CARS have been getting steadily larger over the last decade and, with the increases in weight and dimensions, engines might have been expected to get bigger, too.

This has not been the case, however. More advanced engine designs have allowed car builders to get more power from familiar capacities without sacrificing reliability. Rather than increasing in size and power, they have merely increased output.

And now the things are going even further. While cars continue to grow in stature, the engines powering them are shrinking in size.

Take Audi’s A3 Cabriolet. Leaving aside the folding roof for one moment, the A3 is a vehicle that competes alongside the Volkswagen Golf, Vauxhall Astra and Ford Focus – albeit aimed at a more premium market. Take examples of these cars from 15 years ago (in the case of the Focus you’ll need to exchange it for its predecessor, the Escort) and the A3, like its contemporaries, dwarfs them.

Despite this, Audi’s A3 Cabriolet can now be equipped with what seems like an outrageously small capacity 1.2-litre engine. That’s even more remarkable where the cabriolet version is concerned as, despite the canvas roof, the model suffers from the same weight issues as nearly all convertibles thanks to the extra motors and chassis-stiffening required, and weighs in at nearly 100kg more than its three-door equivalent.

Audi, along with its Volkswagen Group stable-mates has ‘previous’ when it comes to setting trends with small capacity engines. Previously, it was the 1.4-litre unit, available in turbocharged and twin-charged (supercharged and turbocharged) form, which raised eyebrows with its capacity-belying performance.

The 1.2 TFSI unit also uses forced induction to boost performance to respectable levels while keeping fuel consumption and emissions low. A replacement for the 1.6-litre unit, it lowers CO2 emissions by 35g/km and raises fuel economy by 9.2mpg while improving zero to 62mph acceleration and top speed.

It’s a highly charismatic unit that adds a lot to the A3 Cabriolet package. Both compact and sophisticated in their own rights, car and engine seem made for each other.

Much of the charisma comes in the form of the engine note; a distinctive grumble that’s everpresent but rarely intrusive. With the roof down it adds to the driving appeal, offering a sports inspired – if not sporty – soundtrack.

If it’s outright performance that’s sought, perhaps the 1.2 TFSI is not the best choice, but considering the impressive real-world economy and tax-lowering emissions it does a good job of shifting the A3 Cabriolet. Despite the turbocharger dependency, power does not arrive in lumps of high boost, instead being evenly spread across the revrange.

The chassis is impressively rigid, too, with scuttle-shake contained roof up or down and little flimsiness apparent at the wheel even when ‘pushing on’.

To really gather pace, the 1.2 TFSI A3 Cabriolet needs to be worked fairly hard, but a standard six-speed manual transmission means there’s enough choice to ensure that the correct ratio can always be found. A longer sixth helps with motorway cruising, too. The little engine is comfortable at motorway speeds with largely impressive refinement, although a little wind noise can reach the interior.

The A3 Cabriolet really shines away from the motorway. The smallest capacity engine is at home in a town environment with its impressive urban fuel consumption figures and slick, easy-to-drive nature. With the roof down on a country road or a beach-side boulevard, it looks and feels chic, smart and sophisticated.

Where Audi has succeeded with its smaller cars, including the A3, is the grown-up feeling inside that’s reminiscent of the larger executive models. Despite the more care-free, frivolous nature of a convertible, the A3 Cabriolet has this premium feel and maturity in spades.

In Sport trim the model has an executive appeal. Varying colour options for the quick-folding, onetouch electric roof add to the upmarket feel as do impressive materials and impeccable fit and finish inside.

Compromises come in the form of a small boot opening, restricted rear seating and a slightly firmer ride on the larger alloy wheels, but as a complete package the model offers a level of style and quality that’s rare in the sector. Add increased economy and the A3 Cabriolet’s appeal gets bigger and bigger while the engines get smaller and smaller.

fact file

Audi A3 Cabriolet 1.2 TFSI Sport

PRICE: from £21,180

ENGINE: 1.2-litre petrol unit developing 103bhp and 129lb/ft of torque

TRANSMISSION: six-speed manual transmission, driving the front wheels

PERFORMANCE: maximum speed 118mph, 0-62mph 12.2 seconds

ECONOMY: 49.6mpg

CO2 RATING: 132g/km