Diesel Audi Q7 TDI has power, elegance, but not much space

The Audi Q7 TDI is a recently launched diesel-power variant of the brand's popular (by Audi's low-volume standards) big SUV.TDI stands for turbocharging and direct injection of the fuel. Turbocharging lets an engine accelerate more quickly. Direct injection of the fuel improves power and cuts pollution. Programmed just so, as it apparently is in the Q7, direct injection can minimize a diesel's signature rocks-in-a-tin-can sound.Diesels can get 25% to 40% better mileage than similar-size gas engines. And diesel fuel, recently more expensive than gasoline, has just become cheaper. Easy to see the appeal.The diesel Q is $1,450 more than the V-6 gasoline model equipped the same. That's a modest premium. Gasoline versions of the Q7 were introduced in the U.S. in 2006 as '07 models.Here's what you might like about the TDI, on sale since late April:Power. Diesels have the low-speed torque that appeals to Americans because of our slug-and-chug driving conditions. The test vehicle moved smartly off the line from a dead stop, and once the turbo kicked in fully (all passenger diesels are turbocharged nowadays), it hurtled relentlessly.Smoothness. The automatic transmission shifted commendably up or down under any circumstances. It had a manual-shift mode, but in a low-revving diesel, that's borderline irrelevant.The ride was firm but not harsh. Controls operated with the ease and feel expected in a luxury vehicle.Appearance. Generally well-drawn and elegantly executed. It would be news if an Audi were otherwise nowadays. As they say in showbiz, don't go changin'. Reasonable people often disagree on matters of taste, though.TDI looks very much like the gasoline versions that have been on the road three years, but the test vehicle still got a remarkable number of appreciative scans by other motorists, even in neighborhoods where Q7's are commonplace. Hard to explain.Highway mileage. That's where diesels shine. Q7 TDI is rated 25 miles per gallon. Audi says it got 33 in a so-called mileage marathon last year. Several teams drove 4,887 miles cross-country, and 33 mpg was the top average. The average of all teams' averages was 27 mpg.Handling. Surefooted for a 3-ton SUV, which is not the same as saying it handled like a sports sedan, which it didn't.Details. In windows-down mode, no buffeting, just breeze. Many automakers fail that test.Second-row reading lights' tightly aimed beams didn't distract the driver at night. Another useful feature done poorly by most car companies.Power tailgate had an array of height adjustments, from wide open to accommodate tall folks down to a height that works in low-ceiling garages.Robustness. The solid feel you'd expect in a German brand (though all Qs are made in Slovakia, mainly of Hungarian parts).All those things made the TDI a sweetheart from the driver's seat. And, a bonus, despite its full-size SUV footprint, it wasn't intimidating in tight spots nor difficult to park.Where? Made in Bratislava, Slovakia, with Hungarian engine, Japanese transmission.Why? Audi sees a future here for diesel because of fuel-economy benefits and low-pollution tuning.How much? Starts at $51,725 including $825 shipping. Audi says buyers might qualify for $1,150 federal tax credit. Lavish test vehicle: $62,375.How powerful? Typical diesel: Modest horsepower, big torque. 3-liter diesel V-6 rated 225 hp at 3,750 rpm, 406 pounds-feet of torque at 1,750 rpm, teamed with six-speed automatic transmission with manual-shift mode and quattro all-wheel drive.How big? Lower roofline than Chevrolet Tahoe truck-based SUV or GMC Acadia crossover SUV, otherwise very close in size, but the Audi has less space.Q7 is 200 inches long, 78.1 in. wide, 68.4 in. tall on a 118.2-in. wheelbase. Weighs 5,512 lbs.Passenger space: 133.2 cubic feet. Cargo: 10.9 cu. ft. behind third row, 42 cu. ft. when third row's folded, 72.5 cu. ft. with second and third row folded.How thirsty? Rated 17 miles per gallon in town, 25 highway, 20 mpg (5 gallons per 100 miles) in combined driving. Trip computer in test vehicle showed 15.7 mpg (6.37 gallons per 100 miles) in easy-going suburban driving.Burns ultralow-sulfur diesel fuel, holds 26.5 gallons. Audi says accessory tanks hold 10,000-mile supply of AdBlue, a urea additive needed by most diesels to meet clean-air rules.Overall:Powerful, classy; annoyingly complicated controls, disappointing space.