The story is the same inside, where it’s standard A5 all the way. As you’d expect from an Audi, the seats are comfortably firm, the fit and finish are excellent, and the overall design exudes understated sportiness.
Note, however, that the CNG tanks cut trunk space from 16.9 to 13.8 cubic feet.
A second fuel gauge for the CNG tanks replaces the temperature gauge normally found at the left side of the instrument cluster. An icon in the instrument cluster tells the driver if the engine is running on CNG, gasoline, or both.
When the CNG tank is empty, the engine-management software automatically switches to gasoline.
While the g-tron isn’t the least powerful car in the European A5 lineup, its power-to-weight ratio is one of the worst. We never assumed it would keep up with a RS 5, but on the road, it’s noticeably slower than the gasoline-only 2.0-liter version.
Acceleration remains brisk, and the engine is surprisingly eager to explore the top half of its rev range—meaning the A5’s performance genes are muted but still dominant.
The only signals to hint the turbo-4 is running on CNG are that it’s a little louder than normal, and it feels like it’s working harder to deliver power. It's far from the forklift feel of older, more primitive CNG conversions, though.
At speed, the g-tron behaves like a standard gasoline or diesel A5 Sportback. It’s on the comfortable side of dynamic, with precise, well-weighted steering and a playful chassis.
The suspension strikes a balance between supple and firm to provide buttoned-down handling without hammering occupants one pothole at a time. The driver can choose among several driving modes, including Dynamic and Comfort.
The CNG-powered model weighs 220 pounds more than the regular A5 Sportback, which certainly doesn’t help performance. Most of the extra pounds are in its rump, so the tradeoff is that the CNG tanks actually improve handling by adding more mass over the rear axle, which evens out the car’s weight distribution.
We noticed it because our drive took place at Bosch’s proving grounds in Boxberg, Germany, and included time on a fast-paced test track. You likely won’t sense the difference if you’re simply driving on short trips around town.
The optional navigation system should be considered a necessity in a car like the A5 g-tron. We'd suggest it should be included as standard to reward motorists who take a leap of faith and live with a CNG-powered car.
Audi has added an extra function to its MMI interface that lets the driver search for the nearest CNG station. Many electric cars offer a similar function to help drivers locate nearby charging stations, which are often not signposted.
While the number of electric-car charging stations grows each year, finding a public CNG station largely depends on where you are.
The navigation system discovered a surprising number of stations within 20 miles of our Boxberg, Germany, test—but in other parts of the world, trying to find a public natural-gas fueling station is a disheartening endeavor.
With only 950 public natural-gas fueling stations in the U.S., it can be viewed as akin to looking for a needle in a haystack, with your hands tied behind your back, while blindfolded.
As a technology demonstrator, the Audi A5 g-tron proves alternatives to traditional fossil fuels can take on many forms.
This one stands out with grin-inducing handling, quick refueling, impressive range, and CO2 emissions as low as those of the smallest, thriftiest subcompact sold in Europe.
But unless the CNG infrastructure improves drastically, Audi's g-tron will remain little more than a stopgap technology niche on the path towards battery- or hydrogen-powered cars with no tailpipe emissions at all.
— Ronan Glon
EDITOR'S NOTE: An earlier version of this story said that the U.S. had only 500 publicly accessible natural-gas fueling stations, but as reader "Carney3" points out, the correct number is 950 per the U.S. Department of Energy. We have updated the story and apologize for the error.