Audi Q7 v Mercedes-Benz ML320 v BMW X5 2007 Comparison

Q7 v ML v X5

Listen hard and you'll hear it: a cloistered clatter, a refined rattle, emanating from our more expensive suburbs, ski resorts and elite beach-side peninsulas.

It's the increasing popularity of turbo-diesel engines, usually driving all four wheels of a German high-rise wagon. Like these three - the newly arrived BMW X5, the almost as fresh Audi Q7 and Mercedes-Benz's older (but not aged) ML.

As surprising as it may sound, in the fashion-conscious world of luxury SUVs, compression-ignition engines nowadays account for nearly 50 percent of all sales.

BMW forecasts as much as 70 percent of E70 X5 sales will be diesel, continuing the trend set by its top-selling and much-respected E53 predecessor. So lining up the X5 3.0d against its logical opponents - the ML320 CDI and the Q7 TDI - is not some niche, goofy dalliance. This is a heavyweight bout; the luxury SUV equivalent of Commodore, Falcon, 380 and Aurion petrol sixes going at it.

And there's also a sub-text. The original X5 was widely regarded as the best-driving SUV going around. Has its successor maintained, surpassed or even slipped from those lofty standards?

It certainly hasn't broken the mould in transition. Like its predecessor and its rivals, the E70 is based around a unitary construction and a light-duty all-wheel-drive system. And like them, it was created to cater primarily for North American tastes. It's even built there, along with the ML.

But the turbo-diesel drivetrains this trio employ are the result of a European predilection fostered by favourable tax regimes. All employ aluminium crankcases, double overhead camshafts, four valves per cylinder, common-rail piezo direct injection, variable geometry turbocharging, intercooling, and meet Euro IV emissions.

Given all that, the parity of their outputs is hardly surprising. The BMW knocks out 160kW and 500Nm, the Audi 171kW and 500Nm, the Benz 165kW and 510Nm. In all three cases, that truck-load of peak torque arrives well below 2000rpm and flat-lines almost all the way to 3000rpm.

These three are a far cry from the noisy, slow, cast-iron warhorses of old, although - despite the sales figures - still not clearly a better choice than their petrol equivalents.

Yes, the turbo-diesels are more fuel efficient, but there's a price premium to pay. Yes, they produce far superior torque, but they offer nowhere near the power and revvy flexibility that an enthusiast driver enjoys in a petrol engine. And while their carbon count is lower, their people-poisoning particulate emissions are higher. The obvious conclusion is the buyers of these wagons are adopting this technology not only because it works, but because it's fashionable ... and relatively affordable.

That affordability is aided significantly by the five percent SUV tariff that helps them heavily undercut the more heavily taxed low-riding luxury offerings. For instance, a 530d sedan is $115,000, a 530i Touring $119,500.

It's the Q7 which is the 'bargain' at $85,700. The ML in Luxury spec is $90,900, while the X5 Executive (a new designation introduced with E70) comes in at $96,300.

The Q7 looks even better when, on top of the long list of standard safety and luxury gear, you factor in sat-nav, a reversing camera and the only standard full-size spare tyre on offer. But having to adjust the leather front seats manually is laughable at this money.

The ML Luxury is the default CDI choice nowadays. It misses out on sat-nav and, significantly, a reversing camera.

The BMW in Executive spec is almost the complete package, but lacks bi-xenon headlights. And metallic paint is a $1700 option too. If you think that's a gouge, Audi charges $2000 and Mercedes-Benz $2500.

Options is a place where money is to be made, as the extra equipment added to all three test vehicles emphasises. Indeed, their pricing ended up within a few hundred dollars of each other on the north side of $101,000.

The list included the Audi's $6750 (!) panorama roof, $2900 tow-hitch pack and $1700 Bluetooth preparation. The Benz added a $4000 Comfort Package including sunroof, folding mirrors and luggage retaining net, and the $4500 Exterior Sports Package, which included bi-xenon headlights and 19-inch wheels shod with low-profile Pirelli P Zero Rosso rubber. A $3500 panorama sunroof was the BMW's most expensive option.

One key option the test BMW didn't come with was the $5000 third-row kiddy seat, something made possible by the 100mm growth in wheelbase and 187mm stretch in overall length. Overall width is also up, along with height and track widths. Weight, however, has been held at 2105kg.

There's no chance of the X5 matching the Q7 for size or heft. Audi has made up for a tardy arrival in a booming segment by claiming as much real estate as possible, and making the look equally as imposing.

Chrome bearded, eagle-eyed and 5086mm long, it stretches way past both the X5 and ML. The Q7 is also 50mm wider than the X5 and has an over-3000mm wheelbase. It weighs in just five kilos under 2300kg.

The second-generation ML, on sale in Oz since September 2005, is dimensionally the smallest vehicle here and arguably the best looking. It splits the two X5 generations in measurements and is well shy of Q7 on wheelbase, length, width and tracks. It is the tallest, however, and weighs in 5kg heavier than the X5. It's also the only vehicle here not to offer an optional third-row seat; Merc leaves that to the GL-Class.

Now, if you're looking at this X5, twisting the page around and squinting a bit, don't worry, it is brand new. It's one of those classic BMW cases of every panel being different but the end result superficially the same.

But forget all that and clamber into the driver's seat. From this perspective, it's the BMW which promises the most. Deep, almost pliant by German standards and heavily bolstered, there is real support. The steering wheel has the smallest rim width and its diameter is just about right. Details like these make you feel in the zone, suggesting there's been attention paid to the driving as well as the packaging.

And so it proves over Melbourne's Black Spur. This is the gateway to Victoria's snow and lakes playground; twisting, rising and falling violently enough to upset anything with a penchant for lurching weight transfers and understeer. Limited passing opportunities place a premium on engine and transmission response, too.

The X5 is the only one here you'd be even remotely tempted to U-turn and do the run again just for the hell of it. The BMW feels strong and solid, well tuned and integrated. Now more rigid, and equipped with double A-arms front suspension and a forward mounted steering rack, it remains online at high speed in tight corners, resists excessive pitch under heavy braking and steers with a light accuracy that belies its weight.

The X5's impressive rear-biased xDrive all-wheel-drive system also contributes to this controlled and confident behaviour, along with well modulated and consistently strong braking response. It's also the only one of these three where the stability control can be totally - as well as partially - disengaged, and the only one that you'd feel comfortable doing so.

On gravel roads and forestry tracks, the X5 loves to gallop along, is highly adjustable and up for a bit of oppy-lock play. In contrast, the Q7 and ML are shut down by their electronics before things get too sideways.

Despite employing run-flat tyres, the X5's ride is also the pick at lower speeds. As speeds rise, though, it becomes more intrusive than the Q7, perhaps reflecting the stiffer tyre sidewalls and BMW's determination to deliver good handling, despite the higher SUV roll centre.

Not only has the X5's dynamic prowess been retained in a larger package, it seems to have been improved. But let's not get too carried away. The X5 is not - repeat not - in the class of BMW's 5 Series sedans in this sporting domain. More weight and a higher centre of gravity see to that. It's not as emotionally involving; rather, it's a very good effort at banging a square peg into a round hole.

No doubt the turbo-diesel contributes to this slight anaesthesia. Yes, it shoves off the bottom lag-free, providing remarkable launch and overtaking prowess. Yes, it spins harder and freer than the other two. And yes, it feels the most petrol-like and sporting of the three. But it still calls it quits by 4500rpm. When you know there's another 3.0-litre inline six in the BMW lineup that revs eagerly beyond 6000rpm accompanied by snarling aurals, the slight sense of anti-climax is unavoidable.

For many customers, this mass of lag-less bottom- and mid-range response in exchange for lack of top-end excitement is just what's needed for the endless commute. The good news is these characteristics are also available in abundance in the Q7 and ML. The bad news is that they just don't involve and please the driver with the cohesion of the X5.

Despite the X5's run-flats, it's actually the ML which has the most significant tyre issue. The grip level is improved and bodyroll more contained than when rolling on standard 17s, but the ride is unsettled and steering afflicted by variable weighting and pronounced kickback as the limit approaches. Some of this must be attributed to the 19-inch low-profile rubber, as the refinement and ride of an ML is traditionally one of its strongest  attributes.

The Q7 is a surprise simply for its ability to competently and sometimes impressively marshal its substantial bulk. Granted, the steering is at the other extreme to the ML by being uncommunicative and disconnected. But the ride at speed on typically corrugated Aussie roads is the best of the three. This is the choice for that four-up-with-luggage long-haul trip.

The engine plays a key role in this. Despite the Q7's weight, it stays quiet inside or outside the cabin when pressed, and gives ground only marginally to the BMW initially but is soon into its stride and on par. It's particularly strong in mid-range response, edging out both the BMW and Mercedes in the measured 80-120km/h test and then galloping away.

But head into town and the Audi simply feels too big in most circumstances. Judging the ins and outs of shopping centre carparks and the like is a chore. The BMW and Benz are better for this stuff, even if the X5 has a lamentable 12.8m turning circle.

While the ML is the noisiest idler and trails slightly when accelerating, its seven-speed 7G-Tronic transmission adds not only individuality, but slightly smoother shifting, too. There's hardly ever a need to resort to the manual shift buttons on the steering wheel, such is its smooth intuition and sustained momentum.

The Q7 and the X5 both employ ZF's excellent 6HP26 six-speed auto, and nearly match the Benz for both smarts and surreptitious shifting. But in the BMW it's controlled via a new electronic shifter that looks like a broken stick and shifts with a plasticky lack of feel.

For many, though, the bottom line is literally going to be the bottom line. And that means fuel economy. Impressive it is, too. Over the duration of a test that included all forms of bitumen driving and some light-duty work on forestry roads, the BMW led the way at 11.1L/100km, from the Benz on 11.4 and the Audi at 11.6. It's appropriate, given their parity in so many other departments, that even fuel consumption should be a line-ball result.

But we're interested in how they drive as much as how they open, shut, fold, stack and compute. The fact is the BMW is clearly the best at that. Actually, continues to be the best, as generation two successfully defends the mantle of the original. The Q7 is simply too big and ponderous, the ML compromised by unsuitable tyres and a slightly less convincing value equation.

But understand that there are more thrilling, more involving BMWs (and Audis and Benzes, for that matter) than the X5 3.0d. It might be the darling of the elite - clever, sensible, fashionable and even affordable - but personally, for the money, I'd rather drive a 525i.

POWER GROUNDED:

Location: Tooradin Airfield, dry. Temp: 10°C. Driver: Maurie Platt
* Estimated or Manufacturer's claim

Images: Cristian Brunelli