Consumer Guide's auto editors are adding a new dimension to our extended-use test program. For half of the 2007 Chevrolet Tahoe's 12-month stay, we will operate it on E85 ethanol fuel. Our goal is to determine what effect ethanol has on fuel economy and engine performance versus conventional gasoline.

Why Test E85?

Domestic automakers, and General Motors in particular, are heavily promoting the use of E85 as a means for America to achieve energy independence. E85 consists of 85 percent ethanol alcohol, refined primarily from corn, and 15 percent gasoline. GM claims this alternative fuel offers the same performance as conventional gasoline, but is good for the environment because it creates fewer exhaust emissions. It's also cheaper per gallon than regular fuel thanks to tax credits and government subsidies.

More on E85

Flex-Fuel

The Corn Belt is where you'll find most E85 filling stations right now. Minnesota has the most with about 300. Illinois follows with about 130. More are being added, both in the Midwest and around the country. Florida recently opened its first E85 pump. Louisiana, Alabama, and several northeastern states currently have no stations offering E85.

E85-capable engines require the installation of an additional sensor to detect the ethanol/gasoline ratio in the fuel tank. As ethanol is a corrosive liquid, E85 vehicles require modifications to fuel delivery components, including a stainless steel fuel tank and Teflon-coated fuel lines. Automakers typically put special badging on E85 vehicles. Our extended-use Tahoe has a "Flex-fuel" sticker on the tailgate, as well as a yellow gas cap, signifying E85's connection to corn.

The National Ethanol Vehicle Coalition, a non-profit advocacy group, maintains a comprehensive nationwide database of E85 fueling stations online at http://www.e85refueling.com.
When we asked GM for one of its redesigned large SUVs, taking a long-term look at E85 was a primary goal. The promise of reduced emissions, similar engine performance, and the "feel good" quotient of using domestically produced fuel looked good on paper. We do have some concerns, though. Currently, E85 availability is very limited outside the Midwest. There's also the potential for reduced fuel economy because though E85 produces fewer exhaust emissions than conventional gasoline, it doesn't burn as efficiently. One gallon of E85 generates only 72 percent of the energy of a gallon of gas, which theoretically means fuel economy drops by 28 percent. Our extended-use evaluation will put this assertion to the test.

The EPA rates our four-wheel-drive Tahoe at 15 mpg city/21 highway on regular gasoline. Ratings drop to 11 city/15 highway for E85. That's more than a 25 percent drop in estimated fuel economy for both city and highway. But E85 is cheaper, right? At the time you read this, regular-grade gasoline is about $2.50 per gallon around our suburban Chicago office. E85 at the same station sells for about $2.15, for a difference of 14 percent. Suddenly E85 doesn't look so attractive where it will likely matter to consumers the most--the bottom line.

However, we're going to reserve judgment until the end of our test. Our evaluation will run the Tahoe for its first three months on conventional gasoline. We'll then switch to E85 before winter sets in, and then alternate with regular gas every three months for the rest of its time with us.

About the Tahoe

Tahoe is completely redesigned for 2007, and it couldn't have come at a better time for GM. Large SUVs are typically an automaker's most profitable vehicles, so GM needs Tahoe to be a sales success in order to reverse the company's financial losses and shrinking market share.

GM went for broke in developing the '07 Tahoe. At its foundation is a completely new platform internally dubbed GMT-900. Tahoe received it first, followed in short order by GM's other large SUVs: GMC Yukon and Cadillac Escalade. The redesigned Chevrolet Silverado and GMC Sierra large pickup trucks will get this platform when they go on sale this winter.

Safety and Powertrain

Our test Tahoe is a top-of-the-line four-wheel-drive LTZ model, equipped with just about every available option. The 4WD system is GM's Autotrac, which allows it to be left engaged on any road surface. It also has a low-range gear for severe weather or off-road conditions. Other safety features include ABS, GM's Stabilitrak antiskid system with traction control, front side airbags, and curtain side airbags that cover all seating rows and include a sensor designed to deploy them in the event of a rollover crash.

Under the hood is GM's workhorse 5.3-liter V8 engine, which produces 320 horsepower. In addition to E85 capability, this engine has GM's Active Fuel Management system, which shuts off four cylinders under cruise conditions to save fuel.

Chevrolet Tahoe E85
In its first 1805 miles, our test Tahoe has been trouble free and is averaging 14.2 mpg on conventional gasoline.
A four-speed automatic transmission is standard, and it seems like a relic among other vehicles that offer five- and six-speed automatics. For the most part, the transmission gets the job done. We have praised GM automatic transmissions for their prompt, smooth shifts, but one editor who has spent a lot of time with our extended-use Tahoe is noticing some delayed downshifts. This is something we'll keep an eye on as we accumulate more miles.

LTZ Tahoes have standard 20-inch tires versus the 17s found on base versions. While we laud the carlike ride quality on the base tires, our extended-use model's 20s transmit more bumps into the cabin. It's not a huge demerit, but we recommend you try before you buy. The steering and handling of our Tahoe is also praiseworthy. The redone suspension and steering components address the sloppy feel of GM's previous-generation GM large SUVs. It's no sport sedan, but it's as solid as you can expect from a vehicle that's nearly 17-feet long, 6.5-feet tall, and weighs more than 5500 lbs.

Creature Comforts

On the luxury side, our tester has leather upholstery with heated front and second-row seats, a 12-way power driver seat, six-disc CD changer with MP3 CD support, satellite radio, rear DVD entertainment, and a navigation system. We like Tahoe's modern interior design. Most interior materials feel high-class, and our tester has excellent panel fit and finish. The overall cabin atmosphere is a big step forward from the previous generation, which had an overabundance of dull, hard plastic surfaces.

Passenger room and comfort in the first two seating rows are also pluses of the '07 Tahoe. The bucket seats are comfortable and offer occupants generous head and leg room. We're less enthused about the third-row seat. Even medium-size adults are cramped for leg room, and the bench seat is uncomfortable for all but short trips. At least getting back to the third row isn't terribly difficult thanks to our tester's power flip-and-fold second-row seats. A toggle switch on the overhead console powers each seat down and forward, though they have to be returned upright manually.

GM's large SUVs are extremely pleasant and capable vehicles. Tahoe and its GMC Yukon sibling are Consumer Guide Best Buy choices in our large-SUV class, and the upscale Cadillac Escalade is a Best Buy among premium large SUVs. Our extended-use Tahoe rears its head into premium territory with an as-tested prices of $53,455. With less lavish equipment, prices go down into the mid $40s.

Initial Thoughts

In its first 1805 miles, our Tahoe has been trouble free and is averaging 14.2 mpg on conventional gasoline. Until we get some concrete performance and economy numbers with E85, the jury's still out on this alternative fuel. But we can give kudos to GM for giving shoppers an option to use E85 if they so choose.