 26 mm rear. Uplevel brake package rotor dimensions measure 323 x 32 mm front and 320 x 26 mm rear. Panic Brake Assist (PBA), which senses emergency braking by detecting the speed or force the driver applies to the brake pedal and boosts the power as needed, is incorporated into the brake system.

The technological backbone of the STS comes in the form of the GM LAN Serial Data Electrical Architecture – a high- and low-speed data network that connects system modules and ensures that information is properly communicated and shared between them. Keyless Access enables passive vehicle and trunk entry and push-button ignition via a personalized, keyless fob. With the key fob in a pocket or purse, a person can approach a locked vehicle, pull the door handle and open the door. The same concept applies when opening the trunk. The Smart Remote Start system, which operates from as far as 200 feet, not only starts the vehicle via fob activation but also automatically adjusts a variety of personalization settings in the process. The STS can be equipped with Adaptive Cruise Control (ACC), which greatly increases the value and comfort of cruise control, especially in congested traffic situations.

The STS is equipped with large 70-millimeter projector beam headlamps for outstanding forward- and spread-light performance. Two projector beams are stacked vertically in each headlamp housing; the upper projectors provide low-beam illumination, and all four projectors are illuminated for high-beam performance. Intellibeam automatically switches headlamps from high- to low-beam and back again when oncoming headlamps or forward lighting elements are sensed. The system makes nighttime driving safer by providing the maximum amount of light possible for any driving scenario.

The STS is the most advanced luxury performance sedan yet from Cadillac, and another step towards matching European performance standards.

Gm.com © 2005

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Cadillac STS

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