Top Gear’s Top 9: slippery low-drag cars

This week, Mercedes demonstrated yet again that, if you want to make a car cut as clean a hole in the air as possible, you need a smooth, teardrop shape. Ideally with a long tail and as few panel gaps as possible. The new EQXX concept is basically a C-Class-sized four-door saloon, but because it disturbs the air around it so little, it’s good for a claim of over 600 miles of electric range. 

And that got us thinking: what other cars have set out not to generate the most downforce from the air around them, but to cut through it most efficiently? The pursuit of low drag has created some rather strange and special cars…

One of the earliest road cars designed with high-speed aero in mind was the sensational (and infamous) Tatra 87 of Czechoslovakia. Think of it as a cross between a VW Beetle, a muscle car, and a bullet train. Yep, now you’re listening.

Designed to cruise at up to 100mph on the new German autobahns, the Tatra was powered a rear-mounted 2.9-litre V8 with 85bhp (a lot, in the 1930s) but thanks to its low-drag shape it was also extremely economical, good for almost 20 miles per gallon (again, it was a different time).

The car’s profile was inspired by the enormous German airships of the same era – note the fin on the back for high-speed stability. Sadly, it didn’t do the Tatra much good: the arse-engined, primitively suspended 87 was so lethally hard to control in corners that it earned a wartime reputation as ‘the car that killed more high-ranking Nazi officers than enemy action’. It’s alleged that the 87 was so accident prone, high-ranking Nazis were actually banned from travelling in them. 

So, not the most refined design of chassis ever… but the Tatra is a war hero. 

Was there ever a less futuristic-sounding car company than ‘Oldsmobile’? Probably not. But the now defunct brainchild of one Ransom E. Olds did innovate plenty during its century of existence. 

One of its wilder adventures was the Aerotech series of record-breaking concept cars built between 1987 and 1992. Essentially a publicity vehicle to showcase a new type of workaday Oldsmobile 4-cylinder engine, the racecar-like Aerotech featured adjustable underbody aero and was good for speeds of up to 257mph in short-tail trim and over 275mph with a longtail rear fitted, in the hands of four-time Indy 500 winner A.J. Foyt. 

Ah yes fact fans, before the Toyota Prius, there was this: the original Japanese hybrid streamliner. Honda’s first Insight landed in 1999, a two-door hatchback coupe thingy good for a claimed 64mpg, but enthusiastic owners soon learned that over 70 miles per gallon was there for the taking.

With a drag factor of 0.25Cd, the lightweight Insight was the slipperiest car in the world at the time of its revealing, and even today it makes modern hybrids look unradical and lazy.

And from a car designed to save the planet, to one that began life making sure drivers didn’t spend too much longer on the planet. Early 917s were literally lethal: impossibly fragile and prone to going light at speed. Just what you want as you roar down the fearsome Mulsanne straight in the pitch black of the Le Mans 24 Hours, doing a cool 200 miles an hour. 

Porsche worked hard to tame the stability of its prototype endurance racer, and the long-tail ‘Langheck’ or LH trim was tested to a 225mph v-max, while exhibiting more downforce than the earliest 917s mustered. While it wasn’t the most dominant form of the 917, the LH’s twin fins and rolling hills bodywork made it one of the prettiest racing Porsches of all time.

How’s this for a first effort? The 92 was literally Saab’s first ever production car, and instead of playing it nice and safe, the Swedes innovated. Hard. 

They came up with a body that was stamped from a single sheet of metal, easing production costs. There was a device incorporated into the oil system to stop oil starvation when the car was coasting. And despite only offering 25 horsepower from its 764cc two-cylinder engine, the 92 could reach 65 miles an hour, because the body had a drag coefficient of 0.30Cd – some feat for 1949. 

Lots of Saabs riffed off aeronautical connections in the decades that followed, but the grandaddy of them all was a true aero pioneer.

From a 25bhp veteran to a 250mph wedge of unobtanium. The 1055bhp Speedtail is McLaren’s fastest ever car – beating the legendary F1 by a few scant mphs at the top end – but it gets there so much faster because it’s got the full works: hybrid boost, turbocharged oomph, modern tyres, a twin-clutch gearbox, launch control… and the profile of a shark. Not a lumpy hammerhead or a big ol’ great white: this is a pointy tigershark of a car.

McLaren because so obsessed by cutting drag that instead of a rear wing, actuators literally bend the rear bodywork to create downforce, while the cameras (of course door mirrors were banned) retract at speed to shave off even more resistance. Not likely to be overtaken, is it?

What with The Whole Dieselgate Thing, the reputation of VW’s 21st Century streamlined pebble has probably been damaged beyond repair. The XL1 still looks so fresh, you’d imagine someone at Volkswagen is tempted to rip out the 800cc two-cylinder hybrid diesel engine, shove a few batteries in, call it the ‘ID1’ and head down das beerhall. 

Launched as a limited production model in 2012 after a decade of toying with 100km-per-litre concept cars, the butterfly door’d XL1 seated two passengers in a semi-tandem formation in its carbon bodied shell. 

Faired-in rear wheels, a tiny frontal area and cameras replacing door mirrors add up to a barely believable drag coefficient of just 0.186Cd, which is less than a paper aeroplane. 

Only 250 were made, costing £120,000 a piece, while servicing costs are so eye-watering you’d be better off running a V12-powered Aston Martin and burning tenners to keep warm. But as VW Group technical follies go, it’s cheaper than a Bugatti.  

We’ve come back to Mercedes to round out this collection of streamliners because you might have forgotten one of the weirder attempts of recent years to make a car slippery. This is the Concept IAA, or Intelligent Aero Automobile.

It has motorised shutters to close off the grille. More motorised shutters to smooth off the wheels. And this is all very clever. But no-one ever talks about that.

No, we remember the IAA for its Extendable Bum. 

That’s right, this CLS-style coupe-saloon had a party-piece posterior. At 50mm, its bottom grew by 390mm, smoothing airflow off the rear and easing drag down to 0.19Cd – a world record for a four-door car. 

Probably not much good for rear crash impact regulations. Or boot space. The new EQXX doesn’t have a telescopic rump, which probably means it wasn’t strictly necessary. 

Pity. We’ll always remember the IAA for that, though. Secretly, it should’ve stood for ‘Inch-Adding Arse.’