AUDI’S niche-within-a-niche A5 range rollout continues with the Australian debut of the five-door supercharged V6 S5 Sportback.

Slicing the prestige market thinner than gold leaf as it heads towards a whopping 42-model range globally by 2015, Audi predicts this 245kW quattro sports flagship of the Sportback hatch range will account for 10 sales a month, which equates to a third of S5 volume or just one per cent of Audi's predicted total 1000 units a month for the rest of 2010.

Aimed at buyers who want five-door practicality with the sharpness wrought by Audi’s ‘S for sport’ treatment, the S5 Sportback is the third model in the A5 range to cop this makeover, the others being the two-door S5 Coupe and S5 Cabrio.

It is also the third A5 Sportback variation to hit the market since the mid-sized luxury hatch was launched in 155kW 2.0-litre TFSI four-cylinder and 176kW 3.0-litre TDI diesel V6 models in January.

The last stanza in the 2010 A5 range songbook will be played in October when the no-holds-barred, range-topping V8 RS5 Coupe arrives to relegate the S5 variants to good-but-not-best status and to take the fight up to the benchmark BMW M3.

Unlike the RS5, the S5 Sportback has no natural rivals, straddling the five-door family prestige segment and the hard-edged sports market usually inhabited by European two-door coupes or four-door sports sedans.

Like the S5 Cabrio and the related S4 sedan, the S5 Sportback eschews the naturally aspirated and aurally magnificent 260kW/440Nm 4.2-litre V8 power that blesses the S5 Coupe, in favour of the 245kW/440Nm supercharged, direct-injected TFSI V6 that made its debut in the current A6 range.

AudiA5 center imageIn Audi-land, ‘T’ stands for supercharger, but we have already opened that can of worms in previous articles, so we will leave that alone.

Never one to waste a good engine, Audi parent Volkswagen Group has even purloined this TSFI 90-degree V6 to provide the petrol power for hybrid variants of its VW Touareg and Porsche Cayenne.

The first Audi engine to use supercharging since its Auto Union ancestor was blitzkrieging European race tracks – Audi has long been a proponent of turbos – the longitudinally-mounted V6 is puffed up by a blower nestled in the V between the cylinder banks, providing 0.8 bar of extra and instantaneous urge.

In S5 Sportback guise, the engine pumps out the same 245kW as it does in the S4 and S5 Cabrio, as well as identical 440Nm torque between 2900rpm and 5300rpm.

That torque peak, incidentally, is the same figure produced by the 4.2-litre V8 in the S5 Coupe, but thanks to the force-fed nature of the V6, maximum grunt is achieved at lower revs than the naturally aspirated V8’s 3500rpm peak.

With a little less weight and a little more power (260kW), the three-door V8 Coupe retains the S5 straight-line performance crown, zipping from zero to 100km/h in 5.1 seconds, compared with the bulkier five-door Sportback’s 5.4 seconds.

At the petrol pump, however, the S5 Sportback rewards the driver with 9.4 litres per 100km combined fuel economy (and 219 grams per kilometer CO2 emissions), compared with the hairy-chested V8 sibling’s 10.8L/100km.

That fuel economy is aided by Audi’s electricity recuperation system that gives the battery an extra zap during deceleration and relieves the load during acceleration.

While the S5 Coupe is offered with a choice of six-speed dual-clutch auto and manual transmissions, the S5 Sportback keeps the choice easy by dispensing with the manual cog-swapper to offer only the so-called S Tronic dual-clutch auto with the paddle shifters, but going one better with seven speeds.

Like all Audi sports models, the S5 Sportback shares the power around all four wheels via Audi’s Torsen quattro permanent all-wheel-drive system, which, Audi confesses, shows a increased bias to the rear wheels.

It can, under sufferance, put 65 per cent of the drive to the front wheels, or up to 85 per cent to the rears.

A ‘sports differential’ is part of a dynamic handling package at an extra $6900. This device distributes the drive between the rear wheels according to grip. In cornering, most of the torque is sent to the outside wheel to push the car around the corner for more neutral handling. Reaction time, Audi says, is 100 milliseconds.

That optional package also includes Volkswagen Group’s adaptive suspension system with three settings for normal, sporty and comfort ride and handling.

The S5 Sportback clings to the road through 18-inch alloy wheels shod with 245/40 tyres (19- and 20-inchers are a $2900 option).

With extra side doors to accommodate compared with its two-door bretheren, the S5 Sportback is 60mm longer in the wheelbase and 38mm longer overall than its two-door S5 Coupe and Cabrio stablemates.

But just because it has a roomier cabin with easier rear-seat access, it does not get more seats, accommodating only four occupants like the Coupe and Cabrio. While a small person could perch in the middle of the rear bench, no seat belt is fitted. No five-seater is planned, Audi says.

Luggage space is more commodious and flexible than either the S5 Coupe or the cramped Cabrio, with 480 litres of boot space in which to spread your belongings with the rear seats up, and 980 litres with the split rear seats folded.

Using Audi’s tried and true five-link front suspension and trapezoidal rear set-up, the S5 gets the extra sharpness of Audi’s ‘S’ sports tune for superior handling befitting its extra horsepower.

S5 Sportbacks are differentiated externally by subtle enhancements, including more pronounced chrome vertical bars on the grille, a rear lip spoiler, aluminium-covered exterior mirrors, aluminium blades on the front splitter and rea diffuser and quad exhausts pipes in place of the dual numbers on the other Sportbacks.

Electrically adjustable sports seats clad in black leather with alcantara inserts are standard, along with three-zone climate control, keyless entry and start, parking system, Bluetooth, iPod connectivity, sat-nav and obligatory LED running lights are standard.

At $129,300, the S5 Sportback is a $31,000 premium over the next most expensive A5 Sportback, the 3.0-litre TDI, and $50,900 more expensive than the entry-level model powered by the 2.0-litre TSFI four-cylinder engine.

The S5 Sportback is nevertheless the cheapest S5 variant, slipping under the S5 Coupe ($133,500) and crop-top S5 Cabrio ($138,100).