Car and truck manufacturers have a habit of making improvements from the outside in. General Motors broke that habit with the 2011 Chevrolet and GMC Silverado and Sierra HD trucks by offering a long list of foundational technical improvements without many visual ones. On the outside, the '11 HDs get little more than a grille change and minor styling upgrades that you have to look at twice to notice. But what's newsworthy about the new HDs is what's lurking beneath the sheetmetal.?>
We were invited to spend a couple of days in the hills of Maryland, Pennsylvania and West Virginia to use the '11 HD Chevrolets and GMCs as you might: Loaded to the gills. Some of the trucks were carrying payloads of 1,800 or 3,000 pounds. Others were hitched to conventional camp trailers weighing over 9,000 pounds. One lugged a 12,800-pound fifth-wheel horse trailer. Another had 10,500 pounds of equipment trailer and skid steer hooked up.
The major technical changes start skeletally. The HDs get a completely new, fully boxed chassis that's much stiffer torsionally than the '10s, and the upgrade allowed for a complete redo of the suspension. Though the IFS is similar in general design to the previous SLA (Short/Long Arm) system, the components are all new and heavily beefed up. The upper control arms are now forged steel, with the lowers of cast iron. There are now five torsion-bar rates, fitted according to the rated front Gross Axle Weight Rating (GAWR) of the truck. The maximum front GAWR has increased 25 percent from a previous maximum of 4,860 pounds to 6,000 pounds-something that will make the snowplow crowd happy. The steering system was revamped, with a considerably faster steering box ratio that delivers better road feel and fewer turns lock-to-lock, all with no increase in steering effort.?>
Gone is the long-running two-piece front diff housing, replaced by a one-piece Salisbury design that is 7-percent stronger. Additional front drivetrain strength was gained with improvements in the CV axles, which were upgraded from six- to eight-bolt inner flanges, and the outer stubs are larger for a 22-percent improvement in strength. The brakes grew substantially, from 12.9-inch discs to whopping 14-inchers at both ends.
The rear axle and suspension weren't ignored, with the GAWR of the AAM 11.5-inch axle rising from 8,200 to 9,750 pounds by upgrading the axle tubes from 3.5- to 4-inch diameters. Axletube diameter was increased 11 percent in the diesel-powered trucks. The rear springs were upgraded from 2.5- to 3-inch width and are asymmetrical (meaning the axle mounts forward of the spring center). This reduces spring wrap, both empty and loaded. The diesel trucks come only with a 3.73:1 axle ratios, but the gassers have a 4.10:1 option.?>
The proven Duramax engine, an $8,395 option, picks up a boodle of power and torque for 2011. It goes from 365 to 397 horsepower and from 660 lb-ft to 765 lb-ft. According to Gary Arvin, the Duramax Diesel Chief Engineer, there's room to grow from there. The Duramax's Allison 1000 trans is still a six-speed, but the internals have been heavily revised to deliver a commercial-grade duty cycle without the commercial-grade "neck-snapper" shifts.
The standard engine for the HD is the still silky 6.0L flex-fuel Vortec V8. Yeah, it's riding on the coattails of last year's upgrades, cranking out 360 horsepower and 380 lb-ft, but that's a good thing. It's a potent, economical engine and more than enough for a 3/4-ton or 1-ton truck. Its superb performance is why we don't miss the old 8.1L big-block any more than we do. Several of the trucks at the event had 6.0L V-8s and they had plenty of go, whether loaded or unloaded. It's matched well with the 6L90 six-speed automatic that has a nice, deep 4.03:1 first gear.
The news accompanying all the technical renovations was the increase in work capacity. Using the popular Crew Cab diesel (SRW) as an example, the maximum 2500HD GVW has jumped from 9,200 to 10,000 pounds (2,523- to 3,125-pound payload), with a GCVW bumped from 23,500 to 24,500 pounds. The 3500HDs go from a 9,900-pound GVW to 11,600 pounds, and the payload jumps from 2,933 to 4,165 pounds. The GCVW remains the same as the 2500HDs.?>
Reading the technical nitty-gritty is one thing, but experiencing how they translate to a driving experience is another thing altogether. You'll first notice the uprated diesel's truly "yeehah" performance, empty or loaded. It's stunning how fast these trucks could take a 9,300-pound load to 60 mph going uphill against a 6-percent grade. On 5- to 7-percent grades with that load, the truck cruised at the speed limit in top gear and with the converter locked. With the multifunction info center button set to read "Trans Temp," we didn't see much more than about 165 degrees with the Allison and just under 200 with the 6L90 on the gas trucks, showing GM has tight control of transmission oil temps under load. The truck's ride and handling, both loaded and unloaded, is definitely in the outstanding category for it class.
Even more impressive was how the exhaust brake and Grade Braking features worked, even in cruise control. The exhaust brake system is activated by a button on the dash and uses the variable-geometry vanes on the turbo impeller to restrict the air flowing out of the engine. Full engagement is limited to when the throttle pedal is at zero and the torque converter is locked. It will block the exhaust right to the limit of the turbine's inlet pressure maximum.
The Grade Braking feature works with or without the exhaust brake activated. The TCM (Transmission Control Module) can sense a grade and uses the transmission to slow the truck. Apply the brakes on a grade, and the Grade Braking software takes over and automatically drops down a gear or two while keeping the converter locked.?>
Grade braking and the exhaust brake get even more aggressive in Tow/Haul mode. Both systems will integrate with the cruise control to automatically maintain the selected speed-even with a heavy load. On top of all this, there is a mode button on the shifter to manually shift the trans. All in all, this setup is a control freak's dream, and the systems work together almost seamlessly.
As impressed as we were with the stellar performance of the new HD GM trucks, we have a gripe. Overall, GM could improve the control layouts and ergonomics. Especially at the upper end of the options food chain, these trucks have a dazzling array of driver-controlled gizmos that can lead to confusion and distracted driving. With this many driver input options, the type and layout of these controls becomes vital. GM knows well how to do this, and when these trucks are refreshed cosmetically, it's seems likely they will improve the situation. We'd also like to see a power feature for extending the mirrors for towing.
Minor gripes aside, our impressions of the trucks after two day test could be described with two words-consummate performance. The truck leaves you with the impression it's never really working up much of a sweat. The NVH is under tight control and the ride is at the top of the class. GM didn't introduce a lot of show for the 2011 HDs, but they sure delivered a bunch of go.
Viscerally potent 400hp Duramax, exhaust brake and Grade Braking systems, substantially higher payload and tow ratings.
Control system layouts need simplification and integration.
Consummate, pack-leading truck performance.
- Vehicle/Model: 2011 GMC Sierra HD 2500HD Crew Cab SLT
- Base Price: $44,560
- Engine(s): 6.0L Vortec OHV V8 (std), 6.6L Duramax V-8 diesel (opt)
- Transmission(s): 6-spd 6L90 automatic (std), 6-spd Allison 1000 (opt w/diesel)
- Transfer case: Part-time 2-spd, MP1626 (electric-shift) or MP1226 (manual-shift)
- Low range ratio: 2.68:1
- Frame type: Ladder, fully boxed
- Suspension, f/r: independent SLA, torsion bars/asymmetrical, variable-rate leaf springs
- Ring and pinion: 3.73:1 (std, 4.10 optional w/6.0L)
- Max crawl ratio: 30.98:1 (diesel), 40.28:1 (gas, 3.73)
- Steering: Power, recirculating ball
- Brakes: 13.97x1.57 discs
- Wheels: 17x7.5, steel or alloy, 20x8.5 alloy opt. (others optional)
- Tires: LT265/70R17 or LT265/60R20 all-terrain (others optional)
- Wheelbase (in): 153.7 (shortbox), 167.7 (longbox)
- Length (in): 240.1 (shortbox), 259 (longbox)
- Height (in): 78.3
- GVWR (lb): 10,000
- Base curb weight (lb): 7,208 (shortbox), 7,387 (longbox)
- Max towing capacity (lb): 13,000 (ball hitch), 15,600 (fifth-wheel)
- Fuel Capacity (gal): 36