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.