The BMW 4 Series Convertible (G23) M440d xDrive Steptronic is a grand touring convertible produced by the German automaker BMW from November 2021 to January 2024. Positioned as a premium offering within the G23 4 Series Convertible range, the M440d combines a potent diesel engine with mild-hybrid technology and all-wheel drive. It represents BMW’s commitment to blending performance, efficiency, and open-air driving enjoyment. This variant aimed to appeal to buyers seeking a refined and powerful convertible experience without sacrificing fuel economy.
Technical Specifications
| Brand | BMW |
| Model | 4 Series |
| Generation | 4 Series Convertible (G23) |
| Type | M440d (340 Hp) Mild Hybrid xDrive Steptronic |
| Start of production | November, 2021 |
| End of production | January, 2024 |
| Powertrain Architecture | MHEV (Mild Hybrid Electric Vehicle) |
| Body type | Cabriolet |
| Seats | 4 |
| Doors | 2 |
| Fuel consumption at Low speed (WLTP) | 10.1-10.6 l/100 km (23.3 – 22.2 US mpg) |
| Fuel consumption at Medium speed (WLTP) | 5.9-6.4 l/100 km (39.9 – 36.8 US mpg) |
| Fuel consumption at high speed (WLTP) | 5-5.5 l/100 km (47 – 42.8 US mpg) |
| Fuel consumption at very high speed (WLTP) | 5.4-6.1 l/100 km (43.6 – 38.6 US mpg) |
| Combined fuel consumption (WLTP) | 6-6.6 l/100 km (39.2 – 35.6 US mpg) |
| CO2 emissions (WLTP) | 157-172 g/km |
| Fuel Type | Diesel |
| Acceleration 0 – 100 km/h | 5 sec |
| Acceleration 0 – 62 mph | 5 sec |
| Acceleration 0 – 60 mph | 4.8 sec |
| Maximum speed | 250 km/h (155.34 mph) |
| Emission standard | Euro 6d |
| Weight-to-power ratio | 5.8 kg/Hp |
| Weight-to-torque ratio | 2.8 kg/Nm |
| Gross battery capacity | 0.4 kWh |
| Battery voltage | 48 V |
| Battery technology | Lithium-ion (Li-Ion) |
| Battery location | Under the front hood |
| Electric motor power | 11 Hp |
| Electric motor Torque | 25 Nm (18.44 lb.-ft.) |
| Electric motor location | Front, Longitudinal |
| Power | 340 Hp @ 4400 rpm |
| Torque | 700 Nm @ 1750-2250 rpm (516.29 lb.-ft. @ 1750-2250 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | B57D30B |
| Engine displacement | 2993 cm3 (182.64 cu. in.) |
| Number of cylinders | 6 |
| Engine configuration | Inline |
| Cylinder Bore | 84 mm (3.31 in.) |
| Piston Stroke | 90 mm (3.54 in.) |
| Compression ratio | 16.5:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Diesel Commonrail |
| Engine aspiration | Twin-power turbo, Intercooler |
| Valvetrain | DOHC |
| Engine oil capacity | 7 l (7.4 US qt | 6.16 UK qt) |
| Coolant | 7.7 l (8.14 US qt | 6.78 UK qt) |
| Kerb Weight | 1980 kg (4365.15 lbs.) |
| Max. weight | 2480 kg (5467.46 lbs.) |
| Max load | 500 kg (1102.31 lbs.) |
| Trunk (boot) space – minimum | 300 l (10.59 cu. ft.) |
| Trunk (boot) space – maximum | 385 l (13.6 cu. ft.) |
| Fuel tank capacity | 59 l (15.59 US gal | 12.98 UK gal) |
| Permitted trailer load with brakes (8%) | 1800 kg (3968.32 lbs.) |
| Permitted trailer load with brakes (12%) | 1800 kg (3968.32 lbs.) |
| Permitted trailer load without brakes | 750 kg (1653.47 lbs.) |
| Length | 4768 mm (187.72 in.) |
| Width | 1852 mm (72.91 in.) |
| Width including mirrors | 2081 mm (81.93 in.) |
| Height | 1384 mm (54.49 in.) |
| Wheelbase | 2851 mm (112.24 in.) |
| Front track | 1573 mm (61.93 in.) |
| Rear (Back) track | 1612 mm (63.46 in.) |
| Front overhang | 858 mm (33.78 in.) |
| Rear overhang | 1059 mm (41.69 in.) |
| Minimum turning circle | 12 m (39.37 ft.) |
| Drivetrain Architecture | ICE and electric motor drive all four wheels |
| Drive wheel | All wheel drive (4×4) |
| Number of gears | 8 |
| Gearbox type | Automatic transmission Steptronic |
| Front suspension | Spring Strut, Transverse stabilizer |
| Rear suspension | Independent multi-link spring suspension with stabilizer |
| Front brakes | Ventilated discs |
| Rear brakes | Ventilated discs |
| Steering type | Steering rack and pinion |
| Power steering | Electric Steering |
| Tires size (Front) | 225/45 R18; 225/40 R19 |
| Tires size (Rear) | 250/40 R18; 255/35 R19 |
| Wheel rims size (Front) | 7.5J x 18; 8J x 19 |
| Wheel rims size (Rear) | 8.5J x 18; 8.5J x 19 |
INTRODUCTION
The BMW 4 Series Convertible (G23) M440d xDrive Steptronic, launched in November 2021, represents the third generation of BMW’s 4 Series convertible. Built on the G23 platform, which shares its underpinnings with the 3 Series (G20), the M440d is a performance-oriented variant distinguished by its powerful diesel engine and mild-hybrid assistance. It aimed to provide a luxurious and engaging driving experience in a stylish, open-top package. Production continued until January 2024, making it a relatively short-lived but significant model within the 4 Series lineup.
Powertrain & Engine Architecture
At the heart of the M440d lies the BMW B57D30B 3.0-liter inline-six diesel engine. This engine is a sophisticated unit featuring a twin-turbocharger setup and a common-rail direct fuel injection system. The B57 engine family is renowned for its robust construction and high torque output. The ‘D30B’ designation indicates a specific iteration optimized for performance. The mild-hybrid system, utilizing a 48V lithium-ion battery and an integrated starter generator, provides a power boost during acceleration and enables smoother start-stop operation, improving fuel efficiency. The engine produces 340 horsepower at 4400 rpm and a substantial 700 Nm (516 lb-ft) of torque between 1750 and 2250 rpm. This power is delivered to all four wheels via BMW’s xDrive all-wheel-drive system and an eight-speed Steptronic automatic transmission. The Steptronic transmission offers both automatic shifting and manual control via steering wheel-mounted paddles.
Driving Characteristics
The M440d xDrive Steptronic delivers a compelling driving experience characterized by strong acceleration and confident handling. The combination of the powerful diesel engine and the all-wheel-drive system allows for a 0-60 mph time of around 4.8 seconds. The eight-speed automatic transmission is well-tuned, providing smooth and responsive gear changes. While not as overtly sporty as the M4 convertible, the M440d offers a refined and capable driving experience suitable for long-distance cruising and spirited driving alike. The mild-hybrid system contributes to a seamless power delivery, minimizing turbo lag and enhancing responsiveness. Compared to the 420d or 430d models, the M440d offers a significant performance upgrade, while remaining more fuel-efficient than the gasoline-powered M440i.
Equipment & Trim Levels
The M440d xDrive Steptronic came generously equipped as standard. Interior features typically included leather upholstery, power-adjustable sports seats, a premium sound system, and BMW’s iDrive infotainment system with a large touchscreen display. Standard safety features included automatic emergency braking, lane departure warning, and adaptive cruise control. Optional extras included a head-up display, ventilated seats, a glass roof, and various customization options for interior trim and exterior styling. The M Sport package was a popular option, adding more aggressive styling cues and sport-tuned suspension components.
Chassis & Braking
The G23 4 Series Convertible features a sophisticated chassis designed to balance comfort and handling. The front suspension utilizes a spring strut design with a transverse stabilizer, while the rear suspension employs an independent multi-link setup, also with a stabilizer bar. The M440d typically featured larger brakes than the lower-trim models, with ventilated discs at all four corners. The xDrive all-wheel-drive system intelligently distributes torque between the front and rear axles, optimizing traction and stability in various driving conditions. The steering is precise and well-weighted, providing good feedback to the driver.
Market Reception & Comparison
The M440d xDrive Steptronic was generally well-received by automotive critics. Reviewers praised its powerful engine, refined ride quality, and luxurious interior. The fuel economy was also noted as a strong point, particularly considering the car’s performance capabilities. Compared to the gasoline-powered M440i, the M440d offered a more economical option without sacrificing a significant amount of performance. However, some critics noted that the diesel engine lacked the aural excitement of the gasoline counterpart. Against competitors like the Audi A5 Cabriolet and Mercedes-Benz C-Class Cabriolet, the M440d held its own, offering a compelling combination of performance, luxury, and technology.
Legacy
The BMW 4 Series Convertible (G23) M440d xDrive Steptronic, despite its relatively short production run, represents a significant offering in BMW’s convertible lineup. The B57 diesel engine is known for its durability and reliability, and the mild-hybrid system adds a layer of efficiency and refinement. On the used car market, these models are sought after by buyers looking for a powerful and comfortable convertible with good fuel economy. Properly maintained examples are expected to remain reliable for many years, making the M440d a desirable option for enthusiasts and everyday drivers alike.
