How aerodynamics have moved cars forward in the past 25 years

I’ve bought an Audi A2. It’s a 2003 74bhp 1.4-litre diesel and, because it didn’t have an MOT, it cost me £500.

So far, I’ve fitted a new rear wheel bearing (£30), cleaned some mould from its crannies and sent it to be MOT tested. It failed only on headlight alignment and parking brake effectiveness, the latter perhaps because it has recently spent time sitting.

By the time you read this, I hope to have sorted both, plus the sole advisory note about headlight cloudiness, meaning I will have a fully roadworthy, clean-MOTed A2 that the tester called “really tidy” for less than £550.

You will hear more about it, of course, in future, and no doubt I will bang on about it at length on the podcast (get it every Wednesday from etc and so on).

But it’s a photo from the previous owner, showing a return of 75mpg, that has got me thinking about just how efficient the A2 is – and could be.

It’s aluminium-structured and compact so has a kerb weight of only 960kg in this form. But while running a sponge over it, I reminded myself how the field of aerodynamics has moved on in the past quarter century.

The A2 TDI had a drag coefficient of 0.28, which a special low-drag, big-economy edition managed to improve to 0.25. It took things like 145-section tyres and an underbody redesign to do that.

Yet today, in cars that somehow don’t look anything like so slippery, figures in the low 0.20s are increasingly common.

On the face of it, the A2 looks a pretty efficient shape. The front is well rounded and the roof arches in a teardrop profile, which is the most aerodynamic shape there is.

Cars could all be incredibly efficient if they were 12 metres long and tapered for a teardrop profile that would retain laminar air flow right along the body.

But they’re not, so air has to break clear of the body somehow, and to cleave it off quickly is better than prolonging its departure, which is why so many modern cars have boot-lip or rooftop spoilers.

A rounded rear end promotes air swirling and creating little eddies, almost clinging to the body and adding drag. That car designers go to the trouble of aerodynamically sculpting rear light clusters shows how it’s worth making even small improvements here.

Especially with EVs, in which aerodynamics play a bigger part in the overall efficiency than in ICE cars, and because more drag doesn’t just add fuel cost but charging time too.

It’s such little details that the old A2 doesn’t have. Its door handles stick out, its windscreen wiper sits above the windscreen edge and there’s (very subtle) body cladding.

Practicality and regulations played their part too. The A2 has a little lip spoiler on its hatch, which could be more efficient if it were bigger, and could extend vertically down the sides of the car too, like the ones they put on the back of lorries.

But that would make rear visibility even worse than it is and could have spoilt the lines of what I think is a very pretty little car. Ditto if the rear lights had been sculpted, rather than shaped to match the body: more efficient, less attractive.

There are things Audi didn’t do at the time, then, that it would feel almost compelled to do today, especially on a car marketed, as the A2 was, as technically clever and uber-efficient.

Still, for a late-1990s design, it’s hardly shabby. I haven’t done the calculations, but there are estimates that it would take only 10bhp, plus or minus (probably plus) a couple, to propel an A2 on the flat at 60mph.

Which sounds like not a lot until you remember that a hire go-kart, much lighter and smaller but much less slippery, will do about the same with similar power.

I think making an A2 as slippery as possible would be a fun project: reshaping its spoilers, fairing-in its rear wheels, extending its bonnet and so on.

Yes, I know that none of those things would make it as efficient as an EV. And save for fitting skinnier tyres, I’m not going to do any of them anyway. I’m just going to enjoy this little marvel for what it is.