MERCEDES-BENZ shocked the automotive world when it introduced the original A-class in 1998, not only because the company had never previously built such a small car but because it was so different to anything else with its upright styling.

However, while sales have naturally be stronger in Europe, where city cars reign supreme, the A-class has never quite lived up to expectations in Australia, with annual sales consistently running at around the 1000 mark for the last decade.

In fact, the best result remains its first full year on sale here (1312 sales in 1999), yet Benz sales overall in that period have doubled in that period, so the A-class has become less significant for the company since it was launched here.

Mercedes-Benz Australia hopes that might change with the introduction of a diesel engine in the A-class for the first time in the form of the A180 CDI, which arrives along with a mild mid-life facelift for the second-generation W169 series.

Although the cost/benefit ratio of diesel over petrol is generally less of a factor with small cars, Mercedes rightly makes the point that consumers appreciate the extra performance that generally comes from modern turbo-diesel engines with common-rail fuel-injection.

There is also the environmental equation to consider as the A180 CDI produces only 137 grams of carbon dioxide per kilometre compared with 165g/km for the equivalent A170 petrol model.

In terms of performance, the 2.0-litre turbo-diesel engine in the A180 CDI produces slightly less power than the A170’s 1.7-litre petrol (80kW versus 85kW), but does so at lower revs (4200rpm versus 5500rpm).

And when it comes to torque – the big party trick for diesels – the A180 romps home at 250Nm (produced from 1600-2600rpm) versus only 155Nm (at a less useful 3500-4000rpm).

So you would think that the A180 CDI would blitz the A170 on acceleration, but think again – it accelerates from zero to 100km/h only one-tenth of a second faster at 10.8 seconds versus 10.9 according to Mercedes-Benz figures.

The diesel weighs an extra 105kg and obviously that hefty sum is enough to negate the extra pulling power.

On this week’s local media launch, we drove the A180 fitted with the optional CVT (continuously variable transmission) and the first thing we noticed was that very lack of low-down pull, especially with a couple of passengers on board to add to the weight penalty.

Once mobile, however, the diesel comes into its own and we would expect that the mid-range acceleration figures would be much more favourable to the diesel.

With the performance equation put to one side, then, customers will need to value the lower environmental impact and also the improved consumption – and on that score, the A180 wins hands down, with a combined figure of just 5.2L/100km (with the six-speed manual gearbox) versus 6.9L/100km for the A170 (with a five-speed manual).

Even with high prices for diesel at the bowser, that means weekly savings for diesel buyers, but how long will it take to get back the extra $2000 the A180 costs?

And one more factor to throw into the equation – noise. Little cars like the A-class do not have a lot of space and sound-deadening between the occupants and the engine, so you get quite a bit of diesel rattle coming through into the cabin.

For me, that would tip the equation in favour of the A170, which was not available on the launch drive, but which is sure to feel a little more refined. And you are hardly going to feel like an environmental terrorist driving a car with such good economy in the first place.

Most of the facelift changes on the latest A-class are cosmetic, so the drive experience will not have changed much in the last few years.

While the CVT transmission performed very well – in both auto and pre-selected manual mode – we found the electromechanical steering to be heavy and dead, with no on-centre feel.

The suspension was rather bouncy on the country roads we traversed, especially at the rear, and transferred a lot of road noise through to the cabin. Perhaps the A-class would be better in its natural environment around town, where its compliance would be appreciated and the bounciness and road noise might not be as noticeable.

The larger B-class is certainly a better overall driving proposition, but it costs $6300 more for the diesel version and the fuel consumption is 10 per cent higher. Yet more equations...