2007 GMT-900 Information
Comprehensively redesigned chassis and suspension systems of the 2007 GM full-size SUVs are the backbone of a refined feel and effortless driving experience. The athletic, responsive tuning of the vehicles establishes a new benchmark for full-size SUVs, while providing the driver with a heightened feeling of control.
The all-new chassis, with wider front and rear tracks, and new coil-over-shock front suspension support ride and handling characteristics that reinforce the SUVs’ “live big, drive small” mantra. These components provide a more agile feel and help deliver an exceptionally smooth ride, enhanced quietness and an overall feeling of strength and stability.
“The strength of the new chassis supports the refined feel that is like no other full-size SUVs – vehicles that live big, but drive small,” said Terry Woychowski, vehicle chief engineer for full-size trucks. “The combination of a stronger chassis and refined driver control features helps give the vehicles an effortless, controlled and smooth driving experience.”
Features of the new chassis and suspension systems include:
Fully boxed frame
- A new, fully boxed frame that is significantly stronger and stiffer with hydroformed front and rear bay sections
- Wider front and rear tracks – approximately 3 inches (76.2 mm) in front and 1 inch (25.4 mm) in rear – enable increased stability, as well as a smoother, more controlled ride
- New coil-over-shock front suspension delivers linear, responsive ride and handling characteristics
- Highly refined five-link rear suspension (with variable-rate springs) delivers damped, isolated road feel and supports a variety of load-carrying capabilities
- Use of monotube Autoride shock absorbers for more controlled, real-time damping capability
- New rack-and-pinion steering system delivers precise, responsive steering and contributes to the vehicles’ “drive small” feel
- All-new four-wheel disc brake system larger vented discs, stiffer calipers, more robust apply system and standard next-generation Bosch ABS system provides shorter stopping distances, better pedal feel and quicker brake response
- Larger-diameter standard and available wheels and tires, including segment-largest, 22-inch designs available on Cadillac Escalade
- Standard StabiliTrak electronic stability control with first-time GM application of rollover mitigation – a software algorithm technology that uses system sensors to proactively predict vehicle “tip-up” and applies appropriate brake forces to prevent rollovers.
For the first time, GM’s full-size SUVs feature a fully boxed perimeter-type frame, the foundation on which the chassis, suspension, powertrain and body systems are mounted. Chevy Tahoe, GMC Yukon/Yukon Denali and Cadillac Escalade ride on a 116-inch (2,946 mm) wheelbase. Other models ride on a longer, 130-inch (3,302 mm) wheelbase.
The new, boxed frame design offers 49-percent increased torsional stiffness (side-to-side twisting) and 35-percent improved beaming frequency (front-to-back bending), compared with previous-generation vehicles. The stronger frame also supports an increased load capacity of approximately 5 percent.
The frame’s overall strength and increased stiffness are combined with more precise, integrated mounting brackets for powertrain, suspension and axle components, which enabled engineers to tune chassis and suspension bushings, springs and other elastomeric components for more accurate and refined ride and handling characteristics. The result is smoothness and responsiveness, with the capability expected of a full-size SUV. Quietness, a more linear driving feel and the feeling of isolation from the road also are enhanced.
A variable-height design of the boxed frame is matched with strategic application of high-strength materials throughout. The frame also has three distinct frame sections, or “bays,” each with specific strength and support characteristics. The front bay of the frameis an all-new design and features hydroformed frame rails made of high-strength steel.
The front bay includes the radiator support cross member, engine support cross member and front lower control arm cross member, all of which are welded to the hydroformed frame rails. GM pioneered the use of hydroformed frame rails for full-size SUVs on the previous-generation vehicles, introduced in 2000. The process uses highly pressurized fluid – up to 20,000 psi – to shape the frame rails. The revised design of the 2007 full-size SUV front bay section is approximately 40 percent stiffer than the previous-generation without a significant difference in mass.
A new powertrain mounting system is part of the front bay section. It is welded to the engine cross member and includes very stiff mounting brackets for the engine and transmission. The brackets house unique elastomeric bushings (on vehicles not equipped with Displacement On Demand) to dampen vibrations and foster a smoother ride and feel inside the passenger compartment. Vehicles with Displacement on Demand-equipped powertrains used hydraulic mounts to accommodate the changing rotational forces associated with the cylinder-deactivating technology.
The middle bay section of the frame extends from the A-pillar area to the C-pillar area. The boxed side rails of the middle bay support three stiffness-enhancing cross members. Strength also is built into joining of the front bay to the middle bay, with the front bay’s hydroformed rails slipping inside the boxed sections of the middle bay. This shingle-type design is welded and reinforced with a high-strength steel close-out plate that covers the overlapped joint.
The side rails of the middle bay section are constructed of two pieces of high-strength steel that are welded to form the sturdy box design. The outer section is made of 60-ksi steel that is 3.3 mm thick; the inner section is made of 30-ksi steel that is 2.2 mm thick. The rails also have a variable-height construction (between 110 mm and 210 mm) that enables strategic placement of strength-enhancing materials in certain areas for a more integrated, lower-mass design.
The rear bay frame section extends rearward from the C-pillar. Like the front bay section, its boxed rail sections are hydroformed and are joined to the middle bay with an overlapping, shingle-type construction. The rear bay section offers enhanced strength via a stronger, single-piece spare tire cross member, a more robust fuel tank carrier cross member and a thicker rear track bar cross member for the five-link rear suspension.
Wider front and rear tracks
The 2007 full-size 1500-Series SUVs have wider front and rear tracks than previous-generation models. The front track is more than 3 inches wider (77 mm) – 68.2 inches (1731.8 mm) vs. 65 inches (1651 mm). The rear track is more than 1 inch wider (25 mm) – 67 inches (1701.8 mm) vs. 65.98 inches (1675.8 mm).
A wider track promotes overall vehicle stability and a lower center of gravity, which the driver and passenger can feel through the vehicle’s secure ride and handling attributes, as well as flatter, more controlled cornering. The wider track widths also enhance smoothness.
Coil-over-shock front suspension
A new coil-over-shock front suspension is used on all light-duty models, along with a new front axle mounting system. The coil-over configuration offers smoother, more precise and nimbler ride and handling characteristics, especially with the larger wheel-and-tire combinations offered on the new SUVs. Vibration and harshness also is greatly reduced when compared to the previous-generation torsion bar front suspension design.
The new suspension system uses specially tuned coil springs and 46-mm monotube shock absorbers (except vehicles equipped with Autoride), along with steel upper control arms and forged aluminum lower control arms. The aluminum lower arms reduce un-sprung mass by approximately 20 pounds (9 kg) and the responsive monotube shocks bolster the vehicles’ more nimble driving feel.
Complementing the coil-over suspension design are new, stiffer frame attachments for the suspension components and a new, four-point front axle mounting system. These stiff, accurate mounting points – including softer bushings located within brackets of the stiff front bay frame section – contribute to the vehicles’ more controlled and linear driving feel.
Five-link rear suspension
A five-link rear suspension is used for 1500-Series 2WD and 4WD models (a heavy-duty leaf spring design is used on 2500 models). Although similar in design to previous models, the 2007 SUV rear suspension features a more robust rear axle design that offers increased payload weight. The axle system enhancements include a stiffer track bar bracket mounted to the rear bay frame section, a redesigned axle carrier and an axle rear cover that is 50 percent thicker for increased strength and durability.
Like the front suspension, the rear suspension uses new, stiffer frame mounts for suspension component attachment, along with variable-rate springs and monotube shock absorbers (except when equipped with Autoride). The accuracy and responsiveness of the tuned springs and monotube shocks provide superior dampening and ride control, regardless of whether the vehicle is carrying or towing a heavy payload.
Autoride real-time damping system
Vehicles equipped with the Z55/G59 suspension package include the segment-exclusive Autoride bi-state, real-time damping system. This advanced system enables an extremely refined ride with greatly reduced body motion. It also delivers instant suspension response to wheel speed, body position, vehicle speed, steering angle and braking.
Autoride is a semi-active, two-position damping control system that responds in real time to road conditions and driving conditions, based on body and wheel motions determined through sensors positioned at all four corners of the vehicle. The system uses up to four two-position monotube shock absorbers (each with an internal solenoid valve and air-lift/auto-leveling capability), four wheel-position sensors, a steering position sensor, engine torque monitor, brake apply sensor, vehicle speed sensor and an independent controller. Independent damping control at each corner of the vehicle allows specific damping to control body motions during higher-speed turns and driving over uneven surfaces.
Autoride’s air-lift/auto-leveling system includes air bags located over the shocks. An integrated air pump automatically adds air, when needed, to increase pressure in the air bags, raising the suspension to level the vehicle’s ride height when carrying passengers or a heavy payload. Conversely, air is bled from the bags when the payload is removed, returning the vehicle to a level ride height.
The 2007 full-size SUVs are available with three distinctly tuned suspension systems, each tuned to provide an optimized ride with smoothness, a greater feeling of isolation from the road and minimal body movement:
Both the ZW7 and Z71 suspensions use 46-mm front and rear monotube shock absorbers and tuned springs. The shocks feature large rod diameters that help reduce shock lag and fade over time. The ZW7 suspension uses variable-rate rear springs – an uncommon feature in the segment – to maintain body height and attitude under various payload conditions.
- ZW7 Premium Smooth Ride: standard on 2WD and 4WD Chevy Tahoe and Suburban, GMC Yukon , Yukon XL, Yukon Denali and Yukon XL Denali
- Z55 (includes Autoride): standard on Cadillac Escalade, Escalade ESV and Escalade EXT; available on Chevy Tahoe and Suburban, GMC Yukon , Yukon XL, Yukon Denali and Yukon XL Denali
- Z71 Off Road: available on 4WD Chevy Tahoe and Suburban, GMC Yukon and Yukon XL
The unique Z55 suspension with Autoride uses automatically controlled air bags to regulate body height when the vehicle is loaded or unloaded. It also uses springs made of micro-alloy steel, which is stronger than typical spring steel yet offers mass savings.
All three suspensions have distinct bushing, spring and material characteristics. The firmness of the bushings, the spring rates and related materials were carefully selected after countless hours of comparison testing at GM’s proving grounds and real-world testing on roads of varying conditions throughout North America . Suspension tuning also is specific to the size of the wheels and tires, as the 2007 SUVs offer a range of wheel sizes from 17 to 22 inches.
Rack-and-pinion steering system
For the first time on GM’s full-size SUVs, a hydraulic power-assisted rack-and-pinion steering system is employed. The result is an optimized on-center steering feel and more immediate, precise steering response.
The new system mounts on the engine cross member of the front bay frame section, directly beneath the engine. This mounting position uses the inherent stiffness of the frame to enhance the direct and linear feel of the steering system, reducing the driver’s need for continuous corrections during turns and sweeping corners. On 4WD vehicles, the steering rack is located forward of the front differential.
Steering ratios vary, depending on the vehicle’s suspension choice and wheel size. Combined with more immediate responsiveness, this gives the new 2007 full-size SUVs an easier, more maneuverable feel, particularly when parking in tight quarters. Low-friction, highly precise ball-and-needle bearings within the steering system contribute to the precise and immediate feel from the steering wheel. The system also is engineered with low-noise valve technology that helps reduce noise and vibration.
Four-wheel disc braking system
A new brake system design with larger four-wheel discs and an all-new ABS system helps GM’s new full-size 1500-Series SUVs deliver superior braking performance with assuring pedal feel. The system includes larger-diameter rotors, stiffer front calipers and longer-life brake pad linings.
The front rotors measure 13 inches in diameter (330.2 mm), an increase of 1 inch (25.4 mm) – approximately 15 percent larger. The front rotors also are thicker with large cooling vents, providing enhanced performance and durability. The cast iron, dual-piston front brake calipers are 50 percent stiffer than before, which reduces the tendency for flexing during hard or prolonged braking. The stiffer calipers, along with dual pistons, contribute to a more direct, linear and stronger brake pedal feel.
At the rear, the standard vented discs measure 13.5 inches (342.9 mm), an increase of 0.5 inch (12.7 mm) – approximately 7.5 percent larger. A revised single-piston rear brake caliper design contributes to reduced brake noise and more immediate braking response. Both the front and rear brakes use new, non-asbestos brake pad linings that can deliver up to 40,000 miles of performance during normal use.
The new brakes are complemented by a new, twin-piston design brake application system, including a larger master cylinder and active brake booster. The more robust design enabled engineers to tune the application system to optimize pedal feel and brake system responsiveness. The system requires less pedal pressure to provide a more immediate brake response, delivering a dramatically improved feel.
A next-generation Bosch 8.0 ABS system is standard on all 2007 full-size SUVs. It has more precise valve control that requires less cycling of fluid from the brake master cylinder, resulting in reduced noise and enhanced braking feel when ABS is activated during a braking event. The new ABS system also is less complex and has reduced mass when compared with the previous system.
StabiliTrak electronic stability control
GM’s sophisticated StabiliTrak electronic stability control system is standard on all 2007 full-size SUV models. Partnered with the new brake system and four-channel, four-sensor electronic brake controls, the system provides more precise, controlled ABS stops, as well as enhanced traction/yaw stability. The new, larger brake system allows for smoother, quieter StabiliTrak interventions and includes an active vacuum booster to increase system response time to changes in vehicle behavior.
On 4WD models, StabiliTrak uses brake control to precisely control the speed of each wheel and manage torque across the front and rear axles. On 2WD models, the system precisely controls the speed at each wheel and manages side-to-side torque on the rear differential. Individual brake sensors at each wheel provide instant signals to the control module, enabling it to aggressively adjust brake pressure. However, traction is controlled by transferring torque across the rear axle – rather than front and rear axles, as in 4WD models. When the vehicle is on a slippery surface, the traction system increases torque to the rear wheel that has the most traction.
On 2WD and 4WD models, the vehicle brake system provides the torque-biasing to enhance traction and engine management is used, as required, to assist in controlling traction and yaw stability. The Autotrac transfer case’s control algorithm has been integrated with the StabiliTrak and ABS systems to provide enhanced vehicle stability by managing the front-to-rear torque distribution.
StabiliTrak is always on and fully functional. It is automatically enabled, providing full stability, traction and ABS control, whenever the vehicle operates in forward gears. The system intervenes when it senses one or more of the wheels slipping or when the vehicle is not following the driver’s intended path. It detects slippage during braking or acceleration and automatically adjusts individual wheel brake pressure, engine torque and, on 4WD Autotrac models, adjusts front to rear drive torque distribution, as required, to achieve optimal control.
The Stabilitrak system has new rollover mitigation technology. This technology adds software algorithms that use Stabilitrak sensors to proactively predict vehicle “tip up” on a flat road surface, and applies brake force to the outside front and rear wheels in order to reduce lateral force in the vehicle. This brake force intervention can help reduce the likelihood of a rollover in certain circumstances.
Wheels and tires
Complementing the strong, athletic styling of the 2007 full-size SUVs is a range of large standard and available wheel and tire sizes, including segment-largest 22-inch wheels and tires available on the Cadillac Escalade. New P-metric tires for 18-, 20, and 22-inch sizes have a nylon cap ply that enhances strength and durability.
Chevy Tahoe and Suburban, along with GMC Yukon and Yukon XL, come standard with 17-inch wheels and touring tires that provide excellent comfort and low road noise. Uplevel models offer styled aluminum wheels – different designs for Chevy and GMC models – including machine-face and polished-face wheels. Tahoe, Suburban, Yukon and Yukon XL also offer optional 20-inch wheel-and-tire combinations, including six-spoke, bright-face aluminum wheels. Eighteen-inch wheels are standard on GMC Yukon Denali and Yukon XL Denali, with 20-inch wheels optional.
Cadillac Escalade models come standard with 18-inch aluminum wheels, with a 22-inch wheel-and-tire combination optional. Both the 18-inch and 22-inch wheel designs have a new seven-spoke design that is specific for Cadillac models. Standard 18-inch wheels have a machine-face design, with chrome appearance available.
# # #