Maker proves it's Holden the line

Despite queuing for the ferry, the Omega aced its fuel challenge. Photo / Leon Kirkbeck

How thirsty is your car? That answer will depend on who is driving it, what the weather and traffic conditions are, and even what pressure you've pumped your tyres to.

That's why car company figures can seem misleading - and why Holden has just run an Auckland to Christchurch fuel challenge.

Five cars. A mandated average of 80km/h over a fixed route. Ignition and air-con on, and no drafting - it's dangerous. If we slowed to improve fuel economy and failed to hit our target speed, we'd be penalised.

We drove a 3.0-litre V6 Omega sedan, alongside a 3.6-litre V6 sedan, a 3.6 wagon - and a top-spec Calais piloted by Shane Hart, who'd won his drive via a Facebook contest.

Auckland to Taupo - easy, given it's mostly open road and you can use cruise control. My co-driver set it to 90 and pointed her south for a trouble-free run to lunch, and a 7.7l/100km average.

I took the tiller for the tricky run past the lake, then the climb over the desert road and on to Bulls. I knew the road, and could better anticipate - to minimise brake use and maximise momentum.

But cruise control wasn't an option, and though the auto can be driven as a manual, you must transit through "sport" first, which may result in unwanted revving. Yes, we were taking it seriously by now, and hit 7.5l/100km, despite the demanding terrain and maddeningly relaxed traffic.

The run to Wellington was a cinch, my co-driver hitting just two red lights and with rush hour long over; this was the most frugal leg for all but one car.

Queuing for the ferry scuppered our average next morning. Still, the Omega was cosseting our bums, the iPod hadn't run out of tunes and the best of the scenery was still to come.

The trickiest too, with the long climb out of Picton, then into the teeth of a howling southerly, battering the car's nose and killing our economy efforts. The last stretch at 98km/h, then an unseemly tangle with Christchurch's one-way system and some navigational hiccups. Still, we were first into the Holden dealer, still on the original tank. We'd averaged 79.57km/h, and 7.6l/100km. That's well under Holden's 9.3l/100km claim, and impressive for a car of this size.

Shane ran out just 17km short, having indulged in a bit of throttle play en route, then driven over-conservatively to make up - his 75.87km/h average well under our target. The 3.6 wagon came in at 8.1, at 78.56km/h.

Could you achieve the same in your Commodore? On this trip, yes. At home? Perhaps not. You might have a roof rack, or a lead foot. That's why car companies publish fuel figures obtained in a laboratory under fixed rules. They don't replicate your world, but let you directly compare your model to another tested under identical conditions.

Most companies publish a "combined" figure, which incorporates a strict city-urban ratio.

Still, that a Holden Commodore could drive from Auckland to Christchurch on a tank proves the value of fuel injection - and that what you do behind the wheel can radically affect your tally at the pump.