Subtle changes on 1.2 TDI even include aerodynamic wheel trim

The idea that a car can punch through the 100mpg/35.5kpl and 100mph/160kph barriers may seem outlandish but Audi has managed it with the Audi 1.2 TDI.
Not only is this remarkable little car capable of returning 95.4mpg/33.9kpl in the official combined fuel tests (and over 100mpg/35.5kpl at a gentle cruise) but it will also run on to a maximum speed of 166kph.

Cars able to do 35.5kpl have existed inside mathematicians’ notebooks for years and the British company Ricardo has calculated a number of scenarios for such a frugal machine. One specification describes a four-seater with a kerb weight of 700kg or less, a maximum frontal area of 1.8m2, a drag coefficient of 0.25 or less, a 1.0-litre direct injection petrol engine and, for efficiency, an automatically shifted manual transmission (AMT).

The A2 TDI actually falls well short of a number of those criteria. This isn’t surprising, says Audi, because it is designed to compete with the Mercedes A-class rather than its smaller VW Group brethren, the Seat Arosa and VW Lupo, even though it uses a Lupo engine.

Profiles-18%, Panels-60%, Cast Elements-22%

Hi-Tech spaceframe contributes to A2's light weight and fuel economy

The Audi weighs 855kg, has a frontal area of 2.18m2 and is powered by a 1.2-litre three-cylinder direct injection diesel. But it does have a Cd value of 0.25 and an AMT gearbox which can be used in manual Tiptronic, automatic or automatic Eco mode, which optimises shifts for economy. Eco mode also permits freewheeling downhill or when coasting by declutching, as well as the ability to switch itself off when you are at a standstill. T he weight-saving process was trickier still since the aluminium-bodied A2 is already unusually light for its size. That didn’t stop the engineers shaving another 135kg off the 35.5kpl car. The suspension’s subframes, control arms and spring struts are now all made of aluminium - saving 80kg - as are the brake calipers and the rear brake drums. Even the rear seat has been lightened by 19kg. But the final touch is the low rolling-resistance tyres tailored for the 1.2 TDI by Bridgestone and Dunlop. They include Aramid fibres in their sidewalls, helping reduce the weight to 4.9kg per tyre.

To prove the effect of its work, Audi fitted fuel metering equipment to all the test cars. I achieved 39.4kpl over the 24km course while the day’s best was 43.6kpl.

If this is what’s possible from a relatively conventional diesel engine, imagine what an electric-diesel hybrid could deliver. The 150mpg/53.3kpl car can’t be far away.