Let's get something out of the way right now. Not every vehicle we write about here is going to be as efficient as a Prius or have a plug or require pedal power. There is a huge market place of vehicles out there. None of those vehicles are for everyone. Not everyone needs or wants a Prius or a Mitsubishi iMiEV or a Chevrolet Silverado. However, in spite of rapidly falling sales of big trucks there is still a very significant need out there for such vehicles. I am in no way advocating (nor have I ever done so, in fact for many years I have done the opposite) that people should buy a Silverado or other truck for personal transportation or commuting. Having said all that, these vehicles and others all need to become more fuel efficient, for economic and environmental reasons. In a market segment that will still amount to about 1.5 million vehicles in the U.S. this year, GM is scaling back production but they are still trying to make the vehicles they sell more efficient. To that end they are introducing the both XFE and two-mode hybrid variants of the GMC Sierra and Chevy Silverado for the 2009 model year. We had a chance to sample both versions on a brief drive this week and you can read about it after the jump.


Photos Copyright ©2008 Sam Abuelsamid / Weblogs, Inc.

So what's the scoop on these updated pickup trucks? Frankly there are no huge surprises. The hybrids were announced long ago. GM declared they would build the Silverado hybrid last November at the LA Auto Show just as production was starting on the Tahoe and Yukon hybrids and the Sierra was first seen at the Chicago show in February. Since the big pickups and the big SUVs share the same GMT900 architecture and the same conventional powertrains, it should be no surprise that they share the same hybrid hardware.

Just as in the SUVs, there is a 6.0L V8 bolted up to a Two-Mode hybrid transmission and a 300V nickel metal hydride battery pack under the rear seat. The V8 is still equipped with active fuel management (AFM, which is GM-speak for cylinder deactivation). AFM is also present on non-hybrid trucks, but when electric motors are present, the engine management system tends to keep the internal combustion part operating on only four cylinders during light transient maneuvers where it would otherwise operate on all cylinders. The additional torque required to maintain speed up a grade or during a passing maneuver is instead provided by the motors.



During periods of velocity reduction, the motors are driven by the wheels to charge the lump under the second row seat and driver braking demand is monitored by the electronics. If regenerative braking is available, the hydraulic brake pressure is reduced in conjunction with the amount of regen being done, providing total braking in proportion to what the driver is requesting through the brake pedal. Just as on the Tahoe, Yukon and Escalade, the new brake system gives the hybrid pickups a much firmer pedal feel without any of the sponginess typical of past GM trucks.

One element that will be common to both the XFE and hybrid pickups is the aerodynamic and suspension changes. While GM isn't going as far as they did with the changes to the hybrid SUVS, the pickups get a deeper full width front air-dam and a standard tonneau cover on the bed. They also get a re-tuned suspension that lowers the ride height slightly and thus the frontal area. GM claims a best-in-class drag coefficient of 0.412 for these trucks. That number is not bad for this type of vehicle but certainly nothing to write home about.



The hybrid pickups will get the same EPA mileage ratings as their SUV-bodied counterparts. The rear drive models get 21 city/22 hwy while the 4X4s get 20/20 ratings. The regular 5.3L RWD pickups get just 14/20 mpg. The pickups get a trailer tow rating of 100 lbs less than the SUVs, 6,100 lbs for the rear driver and 5,900 lbs if all wheels are driven.

The XFE designation will be available on both the pickups and SUVs starting this fall and just like on the little Cobalt it means Xtra Fuel Economy. Besides the aero tweaks, the XFEs also get some weight reduction and powertrain changes. Aluminum for the main and spare wheels is joined by an aluminum block for the 5.3L V8. All of the aluminum adds up to a 150 lb mass reduction which drops the XFE into the next lower EPA test weight class. All the XFEs have the 5.3 paired up with a new 6-speed automatic transmission and a taller 3.08:1 final drive ratio. The regular 5.3L trucks get a 3.42:1 final drive. The 5.3 in the XFEs gets the AFM system and the ability to run on E85 if the driver can find some.

On the road the XFE felt more than powerful enough and still has plenty of towing capacity for most people's needs. While the hybrid trucks benefit from significant noise reduction efforts in order to minimize the difference between engine on and electric drive modes, the XFE engine has more aggressive growl to its exhaust note. All the changes GM made only yield 1 mpg extra on both the city and highway mileage numbers, now at 15 city/21 highway. The tow ratings for the XFE pickups actually goes up from 6,600 lbs to 7,000 lbs. That just goes to show the difficulty of getting significantly improved mileage out of these types of vehicles.

In the future, the mileage of vehicles like this will improve further. They'll probably never reach 40 mpg, at least not with the capabilities that these trucks have. As fuel prices keep rising, people will continue re-evaluating their real needs in vehicles. The full size truck segment peaked at over 2.5 million units in 2004 and 2005. GM VP for full-size trucks, Gary White, projects 2008 sales at about 1.5 million but wouldn't say how low the segment would ultimately go. Trucks will ultimately end up going back to the original market they had, primarily commercial and fleet sales. That's why GM, Ford, Chrysler, Toyota and Nissan are all closing or re-tooling truck factories. This segment won't disappear completely, but it will continue to evolve. These trucks are a step in that direction.


Photos Copyright ©2008 Sam Abuelsamid / Weblogs, Inc.

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