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The Chevy Tahoe Hybrid is as provocative and political a vehicle as you'll see this year. Why, it's practically a polemic. And those are just the "P's."

By way of a fantastic exertion of technology and human capital -- which I hereby honor and praise even as I question them as misallocated -- GM has managed to give one of its behemoth SUVs marginally better fuel economy. Here are the relevant data points: The two-mode hybrid Tahoe returns an EPA estimated fuel economy of 21 miles per gallon in the city, 22 mpg highway; the 4x4 version gets an even 20/20, city/highway. The company and its various choristers -- such as the Green Car Journal, which recently named the Tahoe Hybrid "Green Car of the Year" -- are pleased to point out that represents up to a 50% improvement of in-city fuel economy over the non-hybrid Tahoe.

The objectors have rebelled against the symbolism of the thing. It might be half-again better, but it's still an awful, blot-out-the-sun SUV. Isn't this like putting handlebar tassles on the wingtips of a 767 jet?

I had a chance to spend a couple of days in the Tahoe Hybrid; in fact, I believe the vehicle I drove was the same one that appeared on the show stand at the recent L.A. auto show -- white, with gold "Hybrid" decals along the scuppers. People have accused Prius owners of being ostentatiously green, but the badge-barnacled Tahoe Hybrid might as well have roof-mounted green emergency lights and a "Green Green!" whoop siren.

So, what's it like? For sheer execution, you can do nothing but throw rose petals at the thing. The engine starts instantly -- as you would too if you were goosed with a 300-volt battery pack -- and falls into a serene idle. Once the gas engine reaches operating temperature, it will shut down during low speed/load conditions, and if you feather the accelerator just right you can make the Tahoe Hybrid sluice along at up to 30 mph in all-electric mode, just a 5,700-pound Prius. The vehicle's two honking 60 kW traction motors (wrapped around the transmission) are primarily responsible for the uptick in around-town mileage.

As in Toyota's familiar hybrids, the gas engine looks for opportunities to shut itself down, such as when the vehicle is coasting, braking or stopped. Likewise, the system exploits the otherwise-lost kinetic energy of the drivetrain during coasting and braking, with the traction motors switching polarity to become generators, helping to pump up the traction battery.

GM has made a fair amount of bubbles calling it a "two-mode" system, though I'm not clear even now what the two modes are. I count three: electric only; gas only; and/or gas-electric, in which the operating system constantly ciphers the fuel-saving optimum between the engine's contribution and the electric motor's. If you wanted to send a congratulatory case of beer to anybody at GM, address it to the software writers -- whose ka-jillion lines of code keep the engine, transmission, batteries and motors in a constant state of reification. Spare a six-pack for the transmission's designers, for it is the transmission -- with its three planetary gearsets, two integrated motors (with their own reduction gears) and various other hardy fitments -- that allow the Tahoe to tow 6,200 pounds, a tonnage that would fatally herniate a Toyota Highlander Hybrid.

Put the power down and the 5,700-pound SUV goes like a rear-ended boxcar: The combined output of engine and motors is a romping 332 hp and 367 pound-feet of torque, much of it arriving with boot-in-the-pants authority in the low rpm range.

What's astonishing in even a cursory round-the-block test drive is the seamlessness, the absence of shudder or second-order vibrations, with which all this heavy-duty machinery goes about its business. I know Lexus makes big V8 hybrids, but we're talking a GM 6.0-liter V8 that comes on with all the drama of an indicator light.

Behind the wheel, the Tahoe Hybrid has the cues of a regular Tahoe, including a cabin the size of a handball court. Here and there are signs of a light-weighting program undertaken to counteract the added hardware and batteries: The upholstery is thinner and lighter (the second and third rows still fold flat into the cargo floor). The Hybrid makes use of loads of alloys, including lightweight wheels, aluminum hood and liftgate. Stretching the mileage a bit further, the Hybrid uses low-rolling resistance tires. These will not, I repeat, not get you over the Donner Pass in winter.

You want an astonishing number? The Hybrid's aerodynamic efficiency -- coefficient of drag -- is a slippery 0.34 Cd, compared to 0.39 Cd for the standard Tahoe. Not bad for a vehicle that looks like a refugee from the shipping yard at Long Beach.

Meanwhile, the Vortec V8 employs what GM calls active cylinder management -- other companies call it cylinder deactivation -- that chills out four cylinders when demand is light and reactivates them as demand increases. All of this has to play in a complex computer contrapuntal melody with the transmission, battery and motor controls. And all of it does.

So isn't this champagne-popping territory? Yes, no. . . . Could I ask some inconvenient questions?

First, what would the mileage of this vehicle be with all the improved aerodynamics, low-rolling resistance tires and aluminum body panels, yet without the fretful weight (and cost) of the hybrid system? What is the cost-benefit ratio of the hybrid system apart from these improvements? And shouldn't the improvements be standard issue?

It's hard to tell exactly what the "hybrid premium" is on the Tahoe Hybrid (MSRP of $50,490) but it looks to be, at a minimum, $8,000. That's a huge lump. One argument to celebrate this technology is that it could be mainstreamed into the hundreds of thousands of full-size trucks and SUVs GM sells. But how realistic is that? Does this super-low-volume program do more for corporate image than corporate average fuel economy?

What is this program's budget? How does it compare to GM's ad budget that crows about the program? The word is greenwashing.

Diesel?

Are we coming in at the middle of the play? Perhaps the problem with judging the Tahoe Hybrid harshly -- it does seem absurd on the face of it -- is that we don't know, or little appreciate, the larger plan at work. Perhaps GM means what it says when announcing that the company plans to electrify personal transportation, and has tackled the biggest challenge first: putting its most fuel-thirsty products on a gasoline diet. Could it be we're being cynical about a good-faith effort?

What really needs to be re-engineered, of course, is the consumer, who opts for these big, heavy-duty vehicles for personal transportation and light loading when smaller, lighter vehicles will do (I assure you, people, you don't need a Suburban to trailer your 300-pound dirt bikes). This is a contentious issue, since Americans feel they should be able to drive whatever they can afford, disregarding the fact that the sky -- and our collective debt of foreign oil -- is part of the public commons. The recent revision of CAFE standards helps, but there are plenty of people who regard any attempt to regulate the vehicle fleet as Kremlin-esque social engineering.

For now, we have this paradox, a fantastically fuel-efficient vehicle that's still a gas hog. A hybrid that's simultaneously good (promise) and bad (reality). Matters can only get more muddled when the Hybrid Hummer comes rolling out.

dan.neil@latimes.com

2008 Chevrolet Tahoe Hybrid Base price: $50,490Price, as tested: $55,000 (est.)Powertrain: Hybrid gas electric, 6.0-liter, 24-valve aluminum overhead-valve V8 with variable cylinder management and variable valve timing; continuously variable transmission; rear-wheel drive with locking rear differentialHorsepower: 332 at 5,100 rpmTorque: 367 pound-feet at 4,100 rpmCurb weight: 5,700 pounds (est.)0-60 mph: 9 secondsWheelbase: 116 inchesOverall length: 202 inchesEPA fuel economy: 21 miles per gallon city, 22 mpg highwayFinal thoughts: Chartreuse car of the year?

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