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2008 GMC Yukon Hybrid 4X4 Road Test

If it weren't for the big Hybrid badges that have been plastered all over the

You can't tow or haul anything serious with a hybrid... until now. (Photo: Justin Couture, American Auto Press)

rocker panels and the glass, people wouldn't have the faintest idea that the new GMC Yukon Hybrid is more than just a regular, full-size sport utility vehicle. It doesn't take long to see the effects of the big, italicized block lettering - just keep an eye out for other drivers. Motoring down the road the driver of a silver Prius looked up at the big, burgundy Yukon with disapproval, the driver rolling her eyes only to see the hybrid badges, then smiled and waved as if I were a member of some virtuous hybrid club. Believe me, it's a shocking thing.

Admittedly, people aren't going to focus in on the fact that the Yukon Hybrid has unique bumpers and a flush underbody to help it generate a remarkably low 0.34 coefficient of drag. They aren't going to be looking out for the little green "H" that creatively incorporates a printed pattern of a circuit board as a background. No, they're looking at the size of the vehicle and its specifications, which, admittedly aren't encouraging. You get a rather big 6.0-liter V8, and, when combined with the electric assist, it makes 332 horsepower and 367 lb-ft of torque, plus it rides on a body on frame structure that was designed to haul 22'

Decals let the world know that you aren't out to destroy it. (Photo: Justin Couture, American Auto Press)

speedboats. But then you get into the caveats. It's got an idle-stop system so it shuts off at red lights and AFM so it shut down four cylinders under light loads. And even better news is that because the electrical assist from the battery system helps to boost things along, the Yukon is more likely to run on four cylinders for a greater portion of the time.

For the most part the Yukon Hybrid works like a regular full hybrid vehicle like a Prius or an Escape Hybrid. Power from the gasoline side of the equation and power from the electrical side are combined, sent to the CVT (or more precisely the electronically variable transmission), through the transfer case (on 4WD models) and then to the drive wheels, with the ability to cruise purely on electricity factored in. In the city and at lower speeds and loads, this is what the Yukon will do. Because the battery pack has been hidden under the floor, there's no compromise on interior space or volume either.

Aerodynamics and weight reduction - what works for sports cars works for big body on frame SUVs too. (Photo: Justin Couture, American Auto Press)

The problem is that hybrids don't like heavy loads associated with towing or cruising on the highway. And that's where the Yukon, specifically its 2 Mode system differs from its peers. You see, inside that transmission tunnel isn't just a CVT - the housing of the standard Hydramatic transmission also stores a pair of 60 kW electric motors and actuators. When higher loads are put on the Yukon 2 Mode, it swaps into the second mode that's mostly gasoline-based, and uses four fixed ratios like an automatic transmission that mostly bypass the electric motors for greater efficiency. If you need a little extra oomph the electric motors can (and will) kick in, but for the most part it's the V8 engine flexing its muscles. It doesn't sound like much, but this is what allows the Yukon to function as an eight-seater, 6,200 lb towing machine. Nothing less would have made the cut.

Playing a supporting role to the batteries, electric motors and so on is a strict weight loss program. The components that make up a hybrid are heavy - really heavy. What's amazing is how much GM has managed to pare off of

Just as comfy and civilized as before; it's quieter too. (Photo: Justin Couture, American Auto Press)

the Hybrid's curb weight, as the mass difference between a regular Yukon and this eco model is more than nominal. That's 400 lbs they've managed to strip out, by the way, especially impressive since it still has all the luxuries and goodies, not to mention it's quieter than the standard truck. They've done it by replacing the wheels, which despite being 19 inches across weigh 5 lbs less apiece. The hood's aluminum and the front seats are thinner and lighter. And it's not lighter because they've stripped out 220 lbs worth of insulation either; by switching components like the air conditioner compressor and power steering to electric units, GM has quieted things down significantly.

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