Just what is the 25% MPG improvment in GM's new Hybrid SUV offerings?

Several sources are reporting (ABG included) that GM will offer hybrid SUVs as soon as the 2008 Model year. Based on technology developed by a team consisting of GM, BMW, and Daimler Chrysler the models are expected to get 25 percent better fuel economy. In addition to the hybrid driveline, the 6.0 liter V8 engine will be able to deactivate half its cylinders during cruise. To save about 300 lbs (~140 kg) weight, both the Chevy Tahoe and GMC Yukon will have aluminum hoods and tailgates. Hence, engine, driveline and structure are involved in this fuel economy improvement program. The 2007 EPA Fuel Economy Test does not offer a 6.0 liter version of either the Tahoe or the Yukon. Largest engine is the 5.3. The 6.0 liter engine is available now in the Trailblazer. The "25 percent improvement" needs to be defined further as the new EPA Mileage tests will be in effect for the 2008 model year. EPA says: "EPA recently revised methods for estimating vehicle fuel economy to better represent current driving styles and conditions. The new methods-which apply to model year 2008 and later vehicles-include the city and highway tests used for previous models along with additional tests to represent:
  • Faster Speeds and Acceleration
  • Air Conditioner Use
  • Colder Outside Temperatures

MPG estimates will also be adjusted downward to account for factors that are difficult to replicate in a laboratory, such as wind and road surface resistance."

Is the 25 percent based on the old or new EPA estimates? Just the revised testing procedure will grab about 10 percent of that improvement, plus there is the extra weight and emissions of the larger engine. So these 2-mode hybrid SUVs may be 25 percent better, but starting from a lower EPA number than previously published. For a 3 MPG improvement over 12,000 miles at $3 a gallon and 17 MPG for a non-hybrid starting point, there is a saving of $ 318 a year. Hope this new hybrid package costs less then $2,000 for about a 6 year payback.

[Source: GM]

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