Merc's incredible IAA concept is the world’s slipperiest car

Mercedes has a real thirst for aerodynamics right now. Lots of Benzes generate the lowest drag in their class. The little CLA saloon is no beauty, but it’s actually the world’s slipperiest production car. Its drag coefficient is a shark-like 0.23Cd.

And yet Merc’s headline act for this year’s Frankfurt motor show, the imaginatively titled ‘Concept IAA’ makes the CLA look about as svelte as a block of flats. Its drag coefficient? Just 0.19Cd.

‘IAA’ in this case doesn’t actually stand for Frankfurt’s official show name (Internationale Automobil-Ausstellung) but for ‘Intelligent Aerodynamic Automobile’.

The show car is a shapeshifting S-Class-sized beast of a four-door coupe, which automatically grows 390mm in length when you pass 50mph. Bonkers.

The front bumper features panels that extend 25mm forward into the airflow, while a Cruella deVil-spec valance protrudes an extra 20mm out of the back. The front bumper retreats some 60mm underneath the car, and even the wheels seal up to cut drag. Think of it like a falcon – or a jet fighter – tucking in its wings when it dives through the air.

Meanwhile the lights and exhaust are hidden inside the bodywork, McLaren P1-style. Nothing is allowed to interfere with the precious aerodynamics.

Why go to such an effort just to cut drag? Well, the cost of reducing a car’s emissions by 1g/km is currently running at about a billion euros, according senior car industry bods. Creating a slippery body that scythes through the air easily is a no-brainer for saving fuel.

So the Concept IAA uses a Prius-like teardrop shape, tapering from a sharp front to an abrupt, decked tail. That profile is simply the most efficient form for a car to take.

Of course, lots of cars now have active grilles and wheelarch shutters to direct airflow more kindly at speed, but nothing out there actually grows like the Concept IAA. With eco-regulations getting ever stricter, this is potentially a logical next step for production. Hope so – it looks excellent.

Obviously this is a proper concept car – you couldn’t put some numberplates on the front and crumbs in the seat cushions and call it the next CLS. But ideas from the IAA making production hopefully isn’t too far-fetched an idea.

Take the cabin. It’s not wild or silly, and obviously related to the current S-Class’s cockpit. A few more touchscreens here, some trendy blue lighting there, but nothing stupidly outlandish.

The powertrain’s the same story. Merc has gone for a petrol-electric hybrid set-up developing a modest 275bhp, yet good for a 155mph top speed. Nothing too scary there.

Officially, the IAA will cough out 31g/km and go 41 miles in on battery power alone in regular ‘Design’ mode. Play the Optimus Prime trump card and those figures improve to 28g/km and 38 miles when in fully extended ‘Aerodynamic’ guise.

Unimpressed? Mercedes is at pains to point out the official tests are skewed towards dog-slow urban driving, where aerodynamics are basically irrelevant.

Still, imagine blatting down the autobahn in a telescopic, extendable slippery eel of a car. It’s a land speed record streamliner for the 21st century. Make one we can all buy, please, Mercedes.