Stronger Chassis, Enhanced Body Structure Contribute to Greater Comfort, Quietness in 2015 GMC Yukon/Yukon XL
NAPA, Calif. – A stronger chassis, stronger body structure and comprehensive chassis and suspension enhancements contribute to a quieter, more-controlled driving experience in the 2015 GMC Yukon family.
That driving experience is rooted in a stronger, fully boxed, perimeter frame that supports payload and trailering capability that body-frame-integral crossovers and SUVs can’t match. It’s complemented with new technologies, including electric power steering, to elevate the Yukon’s refinement while ensuring uncompromising capability.
“ New and revised suspension, steering and brake enhancements work collectively on the 2015 GMC Yukon family to produce a more solid-feeling, smoother and quieter ride – without sacrificing the capabilities Yukon customers demand,” said Jason Petric, vehicle system engineer. “Customers will immediately notice higher levels of noise isolation, along with a more-assuring feeling of solidity in the body and smoothness in the suspension. They contribute to a more direct driving experience that can make these full-size SUVs feel and drive like smaller vehicles.”
New and enhanced chassis and suspension features include:
- A wider rear track that contributes to a more planted stance
- Stronger body structure with more high-strength steel for a more solid feel and quieter cabin
- Shear-style body mounts, which reduce body shake and enhance the feeling of structural stiffness, improve damping performance when compared with previous compression mounts
- Addition of a cross-axis ball joint on the frame-side of the rear suspension lateral link that enhances steering precision
- Third-generation magnetic ride control is standard on Denali. Its new, dual-electric-coil design enabled engineers to tune with more resolution to handle quickly changing road conditions
- Eighteen-inch standard wheels are a half-inch wider, reducing tire flex for improved cornering performance . Twenty- and 22-inch wheels are available
- New, electric variable-assist power steering system enhances fuel economy and tailors steering assist to vehicle speed
- New four-wheel-disc brake system with Duralife™ brake rotors that offer up to double the service life
- Revisions that improve pedal feel for more-confident braking performance.
Along with a smoother, more refined ride, the Yukon’s chassis and suspension support excellent cargo-hauling and trailering capabilities. Yukon offers a maximum payload rating of 1,676 pounds and, when properly equipped, a trailering rating of 8,500 pounds. Because of the additional vehicle weight that comes with its longer length, the max payload for Yukon XL clocks in at 1,655 pounds and the maximum trailering rating is 8,300 pounds.
A firmer foundation
The fully boxed, high-strength-steel-intensive ladder-type frame of Yukon and Yukon XL enables an optimal balance between hauling capability, noise and vibration isolation and safety. The frames for each vehicle are similar in design and construction, but the Yukon XL’s is longer, to support its 14-inch-longer wheelbase and roughly 20-inch-greater overall vehicle length.
The frame design and construction incorporates much of the technology and materials used on the 2014 Sierra pickup, including more than 75 percent high-strength steel and new body mounts that enhance ride and handling.
To optimize strength and refinement, three sections comprise the frame: front bay, mid bay and rear bay. The front and rear frame bays use hydroformed side rails. GM pioneered the use of hydroformed frame rails for full-size trucks and SUVs nearly 15 years ago. The process uses highly pressurized fluid to shape the frame rails, making them stronger and lighter than comparable welded multi-piece components.
A four-point, front-axle mounting system is integrated with the front bay and uses strong axle mounting brackets that, combined with the front bay’s stiffness, significantly reduces vibration compared to previous models.
New, boxed side rails of the frame’s middle bay are constructed of two pieces of high-strength steel welded to form the sturdy box design, which supports two stiffness-enhancing cross members. Strength is also built into the frame by slipping the front bay’s rails inside the boxed sections of the middle bay 9.4 inches (240 mm), creating a very rigid structure that resists bending.
The hydroformed rear bay is joined to the middle bay with an overlapping, shingle-type construction. They offer enhanced strength over the previous model, with a robust fuel tank cross member and a stronger, single-piece spare tire cross member. The rails are thicker where carrying strength is needed and tapered toward the rear to reduce weight and improve ride characteristics.
Stronger body structures and new shear-style body mounts
The 2015 Yukon models feature more robust body structures mounted on the stronger frames, contributing significantly to their more solid feel and a quiet, smooth ride. The bodies incorporate greater use of high-strength steel and ultra-high-strength steel, which also contributes to improved crashworthiness.
Compared to conventional steel used in most body structures, the yield and tensile strength of high-strength steel is about four times greater, while ultra-high-strength steel – which can include boron steel – is up to four times stronger than high-strength steel, and eight times stronger than conventional steel. This allows strategic parts to be made of thinner-gauge panels, for reduced weight, while still offering the same – or greater – strength of otherwise thicker, heavier components made of conventional steel.
High-strength steel and ultra-high-strength steel is used in the A-pillars and B-pillars, the inner roof rails and additional reinforcements for roof-crush protection. It is also included in the rocker panels, door rings and other underbody components.
Additionally, a number of structural reinforcements and other components help stiffen the body, for noticeably reduced vibrations on rough surfaces. For example, strong, diagonal braces were added underhood to better tie the front end to the body. Further, an enhanced instrument panel support beam, which spans the width of the interior under the dashboard, features a new beam-to-floor brace that is four times stronger than before. It’s used with stronger instrument panel mounting brackets and a thicker tubular steering column jacket to enhance the steering column’s stiffness, reducing vibration that could otherwise be felt in the steering wheel.
New, shear-style body mounts complement the stronger body structure to significantly improve lateral stiffness and contribute to a smoother ride. They are bolted to the frame and provide dampening in both compression and rebound, meaning the tension generated during compression is released in a controlled manner, similar to a shock absorber. Previous body mounts worked in compression only. Also, engineers were able to more precisely tune the mounts for dampening in multiple directions – up/down, cross-vehicle and fore/aft – for reduced body shake.
The new SUVs’ stiffer chassis enabled more precise tuning of the front and rear suspensions, for smoother, more confident performance than previous models – and less vibration and shake, particularly on harsh terrain. The incorporation of more lightweight materials and revised rear suspension geometry also contributes to a more responsive feel.
Three suspension packages are offered:
- ZW7 – Premium Smooth Ride, incorporating revised twin-tube shocks that offer greater damping at low speeds, a premium suspension. It is standard on SLE and SLT.
- Z85 – Premium Smooth Ride with Air Control , which constantly senses and adjusts the rear suspension height until it is level. It is part of the heavy-duty trailering package available on SLE and SLT.
- Z95 – Third-Generation Magnetic Ride Control . Standard on Denali, it’s the world’s fastest-acting suspension – a real-time damping system that delivers more precise body motion control. It “reads” the road every millisecond and changes damping in just 10-15 milliseconds in shocks filled with a magneto-rheological (MR) fluid containing minute iron particles. Under the presence of magnetic charge, the iron particles align to provide damping resistance almost instantly.
All models – 2WD and 4WD – feature an updated coil-over-shock independent front suspension design, with forged aluminum upper control arms and cast-aluminum lower control arms. They are 12 pounds lighter per side and 10 percent stiffer than comparable steel components.
The front suspension also uses new cast-aluminum steering knuckles that are 9 pounds lighter per side than previous models and deliver comparable stiffness, along with coil springs that are up to 30 percent stiffer than before, for more confident handling. Enhanced jounce bumpers, spring isolators and top shock mounts are additional suspension upgrades that also contribute to ride quality and noise isolation.
At the rear, all models feature a five-link coil-spring suspension design, which enables optimal ride and handling through more precise tuning. Lateral stiffness was increased at the frame-side joint of the lateral link with the addition of a cross-axis ball joint, in place of the previous rubber bushing. The result is a greater feeling of steering precision.
A wider rear track – 68.7 inches (1,744 mm) – and half-inch wider wheels improve stability and ride smoothness. The new geometry also contributes to flatter, more confident-feeling cornering, particularly when hauling heavy cargo or towing. The wider wheels reduce tire flexing and new-design twin-tube shock absorbers (ZW7 rear) and mono-tube shocks (ZW7 front / Z85 front and rear) improve low-speed damping for a smoother, more controlled ride.
Additional chassis and suspension features include:
- A more robust 9.5-inch rear axle design that offers improved durability, noise and vibration characteristics and a larger ring gear to handle the increased torque of the 5.3L engine. It’s available with 3.42 and 3.08 axle ratios
- New dual-path shear upper shock mounts that help isolate road input and create more control
- Repositioned s hock absorbers that are placed for the best possible control of suspension movement over rough surfaces
- Standard automatic locking rear differential that provides greater traction when needed and greater driving comfort when it’s not
- Range of 18-, 20- and 22-inch regular-production aluminum wheels.
Efficiency-enhancing electric power steering
All Yukon models feature new electric variable-assist power steering, which improves overall vehicle handling and reduces steering effort at low speeds. Because there is no engine-driven pump, electric power steering also saves fuel and eliminates the maintenance associated with hydraulic power steering.
The steering calibrations are tailored for the Yukon and Yukon XL’s respective wheelbase lengths, while the variable assistance enhances overall handling with reduced steering effort in parking lots and a higher rate on the highway that provides a more solid, direct and on-center feel.
Longer-lasting Duralife ™ brakes
Four-wheel disc brakes, with four-channel ABS, are standard on all models and feature new Duralife™ brake rotors that were introduced on the 2014 Sierra. They offer up to double the service life of conventional rotors and enhance braking performance, thanks to a GM-exclusive manufacturing process that protects against rust that, over time, can lead to steering wheel shudder.
The process involves super-heating the rotors to more than 1,000 degrees F (560 C) for an entire day in a special oven, where the nitrogen-rich atmosphere promotes nitrogen atoms to bond to the rotors’ surfaces, hardening and strengthening them.
A revised brake apply system complements the new brakes with improved feelings of firmness and smoothness that give customers confidence when they step on the brake pedal. With it, an enhanced brake vacuum pump improves braking capability through greater brake system boost, while the brake pedal assembly itself is lighter, for a more uniform, linear feel throughout the entire pedal travel range.
In short, when the driver steps on the brake pedal, the response is firm, smooth and confidence-inspiring.
The SUVs also feature Auto Grade Braking, which uses engine and transmission controls to slow the vehicles on a long downgrade, helping maintain vehicle speed and reducing the need for the driver to use the brakes.
Electronic vehicle-control technologies
StabiliTrak electronic stability control system is standard on all models, and works in concert with the brake system to provide more precise and controlled ABS stops, greater traction and excellent cornering stability. It also incorporates rollover mitigation technology, which anticipates tip-up conditions – such as fishtailing – on a flat road surface and rapidly applies brake pressure to help reduce the likelihood of a rollover.
Trailer sway control is standard and works with StabiliTrak to provide an added measure of confidence when towing. It senses conditions of trailer sway and, without input from the driver, intervenes with braking and/or reduced engine power to bring the trailer under control and keep it on its intended path. The system will use electric trailer brakes when a trailer is plugged into the standard harness.
The SUVs also offer an integrated trailer brake controller and hill start assist, which making towing easier. The trailer brake controller allows the driver to adjust the amount of output available to the electric trailer brake and to manually apply the brakes, which is very useful with customers who use their truck regularly to tow loaded and empty trailers back to back.
With GMC’s standard hill start assist, the brakes hold for about 1.5 seconds on grades of 5 percent or greater when the driver takes his or her foot off the brake pedal, preventing rollback for a more confident take-off on hilly terrain – especially with a trailer.
GMC has manufactured trucks since 1902, with innovation and engineering excellence built into all GMC vehicles. The brand is evolving to offer more fuel-efficient trucks and crossovers, including the Terrain small SUV and Acadia crossover . GMC’s highest-volume vehicle, the Sierra pickup, is the most powerful light-duty pickup on the market, and the first full-size pickup to receive the highest-possible five-star Overall Vehicle Score for safety since the National Highway Traffic Safety Administration changed its New Car Assessment Program for the 2011 model year. Details on all GMC models are available at http://www.gmc.com/, on Twitter at @thisisgmc or at http://www.facebook.com/gmc.