First drive: the new BMW 7-Series

This new 7-series is a wildly important car for BMW. That's not immediately obvious. After all, the blue and white badge probably conjures thoughts of a well-specced 3-series or maybe an M5.

But the brand-new 7-er matters. Not only because it's their flagship, the best they can do, but also because it's the launchpad for a complete renewal of all the 'conventional' BMWs - everything except the small FWD series, and the i cars.

So the prototype 740iL I'm driving isn't just a limo for Florida cosmetic surgeons and young Chinese entrepreneurs. It's a window into the future of BMW.

And they've thrown the kitchen sink at it. An all-new straight-six. Totally new monocoque. All-new suspension and brakes. The seats. The air-conditioning. They could have carried all of this over - what they had was fine really. But they took the opportunity to go right through it all and make it better. And, vitally, lighter too.

Truth be told, from the look of the swirly-disguised prototype I'm driving, there might be a bit of disappointment when we see the final styling. It looks like a fairly conservative evolution, which is doubtless what the buyers want.

The diet has been especially rigorous on the 7-series, because they have applied knowledge from the i3 and i8 to build a body shell that uses significant amounts of carbon fibre. The perimeter of the roof, the pillars, the sills and transmission tunnel, they're all made stronger and significantly lighter by clever carbon bracing.

You can't see this in the finished car. It's all painted over. All buyers will have to show for it is a medallion inside the door opening that says 'carbon core'. But they'll feel the extra solid strength and the benefits of lightness.

A new six-cylinder 7-series is about 130kg lighter than before. In fact the engineers had to make about 200kg of savings to get to this figure, because there is about 70kg of extra equipment. So the starting kerb weight is about 1770kg.

Much of the prototype's interior is obscured by crude felt curtains. But I can see it has changed by having all-new switches, many of them brushed metal like the new-generation Mercedes items. And the redesign of the display and control systems makes it feel fresh.

This 740iL has a turbo straight-six, but it's completely different from the one in current six-cylinder BMWs. It's in the same modular family as the Mini and i8 three-cylinder, and the new fours just being introduced. It makes about 330bhp (they're officially being coy) and is lighter and more efficient than the already excellent engine in the current 7-series. At medium rpm it's responsive, seldom showing much turbo lag. The prototype I'm driving sometimes shifts gear abruptly, but BMW normally fixes such things before full production. It's also very quiet in the mid-ranges. But as you bring it towards the red-line, there's a gradual change in character, with a new life in performance and eagerness and a surprising engagement with you.

The chassis has the same dual-sided nature. It integrates several adaptive systems. Air suspension is standard on all cars, which is self-levelling, and can lower itself for faster, sportier driving. It works with standard adaptive dampers.

Our test car added had two options: rear-wheel steering, and adaptive roll stabilisation. The roll stabilisation uses electromechanical actuators to twist the anti-roll bars and reduce cornering roll. The rear steering adds agility at low speed by going in the opposite direction to the fronts. At speed it goes the same way, for stability. The 7 had both these before, but they're redesigned, and actuated electrically not hydraulically, which makes them quicker-witted and more efficient.

But the real cleverness is the control and integration. For instance, the processors read the upcoming road from the navigation, and set the car up for corners. If the road ahead is straight, it'll relax the chassis. Of course it also tailors itself to the way you're driving.

Never mind the digital wizardry, it feels amazingly natural. For a big barge it feels light-footed and amazingly natural. The steering is fairly light for gentle inputs but extremely progressive. At any speed, it's easy to pour it into a corner in one liquid-smooth motion. Body movements are tidy and well-damped.

Push on a bit and it still keeps good control of roll and stays tidy. But as BMW's head of development Klaus Fröhlich said to me, "This car isn't about driving at maximum g. You don't need to go fast to feel how precise the car is. It always behaves absolutely predictably. That's what fun to drive is about in this car." True enough, and it shows how the BMW engineers have kept in mind the way buyers of big saloons generally drive.

This precision hasn't been bought at the expense of full-on luxo-barge comfort. The air suspension is very supple over all sorts of bumps, and because there's no anti-roll in a straight line, you aren't rocked from side to side when only the left or right wheels hit a bump. "We wanted people in the back to be able to write on their iPads while you drive," an engineer tells me.

For the one at the wheel, the other big news is the extended iDrive system. The main screen is now touch-sensitive, so you can interact with it like a tablet or smartphone. But if that doesn't suit you, all the same functions can be done by the rotary controller too. There's better voice activation, but they acknowledge you look a divot talking to your car while there are other passengers, so again it's redundant with the controller wheel.

Finally it introduces gesture control. You don't even need to touch the screen: if a phone call comes in, you just point in the general direction of the screen to answer. If you want to reject the call, wave your arm horizontally away from you as if dismissing a bad idea. You can spiral your finger in the air to increase stereo volume, and a two-finger jab (a sort of horizontal eff-off) can be configured to do one of a choice several things like navigate you home or switch to a fave radio station. A camera by the rear-view mirror sees your fingers and a visual processor interprets them. But to be honest it's mostly a gimmick so far - twisting your fingers in the air is more cumbersome than just turning the actual volume knob.

The new body construction is far from a gimmick. Its crash resistance is better than ever, and its stiffness brings benefits to ride and handling, and its lightness has allowed a useful downward weight spiral in the rest of the car: suspension and braking loads are lower, so those parts can be reduced in mass too. Most striking is the use of carbon fibre, in quantities unique for a mass-made car. It's possible because of techniques and production methods devised for the i3 and i8.

Various types of carbon are used for almost the whole roof perimeter and cross-braces, all the pillars, sills and tunnel top. The roof side bows are a lever woven pipe, a bit like what's in the Lexus LFA. Unique AFAIK is the B-post construction, bonded double-layer of carbon fibre and high-strength steel. Carbon alone is very strong but can shatter at extreme loads. The steel allows bending instead.

The doors and most of the exterior panels are aluminium, and there are cast aluminium parts for the suspension domes and the front and rear crash rails. The non-ferrous total is completed by an elaborate magnesium cross-car beam for the dashboard and steering column support. All of which gives a body some 40kg lighter than the current 7-series'.

The engineers also set about saving weight in many other places, but especially, in pursuit of better dynamics, in the unsprung parts of the chassis. So it has all-aluminium six-piston brake calipers, discs with iron friction surfaces by aluminium centres, lightweight hub carriers and re-shaped arms. In all some 35kg of unsprung mass has been lost. That will have huge benefits in ride and handling on bumpy roadways.

Then there's a lighter exhaust system, a lighter air-conditioning system, lighter seats, and lighter doors. Even the engine gets attention: it's not only lighter in itself by 9kg, but it's closely wrapped in a dense foam 'acoustic capsule' so that the overall amount of sound insulation in the whole engine-bay could be reduced.

Being German and pricey, the new 7 is inevitably surrounded by sensors to find other traffic and pedestrians and cyclists, and make sure you don't collide with them. The 7-series can also follow other traffic by radar, or its own lane by visual cameras, to give you highly automated speed control and steering support at speeds from a standstill to 130mph. Most of these are similar, naturally, to Mercedes' offerings. But BMW adds some clever wrinkles, including a simple one-tap button to change speed to obey each sign you pass.

Another flourish is that it will drive just over its own length with no-one inside. Sounds pointless I know. But if you need to park in a bay or garage that's too narrow for you to open the door, you can point the car at the bay, then get out completely, and it will then guide itself in, stop the engine and lock itself. You stand by pressing a button on the key fob. And you can reverse the process, starting it remotely and watching it motor autonomously out far enough for you to open the door and drive off.

Obviously BMW will be expecting videos of that to go viral. Same with the gesture control. But what really matters with the new 7 is the fundamental soundness of the basic body, and the new generation of running gear that will underpin so many BMWs. As far as this shortish drive shows, Munich's expertise in those fields is intact.