Engineers developed 11 all-new, fully boxed frame assemblies to improve durability and ride characteristics and support increased capabilities.

The details: The frames have increased cross sections and use more high-strength steel for greater durability, higher towing capacity and improved ride and handling; the front sections are hydroformed. The bending and beaming stiffness of the frames is increased 92 percent and 20 percent, respectively, with the fully boxed sections enhancing torsional stiffness by a factor of five. Also, larger engine and transmission mounts, coupled with a 125-percent-stiffer front frame structure, provide greater vibration control, while hydraulic body mounts are incorporated under the cab section on extended and crew cab models for a more isolated feel inside. Engineers addressed common customer and aftermarket uses when designing the new frames, including adding access holes to the rear frame section to enable easier installation of fifth-wheel/gooseneck-style hitches. Also, the frame-mounted hitch for conventional trailering is stronger, with a box-tube design. It supports up to 16,000 pounds (7,257 kg).

Sierra HDs feature a new, stronger independent front suspension – enabling snow plow installation on all 4WD models.
The details: A completely redesigned independent front suspension system offers up to a 25-percent greater front axle weight rating – up to 6,000 pounds (2,721 kg) front gross axle weight rating (FGAWR) – so a snow plow can be used on all 4WD cab configurations with the available snow plow prep package. Sierra’s signature short-long arm/torsion bar front suspension design is retained, but now features new, forged steel upper control arms that are stronger and lighter than their predecessors.

The new lower control arms are made of precision-machined cast iron to handle the greater loads. Five different torsion bar rates support five different front gross axle weight ratings (a single torsion bar was previously used for all models). This helps stabilize the range of trim heights of various models under load, while enhancing appearance, handling, durability, tire wear and alignment. The trim height is adjusted on each bar via a single bolt, easily allowing the height to be changed to account for the weight of a snow plow or other accessories. The Sierra HD front suspension now uses a pair of urethane jounce bumpers on each side, instead of one, for improved load management; and there’s a new upper shock mount attachment design that’s positively connected to the frame with two fasteners. This design eliminates squeaks and clunks, while supporting higher load capability and increased durability.

COMPETITIVE FACTS: Compared to competitors’ beam-axle front suspensions, the Sierra’s independent front suspension provides a better ride, more accurate trim height control (with fewer parts) and greater flexibility to adjust the alignment for weight and tire sensitivity.

A new asymmetrical leaf-spring rear suspension supports greater loads.
The details: Matching the Sierra HD’s greater strength and capability is a rear suspension designed to support greater loads. It features a new, larger asymmetrical leaf-spring design that also contributes to improved ride and handling characteristics. The asymmetrical design is derived from unequal front and rear spring half lengths, which minimize axle hop and enhance traction control efficiency. 2500HD models feature a two-stage leaf-spring design, while 3500HD models have a three-stage design. All models feature 3-inch-wide (76 mm) leaf springs that are 20-percent wider than previous models. The larger leaf-spring design supports increased rear gross axle weight ratings across the board. On the 2500HD models, the rating is 6,200 pounds (2,818 kg) – up from 6,084 (2,765). On 3500HD models, the rating increases to 7,050 pounds (3,204 kg) on single-rear-wheel models and 9,375 pounds (4,261 kg) on dual-rear-wheel models – the latter representing a nearly 14-percent increase over the previous 8,200-pound (3,727 kg) rating.

Sierra HDs deliver a more refined driving experience, with more capable ride, handling and steering.

The details: Longer wheelbases – ranging from 133.6 inches (3,395 mm) to 167.7 inches (4,259 mm) – and wider front/rear tracks enhance the ride and handling characteristics of the Sierra 2500HD and 3500HD, giving them a greater feeling of smoothness and control. The longer wheelbases and wider tracks are complemented by the new, stiffer frames, new jounce bumpers, shock mounts and hydraulic body mounts to provide a solid, smooth and isolated driving experience. New shocks were specially valved to support the new trucks’ weight ratings, while balancing excellent ride characteristics. Also enhancing the driving experience is a revised steering system designed to support the trucks’ greater front gross axle weight rating. It includes a new, larger steering gear, power steering pumps and linkages. The pumps (different parts for gas and diesel models) deliver greater pressure for reduced steering effort in low-speed and parking maneuvers; they are also quieter. On some models, the new linkages feature a compliant joint added at the pitman attachment to enhance handling.

The new 6.6L Duramax turbo diesel delivers segment-leading torque and up to 63-percent lower NOx emissions; and is B20-capable.
The details: The workhorse Duramax 6.6L turbo diesel V-8 is more powerful and durable for 2011, delivering segment-best horsepower and torque – 397 horsepower (296 kW) at 3,000 rpm and 765 lb.-ft. of torque (1,037 Nm) at 1,600 rpm – lower emissions and B20 biodiesel capability that promotes a domestically produced renewable fuel. The new Duramax 6.6L features:
  • NOx emissions reduced at least 63 percent over 2010 models
  • Quieter operation
  • High-pressure (30,000 psi/2,000 bar) Piezo-actuated fuel system for greater fuel efficiency, improved performance and reduced emissions
  • “Smart” exhaust brake feature that enables controlled vehicle slowdown on downhill grades without actuating the brakes
  • Selective catalytic reduction after-treatment system using diesel exhaust fluid (DEF) injection to provide the best overall diesel characteristics and performance – with a range of about 5,000 miles (8,000 km) between DEF refills
  • Combustion and after-treatment have been optimized to provide about 700 miles (1,125 km) between diesel particulate filter regenerations – a 75-percent improvement over the previous system and a significant contributor to improved fuel efficiency, as the regeneration process requires additional fuel
  • B20 biodiesel capability for an alternative fueling option
  • Internal revisions that improve durability.
With nearly 1.3 million Duramax 6.6L engines produced since 2000, they have proven exceptionally durable and dependable. The internal elements that helped build its reputation are enhanced for 2011, including: