2008 Chevrolet Tahoe Hybrid Review

Specifications

GM Looks to Hybrid Technology to Reinvigorate Big SUV Sales 

Patience will be required, but soon enough Chevy will deliver a full-size SUV capable of pint-size SUV fuel economy; and isnt that a contradiction in terms? Perhaps so, but definitely a most welcome contradiction thanks to the bowtie brands claim of a 25 percent boost in the composite fuel efficiency of a V8-powered Tahoe when GMs two-mode full hybrid technology and its advanced Active Fuel Management technology are both applied.

GMs Active Fuel Management (AFM) technology, known previously as Displacement on Demand (DoD), deactivates four of the engines eight cylinders when the need for output is low, resulting in less fuel burned, money saved and emissions reduced. Theres nothing particularly new or groundbreaking about this technology, which, in various forms, is currently in use by GM, Chrysler and Honda. Marrying AFM with a two-mode, full hybrid system is, however, the latest in fuel conservation science. Hondas new Accord Hybrid incorporates a mild-hybrid system with its cylinder-deactivated V6, mind you, so working the two technologies in tandem isnt an entirely new concept. And while GMs two-mode full hybrid system has been in-use in transit buses, it has not been applied to their car and light truck divisions as of yet.

The two-mode full hybrid system in question is currently being developed by GM, along with partners BMW and DaimlerChrysler, with the intent on making it capable of running on gasoline or diesel, for use in private vehicles in both North America and fuel-starved Europe. Reduced fuel consumption equals fewer hydrocarbons and less exhaust emissions, which will also help auto manufacturers meet tightening emissions regulations for diesel-powered vehicles.

The two-mode hybrid system under development is intended to optimize both highway and city fuel efficiency, with the first mode engineered to address slow moving traffic patterns. It enables the vehicle to operate in any one of three ways: electric power only, engine power only or any combination of the two power sources. Maximum benefit is naturally derived from electric power propulsion operating alone, allowing fossil-fuel-free movement in stop and go bumper-to-bumper traffic, until the engine cuts-in to recharge the 300-volt battery pack or hustle the Tahoe away with greater urgency.

It should be noted that even the first Toyota Prius featured a full hybrid powertrain, a setup that continues forward with every new Toyota and Lexus hybrid the automaker builds. Ford also has engineered its Escape Hybrid with a full-hybrid system, while Hondas have always been less expensive engine-assisted mild hybrids, that is, until the most recent 2006 Civic Hybrid was introduced this fall. Hondas change from mild- to full-hybrid systems is a significant move, now supported by GMs move from its Chevy Silverado and GMC Sierra hybrids, currently available, which are engine-assisted mild hybrids, to this new, more sophisticated powertrain introduced in the upcoming Chevy Tahoe Hybrid on Friday, January 8, at the North American International Auto Show in Detroit.

The second of the two modes incorporates sophisticated electronic controls, such as active fuel management, cam phasing, and late intake valve closure to increase the engines efficiency when its working in partnership with the electrical power source or operating independent of it. GM states that the shifts between the two hybrid modes are synchronous, which means no engine speed changes are necessary for the mode shift to occur, resulting in ultra smooth acceleration.

An interesting design aspect of GMs two-mode hybrid system is the integration of powerful compact electric motors engineered to fit within the space allotted a conventional automatic transmission. Both the engine and the electric motors transfer torque to a series of gears inside the Tahoes sophisticated transmission, which multiplies the incoming torque to propel the heavy vehicle. But unlike more typical continuously variable transmissions, GMs example uses no mechanical belts or bands to continuously feed torque to the wheels.

Although GM has yet to provide specifications and performance data for the upcoming two-mode full hybrid Tahoe, Mark Cieslak, assistant vehicle chief engineer for the hybrid project had this to say about the vehicle: “We took the brand-new, next-generation full-size truck platform, which already had segment-leading fuel economy and world-class aerodynamics, and took it to the next level. This was in addition to maintaining important performance attributes of full-size trucks, such as off-road capability, towing at 6,000 pounds, great 0-60 times and much more.”

I recently joined General Motors in Arizona for the launch of the all-new 2007 conventionally-powered Tahoe, featuring the brands 5.3-liter (327 cu-in), 4th generation small-block V8, which will also be used in the upcoming hybrid edition. Chevy placed much emphasis on the efficiency of this mill, which EPA ratings confirm will return 15 mpg in the city and 21 mpg on the highway respectively. Such class-leading fuel economy is in part attributable to GMs Active Fuel Management technology. Adding the proposed two-mode full hybrid system to this already stingy Vortec V8 is bound to launch it into uncharted fuel-efficiency territory, at least among full-size sport utilities.

Of course, it should be noted that Chrysler Group, which shares in the dual-mode fully hybrid technology used by GM in this Tahoe, will be incorporating it into its large SUV lineup, which we have just learned will increase in size thanks to the Durango-based Aspen SUV expected in production trim later this year. Most likely, the Aspen hybrid, and other hybrid versions of Dodge and Jeep models, will arrive around the same time as the fuel efficient Tahoe Hybrid, and also take advantage of cylinder-deactivation technology. Trumping both GM and DaimlerChrysler will most likely be Ford and Toyota, which are expected to develop versions of their full hybrid systems for their larger, V8-powered SUVs. Neither rival currently offers cylinder-deactivation, mind you, but the technology is likely in the works.

But for the time being, its difficult to think of a vehicle more deserving of huge strides in fuel economy than GMs new Tahoe. I was very impressed with its styling, build quality and operational refinement. GM has done a remarkable job of taking the venerable full-size SUV up-market. It now imparts a premium feel and look completely beyond anything the Detroit-based automaker has done before, at least with its full-size truck platform. A smooth shell, tight panel gapping and the integration of a full front fascia has netted the big mover a co-efficient of drag equal to the 1992 through 1996 Corvette - and we all know that reduced air turbulence translates into great aerodynamics, which reduce fuel consumption, as well as less wind noise. In keeping with the Tahoes heightened state of serenity, engineers also managed to reduce road noise transmitted through the Tahoes newly improved chassis.

Inside, the new Tahoe awaits a beautifully constructed cabin, full of space, opulence and high quality materials and surfaces. Look for what may be the most attractive instrument panel in the business, to incorporate a few high-tech goodies when it gets transformed into hybrid guise. The new gauge cluster sits approximately 6 inches lower and further forward than in past Tahoes. Unique convenience features include the segments first power-articulated fold and tumble second row seats, along with removable third row seating. A power-operated rear lift gate adds to the vehicles convenience.

In redesigning the Tahoe, ride comfort and handling were held as priorities for the body-on-frame, Texas-built rig. Its independent coil-over-shock front suspension and five-link rear coil setup performed marvelously over city pavement and mountain goat trails alike. The ride was absorbent and forgiving while never mushy or sloppy. In fact, hammering the SUV over severe washboard surfaces, common on dirt roads, failed to upset the apple cart, so to speak, even when pushing hard through turns. Yes, some oversteer was induced by these circumstances, but that was to be expected, and to the Tahoes credit, easily dealt with. When things got too hairy, GMs StabiliTrak stability control system with rollover mitigation stepped in to defuse the tension. No doubt, the new Tahoe Hybrid will include such safety systems.

StabiliTrak, along with dual-stage front airbags, are carried as standard equipment on the non-hybrid 2007 Tahoe, while roof-mounted head curtain side-airbags at all outboard-seating positions are optional. Standard in the braking department is a full set of antilock disc brakes that performed admirably, clawing the Tahoes mass back from 60 mph to zero with stunning brevity during which vehicle control was never an issue. With such gallant driving dynamics and impressive versatility, extending the distance a liter of fuel will carry the Tahoe - and by virtue reducing its emission of harmful pollutants - is a very positive step forward indeed, and might be what keeps this very practical full-size SUV segment alive.

And to ensure the two-mode full hybrid Tahoe projects a distinctive image to complement its cutting-edge powertrain and superior fuel economy, Design Manager David Smith and his team lowered it by 0.4 inches in the front and incorporated additional aerodynamic features to magnify its contrast against the non-hybrid Tahoe. Prominent hybrid badges to complete the look, which I rate as the sharpest in the full-size SUV segment.

But in order to sell a full-size hybrid SUV, Chevy will have to rely on more than just good looks. The technologies at work in the 2008 Tahoe Hybrid are very complex and sophisticated, which is why potential customers will look long and hard at the warranty coverage provided by GM, as well as any available reliability data. They will also sharpen their pencils and do the math; will it make financial sense to spend the extra dough to save money on fuel expenses? Pricing has not been announced yet, so guess work is at play here, but generally speaking it takes a lot of driving or a money-be-damned commitment to the environment to make the added expense of hybrid ownership truly profitable. Only Hondas new Civic, which recently dropped in price by thousands in base trim while upping every aspect of its design, build execution and performance, seems like a decent bet financially. Assuming Chevy gets the numbers game right (warranty, price, reliability), the 2008 two-mode full-hybrid Tahoe may well be the SUV of the future; and I hope thats the case.

The Tahoe Hybrid is expected to hit the market next year as a 2008 model, along with its two-mode hybrid GMC Yukon cousin. Also, expect more derivatives among full- and mid-size GM SUVs to follow, as well as new versions of the automakers full-size pickups to feature its dual-mode full hybrid technology. Pricing and production volumes of the Tahoe Hybrid have not been announced by GM, but can be expected closer to its launch date.