WE WERE RUNNING AGAINST THE WIND [509]

The Mercedes-Benz A-Class saloon

For someone that cannot drive, I talk about cars a lot, mostly about how they were designed, like the Citroën CX, or because they provoked a silly culture war, like Ford replacing the Cortina with the Sierra.

Both as an observer and passenger, little is left to do wrongly in building a car, decades of lessons having been learnt. This was what I thought upon seeing a Mercedes-Benz A-Class saloon, which purported to be a “sub-compact” version of their larger cars, while competing on size and price with the Volkswagen Golf, Audi A3 and Vauxhall Astra. All these cars have similar sweeping lines, rounded edges and recessed door handles, numerous attempts at achieving the most aerodynamic shape of vehicle producing an “average” shape.

And yet, the choices Mercedes-Benz made – the low, aggressive front nose, the rounded boot, and shutters that control air flow through the grille – meant they claimed, when it was introduced in 2018, that it had the lowest-drag co-efficiency of any production car. The hatchback version achieved a figure of 0.25, while the saloon achieved 0.22, which is better than a Tesla Model 3 or BMW 3-Series, while matching that of the Porsche Taycan.

If this had been the 1980s, the number “0.22” would have been written somewhere on the car, just as the 1982 Audi 100 had “Cd 0.30” emblazoned on its sides, such was the monumental achievement. That the A-Class has now been axed, without any further fanfare, by Mercedes-Benz, now preferring to focus on larger cars, without any further fanfare, speaks to how easy producing an aerodynamic shape is expected to be.

Drag co-efficiency, measuring the resistance on an object as it is moved through air, water or other “fluid” environment, was once a major selling point for a car. Put extremely simply, a drag co-efficiency score comes from measuring drag – the force opposing an object as it moves through an environment – versus the mass, speed and surface area of the object.

Car companies want to reduce the drag on their cars because it makes their cars faster and more efficient without needing to produce more power, while speaking to build quality through removing any areas where air can be trapped, by both smoothing out body panels and reducing or eliminating the gaps between them. The TV ad for the Audi 100 dramatised this as letting go of parachutes that were holding the car back. 

However, regardless of how the drag-co-efficiency score is produced, the fact that that the lower to zero the score is, the more aerodynamic the object must be, is enough to make use for marketing purposes. For example, the “jelly-mould” styling of the Ford Sierra was a major departure from the boxy styling of the Ford Cortina it replaced, taking some time to grow on British car buyers, but in reducing drag co-efficiency from 0.45 to 0.34, reducing fuel consumption from the engines that were carried over from the Cortina.

Computer-aided design advanced both the drafting and refining of a car’s aerodynamics over the testing of clay models and one-off prototypes. Citroën famously achieved low drag on a number of cars, including the SM coupé, and CX and GS saloons all achieving a figure of under 0.35 during the 1970s, but the British Leyland Princess range, later becoming the maligned Austin Ambassador, only managed around 0.40, typical for a 1970s car designed on paper, but also of poor fit and finish. The Austin Allegro has also been panned as a car more aerodynamic when driven backwards, but I could find no figures to claim either way.

Now that an “average” car shape has been reached – a child drawing a car would now draw an egg with wheels than a three-boxed shape – drag co-efficiency means little. The Ford Puma SUV, the biggest-selling car in the UK, achieves a figure of 0.31-0.32, like its competitor, the Vauxhall Mokka – I guess it is something about being that bit taller off the ground than a regular car. The Audi A3 couldn’t beat the A-Class with 0.28-0.29, but it is at least still in production. Even the latest Cadillac Escalade, essentially a large building moving at speed, has a figure of 0.36. Tesla, BMW and Mercedes-Benz can reach towards 0.2, but only with their saloon cars.

I had to look – the card game “Top Trumps” did not use drag co-efficiency in their car-themed sets, as doing so may require renaming the game.