The BMW 8 Series Gran Coupé is not just an 8 Series with an extra two doors: it is a distinct model with a bespoke vehicle dynamics setup. Ahead of the launch of the new car in September 2019, let’s take a look at what lies beneath that striking new body.
The Gran Coupé does of course share some DNA from the 8 Series Coupé and Convertible models, as well as the M8 GTE racing car. The latter has seen BMW M GmbH’s motor racing experience influence the chassis design and tuning, such as the torsion struts on the front axle and the shear panel incorporated on the rear axle, which optimise stiffness and the connection of suspension components to the body. Independent rubber bearings have been fitted to increase camber stiffness, while the damping plates at the rear axle further enhance the suspension’s dynamic baseline setup.
The coupe is fast too, right across the range, from the 530hp, 750Nm V8 M850i xDrive Gran Coupé (0- 62mph/100km/h in 3.9 seconds), to the six-cylinder, twin-turbo 320hp 680Nm diesel 840d xDrive (0- 62mph/100km/h in 5.1 seconds), to the 340hp, 500Nm petrol straight-six 840i (0- 62mph/100km/h in 5.2 seconds). All three variants feature an eight-speed Steptronic Sport transmission with paddleshifts as standard.
All-wheel drive is standard on the M850i xDrive and the 840d versions, while the 840i is rear-wheel-drive. The rear-biased xDrive intelligent all-wheel-drive system enables fully variable distribution of torque between the front and rear wheels to maximise traction and handling stability. Power is split using an electronically controlled multi-plate clutch networked with the powertrain and chassis systems.
An M Sport differential with active locking function at the rear axle is standard for the 840i and M850i xDrive and can be specified for the other model variants as part of the M Technic Sport Package. The electronically controlled rear differential lock limits optimises traction and power transfer on roads where grip levels vary between the left and right rear wheels, and also stops understeer or oversteer – without braking inputs – when driving through a quick succession of bends, or in situations involving multiple changes of direction and load.
Optimised aerodynamics and weight
The Gran Coupé is kept planted by an aerodynamics package that includes an almost completely sealed underbody, active air flap control with adjustable kidney grille slats, air curtains in the front apron and extra-thin exterior mirror bases. An additional front spoiler lip on the BMW M850i xDrive Gran Coupé minimises front-axle lift at high speeds.
Weight optimisation has been another key design consideration, with key measures including the use of an aluminium monocoque construction for the doors and the outer skin of the roof, with elements such as the bonnet, front shear panel, engine subframe, front bulkhead and rear bumper support also made from aluminium. The plastic boot lid, the magnesium cockpit support and the use of carbon fibre-reinforced plastic in the centre tunnel also help to reduce weight and optimise the distribution of that weight.
The result is a car that is the four-door is only 70kg heavier than the Coupé. That’s pretty respectable, given that the Gran Coupé has a 3,023mm wheelbase – 201mm longer than the two-door model, and while the front track width is the same as the coupe, at 1,627mm, the rear track is 28mm wider, at 1,671mm – the widest of any current BMW model.
The optional carbon-fibre roof further lowers the car’s centre of gravity, while a few negligible gains can be had from the ‘carbon package’, comprising air intake bars, exterior mirror caps and a rear diffuser insert, all made from CFRP.
Adaptive M suspension with bespoke tuning
While the suspension is similar to that of the two-door model, it has been tuned to match the specific dimensions and weight of the Gran Coupé. Standard specification includes Adaptive M suspension with electronically controlled dampers and extremely stiff springs which reduce body roll and allow the dampers to stabilise the wheels as much as possible and reduce traction loss caused by uneven surfaces.
The optional Adaptive M suspension Professional package also includes an active roll stabilisation feature, designed to optimise agility and directional stability on turn-in and to help line the car up for fast acceleration out of corners.
Integral Active Steering
Integral Active Steering is fitted as standard in the all-wheel-drive model variants and as an option for the 840i Gran Coupé. The system combines Servotronic speed-sensitive power assistance and a variable steering ratio at the front wheels with a steering rear axle. The rear wheels are steered differently, depending on the vehicle’s speed, turning in the opposite direction to the front wheels at speeds of up to 45mph and in the same direction at higher speeds.
Model-specific braking systems
All versions of the Gran Coupé have four-piston, fixed-caliper brakes at the front and single-piston, floating-caliper brakes at the rear. The electromechanical parking brake is integrated into the rear calipers. The optional M Sport package includes M Sport brakes with 374mm discs, while the M Technic Sport Package adds the 395mm brake discs fitted as standard on the M850i xDrive.
Wheels and tyres
The M850i features 20in M light-alloy wheels in a grey metallic finish, with high-performance tyres (front: 245/35 R20, rear: 275/30 R20) developed specifically for the 8 Series. The other models in the range also feature mixed-size tyres, with standard equipment including 18in light- alloy wheels fitted with 245/45 R18 tyres at the front and 275/40 R18 tyres at the rear. Models with the M Sport package ride on 19in M light-alloy wheels with 245/40 R19 tyres at the front and 275/35 R19 tyres at the rear, while the M Technic Sport Package upgrades to 20in light-alloy wheels and high-performance tyres.