The BMW 6 Series Convertible (F12 LCI), specifically the 640i variant with the Steptronic automatic transmission, represents a refined iteration of BMW’s luxury open-top grand tourer. Produced from 2015 to 2018, this facelifted version of the F12 generation brought updated styling, improved technology, and continued the 6 Series tradition of blending performance with open-air driving pleasure. Positioned as a mid-range offering within the 6 Series Convertible lineup, the 640i aimed to provide a balance between the more accessible 630i/635i models and the high-performance 650i. It served as a popular choice for buyers seeking a sophisticated and capable convertible without the outright expense of the flagship model.
Technical Specifications
| Brand | BMW |
| Model | 6 Series |
| Generation | 6 Series Convertible (F12 LCI, facelift 2015) |
| Type (Engine) | 640i (320 Hp) Steptronic |
| Start of production | 2015 |
| End of production | 2018 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Cabriolet |
| Seats | 4 |
| Doors | 2 |
| Fuel consumption (urban) | 10.6-11.0 l/100 km (22.2 – 21.4 US mpg, 26.6 – 25.7 UK mpg, 9.4 – 9.1 km/l) |
| Fuel consumption (extra urban) | 5.8-6.1 l/100 km (40.6 – 38.6 US mpg, 48.7 – 46.3 UK mpg, 17.2 – 16.4 km/l) |
| Fuel consumption (combined) | 7.6-7.9 l/100 km (30.9 – 29.8 US mpg, 37.2 – 35.8 UK mpg, 13.2 – 12.7 km/l) |
| CO2 emissions | 176-184 g/km |
| Fuel Type | Petrol (Gasoline) |
| Acceleration 0 – 100 km/h | 5.5 sec |
| Acceleration 0 – 62 mph | 5.5 sec |
| Acceleration 0 – 60 mph | 5.2 sec |
| Maximum speed | 250 km/h (155.34 mph) |
| Emission standard | Euro 6 |
| Weight-to-power ratio | 5.7 kg/Hp, 175.8 Hp/tonne |
| Weight-to-torque ratio | 4 kg/Nm, 247.3 Nm/tonne |
| Power | 320 Hp @ 5800-6000 rpm |
| Power per litre | 107.4 Hp/l |
| Torque | 450 Nm @ 1300-4500 rpm (331.9 lb.-ft. @ 1300-4500 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | N55B30A |
| Engine displacement | 2979 cm3 (181.79 cu. in.) |
| Number of cylinders | 6 |
| Engine configuration | Inline |
| Cylinder Bore | 84 mm (3.31 in.) |
| Piston Stroke | 89.6 mm (3.53 in.) |
| Compression ratio | 10.2:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Direct injection |
| Engine aspiration | Twin-power turbo, Intercooler |
| Engine oil capacity | 6.5 l (6.87 US qt | 5.72 UK qt) |
| Coolant | 9.3 l (9.83 US qt | 8.18 UK qt) |
| Kerb Weight | 1820 kg (4012.41 lbs.) |
| Max. weight | 2325 kg (5125.75 lbs.) |
| Max load | 505 kg (1113.33 lbs.) |
| Trunk (boot) space – minimum | 300 l (10.59 cu. ft.) |
| Trunk (boot) space – maximum | 350 l (12.36 cu. ft.) |
| Fuel tank capacity | 70 l (18.49 US gal | 15.4 UK gal) |
| Length | 4894 mm (192.68 in.) |
| Width | 1894 mm (74.57 in.) |
| Height | 1365 mm (53.74 in.) |
| Wheelbase | 2855 mm (112.4 in.) |
| Front track | 1600 mm (62.99 in.) |
| Rear (Back) track | 1665 mm (65.55 in.) |
| Ride height (ground clearance) | 123 mm (4.84 in.) |
| Drag coefficient (Cd) | 0.30 |
| Minimum turning circle (turning diameter) | 11.7 m (38.39 ft.) |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives the rear wheels of the vehicle. |
| Drive wheel | Rear wheel drive |
| Number of gears and type of gearbox | 8 gears, automatic transmission Steptronic |
| Front suspension | Double wishbone |
| Rear suspension | Independent multi-link suspension |
| Front brakes | Disc |
| Rear brakes | Disc |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Steering rack and pinion |
| Power steering | Electric Steering |
| Tires size | 225/55 R17; 245/45 R18; 275/45 R18; 245/40 R19; 275/35 R19; 245/35 R20; 275/30 R20 |
| Wheel rims size | 8J x 17; 8J x 18; 9J x 18; 8.5J x 19; 9J x 19; 8.5J x 20; 9J x 20 |
Powertrain & Engine Architecture
The heart of the 640i is BMW’s N55B30A, a 3.0-liter inline-six cylinder engine. This engine is a direct-injection, twin-turbocharged powerplant known for its smooth power delivery and responsiveness. The N55 utilizes Valvetronic technology, which allows for stepless control of valve lift, optimizing both power and efficiency. The twin-turbo setup employs a single twin-scroll turbocharger, enhancing low-end torque and minimizing turbo lag. The engine produces 320 horsepower at 5800-6000 rpm and 450 Nm (331.9 lb-ft) of torque between 1300 and 4500 rpm. Paired with the engine is BMW’s 8-speed Steptronic automatic transmission. This transmission offers both fully automatic operation and manual gear selection via steering wheel-mounted paddles. The Steptronic transmission is programmed for smooth shifts and quick response, contributing to the overall driving experience.
Driving Characteristics
The 640i Steptronic delivers a refined and comfortable driving experience. While not as aggressively tuned as the 650i, the 320 hp engine provides ample power for spirited driving. Acceleration from 0 to 60 mph takes approximately 5.2 seconds. The Steptronic transmission contributes to smooth and seamless gear changes, enhancing the sense of effortless performance. Compared to the 650i, the 640i offers a slightly less visceral experience, but its lighter weight and more balanced chassis contribute to agile handling. The automatic transmission, while convenient, doesn’t offer the same level of driver engagement as the available manual transmission. Gear ratios are optimized for a blend of acceleration and fuel efficiency, with taller gearing in higher gears for relaxed cruising.
Equipment & Trim Levels
The 640i Convertible came standard with a generous array of features, including leather upholstery, power-adjustable seats with memory function, a premium sound system, automatic climate control, and BMW’s iDrive infotainment system with a central display screen. Optional extras included features like active steering, adaptive suspension, a head-up display, and various interior trim options. The soft top was fully automatic and could be raised or lowered in approximately 24 seconds. Interior trim options ranged from standard wood veneers to more luxurious carbon fiber accents. Exterior styling cues included chrome accents and distinctive LED lighting.
Chassis & Braking
The F12 6 Series Convertible features a double-wishbone front suspension and an independent multi-link rear suspension. This setup provides a comfortable ride while maintaining precise handling. The 640i typically came equipped with disc brakes on all four wheels, providing ample stopping power. Anti-lock braking system (ABS) and electronic stability control (ESC) were standard safety features. The chassis was designed to minimize weight and maximize rigidity, contributing to the car’s overall handling characteristics. The steering system is a rack-and-pinion setup with electric power assistance.
Market Reception & Comparison
The 640i Convertible was generally well-received by automotive critics. It was praised for its refined driving experience, luxurious interior, and stylish design. Compared to the 650i, the 640i offered a more accessible price point without sacrificing too much performance. Fuel economy was considered respectable for a vehicle in this class, with combined fuel consumption figures ranging from 7.6 to 7.9 l/100 km. Reliability was generally good, although some owners reported minor issues with the electronic systems. The 640i positioned itself as a strong competitor to other luxury convertibles, such as the Mercedes-Benz E-Class Cabriolet and the Audi A5 Cabriolet.
Legacy
The BMW 640i Convertible (F12 LCI) remains a desirable used car today. The N55 engine is known for its durability and relatively straightforward maintenance. While the car is no longer in production, it continues to appeal to buyers seeking a stylish and capable luxury convertible. The Steptronic transmission has proven to be reliable, although regular maintenance is essential. The F12 6 Series Convertible represents a high point in BMW’s convertible design and engineering, offering a compelling blend of performance, luxury, and open-air driving enjoyment.
