SPY PICS: BMW 8 Series Convertible closer

Little more than a week after the debut of the BMW 8 Series Coupe, we have caught the Bavarian brand’s engineers out testing the 8 Series Convertible.

Its rough shape was seen in patent filings uncovered last week but we spotted a prototype on the autobahn outside Friesing, near Munich, with its engineer enjoying some summer sunshine while testing the big four-seat drop-top.

The big-daddy 8 Series Coupe has already begun production at Dingolfing in Germany, and made its dynamic debut at the Goodwood Festival of Speed last week, with European deliveries scheduled for November this year.

But the BMW 8 Series Convertible has been harder to spot. Along with the 8 Series Gran Coupe four-door, the Convertible has been notably absent from BMW’s public statements.

The Gran Coupe, closely related to the BMW Concept M8 Gran Coupe that stunned this year’s Geneva motor show, is slated for production late next year.

The two-door convertible may even beat the four-door coupe to production, but not by much.

While visibly identical to the 8 Series Coupe front the front end to the A-pillar, our pictures show BMW’s new flagship convertible is unique from there to the back-end. Where the Coupe is all long and sleek, the Convertible moves to a flatter tail.

It has its own A-pillars, strengthened internally rather than externally to preserve the windscreen angle of the Coupe, and sources suggest it has thicker windscreen glass, too.

The bootlid is flatter, without the need to accommodate a sloping rear glasshouse, though it finishes off with the same overbite flourish as the hard-top.

It retains the windblocker system its predecessor also used, eschewing such wind-diversion devices as Mercedes-Benz’s Air Cap to divert airflow up and over the cabin. This inevitably means the rear-seat occupants will find it fairly windy at speed.

There will also be a different silhouette from the Coupe, with the folding cloth roof sliding back into a permanent slot beneath the bootlid and fixing in the up position with cloth buttresses joining the rear quarter panels on either side.

The car we stumbled upon had two fat exhaust outlets, indicating it was running the M850i xDrive powertrain, with 390kW of power and 750Nm of torque from its new 4.4-litre twin-turbo V8.

It’s claimed to hurl the 8 Series hard-top to 100km/h in 3.7 seconds, so the Convertible should reach the same mark in less than 4.3 seconds.

The diesel powertrain option of the new Coupe, the 840d, should also sneak inside the Cabriolet, with 680Nm of torque from the inline six-cylinder motor, and fuel consumption should rise marginally from the claimed 6.2L/100km in the lighter hard-top form.

Both variants use eight-speed automatic transmissions hooked up to a variable all-wheel drive system that can switch quickly from a pure rear-drive stance into a grippier torque spread as needed.

Unlike the 6 Series Convertible it replaces, the 8 Series Convertible will sit on its own stand-alone platform, rather than relying on the 5 Series architecture.

It still employs a four-link front suspension and a five-link rear axle, riding on 20-inch wheels and tyres.

It is expected to use the same suspension hardware as the M850i, right down to its variable electronically controlled dampers, adaptive power steering and limited-slip differential.

The coupe is 4843mm long and the Cabriolet will either shed or gain only single-digit millimetres from that figure, and will retain its 1902mm width. It is slated to lose some of the Coupe’s 420-litre boot capacity.

Inside, it uses the 8 Series Coupe’s 12.3-inch digital instrument cluster and stand-up 10.25-inch infotainment unit, while there are LED headlights and tail-lights.