The BMW 4 Series Convertible (F33), specifically the 420i Steptronic model produced from 2017 to 2020, represents a mid-cycle refresh of the F33 generation. This variant occupied a key position in the 4 Series lineup, serving as the entry point to the convertible experience while still offering a premium BMW driving experience. Positioned below the more powerful 430i and 440i models, the 420i Steptronic aimed for a balance between affordability, fuel efficiency, and respectable performance. It was primarily marketed towards buyers seeking a stylish, open-top vehicle for comfortable cruising rather than outright sports car thrills.
Technical Specifications
| Brand | BMW |
| Model | 4 Series |
| Generation | 4 Series Convertible (F33, facelift 2017) |
| Type (Engine) | 420i (184 Hp) Steptronic |
| Start of production | 2017 |
| End of production | 2020 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Cabriolet |
| Seats | 4 |
| Doors | 2 |
| Fuel consumption (urban) | 7.6-8.1 l/100 km (30.9 – 29 US mpg, 37.2 – 34.9 UK mpg, 13.2 – 12.3 km/l) |
| Fuel consumption (extra urban) | 4.8-5.1 l/100 km (49 – 46.1 US mpg, 58.9 – 55.4 UK mpg, 20.8 – 19.6 km/l) |
| Fuel consumption (combined) | 5.8-6.2 l/100 km (40.6 – 37.9 US mpg, 48.7 – 45.6 UK mpg, 17.2 – 16.1 km/l) |
| CO2 emissions | 136-144 g/km |
| Fuel Type | Petrol (Gasoline) |
| Acceleration 0 – 100 km/h | 8.4 sec |
| Acceleration 0 – 62 mph | 8.4 sec |
| Acceleration 0 – 60 mph | 8 sec (Calculated) |
| Maximum speed | 230 km/h (142.92 mph) |
| Emission standard | Euro 6 |
| Weight-to-power ratio | 9.3 kg/Hp, 107.3 Hp/tonne |
| Weight-to-torque ratio | 6.4 kg/Nm, 157.4 Nm/tonne |
| Power | 184 Hp @ 5000 rpm |
| Torque | 270 Nm @ 1350-4600 rpm (199.14 lb.-ft. @ 1350-4600 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | B48B20A |
| Engine displacement | 1998 cm3 (121.93 cu. in.) |
| Number of cylinders | 4 |
| Engine configuration | Inline |
| Cylinder Bore | 82 mm (3.23 in.) |
| Piston Stroke | 94.6 mm (3.72 in.) |
| Compression ratio | 11:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Direct injection |
| Engine aspiration | Twin-power turbo, Intercooler |
| Engine oil capacity | 5 l (5.28 US qt | 4.4 UK qt) |
| Coolant capacity | 8.1 l (8.56 US qt | 7.13 UK qt) |
| Kerb Weight | 1715 kg (3780.93 lbs.) |
| Max. weight | 2185 kg (4817.1 lbs.) |
| Max load | 470 kg (1036.17 lbs.) |
| Trunk (boot) space – minimum | 370 l (13.07 cu. ft.) |
| Fuel tank capacity | 60 l (15.85 US gal | 13.2 UK gal) |
| Permitted trailer load with brakes (12%) | 1500 kg (3306.93 lbs.) |
| Permitted trailer load without brakes | 695 kg (1532.21 lbs.) |
| Permitted towbar download | 75 kg (165.35 lbs.) |
| Length | 4640 mm (182.68 in.) |
| Width | 1825 mm (71.85 in.) |
| Height | 1384 mm (54.49 in.) |
| Wheelbase | 2810 mm (110.63 in.) |
| Front track | 1544 mm (60.79 in.) |
| Rear track | 1593 mm (62.72 in.) |
| Ride height (ground clearance) | 130 mm (5.12 in.) |
| Drag coefficient (Cd) | 0.30 |
| Minimum turning circle | 11.3 m (37.07 ft.) |
| Drivetrain Architecture | Rear wheel drive |
| Number of gears and type of gearbox | 8 gears, automatic transmission Steptronic |
| Front suspension | Independent coil spring |
| Rear suspension | Independent multi-link suspension |
| Front brakes | Ventilated discs |
| Rear brakes | Ventilated discs |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Steering rack and pinion |
| Power steering | Electric Steering |
| Tires size | 225/50 R17; 225/45 R18; 255/40 R18; 225/40 R19; 255/35 R19 |
| Wheel rims size | 7.5J x 17; 8J x 18; 8.5J x 18; 8J x 19; 8.5J x 19 |
INTRODUCTION
The F33 420i Steptronic, introduced with the 2017 facelift, built upon the foundation of the original F33 4 Series Convertible launched in 2013. The facelift brought subtle styling revisions, updated technology, and improvements to the engine range. This particular variant utilized BMW’s B48 engine family, paired with their 8-speed Steptronic automatic transmission. The 420i aimed to provide a more accessible entry point into the 4 Series Convertible range, appealing to buyers who prioritized comfort and style over outright performance. It competed with other premium convertibles like the Audi A3 Cabriolet and Mercedes-Benz C-Class Cabriolet.
Powertrain & Engine Architecture
At the heart of the 420i Steptronic lies the B48B20A 2.0-liter inline-four cylinder engine. This engine is a member of BMW’s modular engine family, known for its efficiency and refinement. It features direct fuel injection, a single twin-scroll turbocharger, and variable valve timing (VANOS) on both the intake and exhaust sides. The B48 engine produces 184 horsepower at 5000 rpm and 270 Nm (199 lb-ft) of torque between 1350 and 4600 rpm. The 8-speed Steptronic automatic transmission is a torque-converter type, offering smooth and quick shifts. It features a wide gear ratio spread, contributing to both fuel efficiency and responsive acceleration. The transmission can be operated in Drive, Sport, and Manual modes, allowing the driver to tailor the driving experience.
Driving Characteristics
The 420i Steptronic delivers a comfortable and refined driving experience. While not as dynamically engaging as the higher-powered 4 Series variants, it provides sufficient power for everyday driving and relaxed cruising. The 8-speed automatic transmission is well-matched to the engine, providing smooth gear changes and keeping the engine within its optimal power band. Acceleration from 0 to 60 mph takes approximately 8 seconds. The Steptronic transmission’s programming prioritizes fuel efficiency, resulting in slightly slower shifts compared to the more aggressive settings found in the 430i and 440i. The rear-wheel-drive configuration contributes to balanced handling, although it doesn’t offer the same level of grip as all-wheel-drive models.
Equipment & Trim Levels
The 420i Steptronic came standard with a comprehensive list of features, including leatherette upholstery, automatic climate control, a 6.5-inch iDrive infotainment system, and rear parking sensors. Optional extras included leather upholstery, a larger iDrive screen with navigation, a Harman Kardon sound system, and various driver-assistance features such as lane departure warning and adaptive cruise control. The interior design was typical BMW, with a focus on quality materials and a driver-centric layout. Trim levels were relatively simple, with most customization options available through individual selections rather than distinct packages.
Chassis & Braking
The 420i Convertible utilizes a MacPherson strut front suspension and a multi-link rear suspension, providing a comfortable ride and good handling characteristics. The suspension is tuned for comfort, prioritizing ride quality over outright sportiness. Brakes consist of ventilated discs on all four wheels, providing adequate stopping power. ABS (Anti-lock Braking System) is standard. The steering is electrically assisted, offering precise and responsive control. The 420i’s weight of approximately 1715 kg (3780 lbs) is relatively moderate for a convertible, contributing to its balanced handling.
Market Reception & Comparison
The 420i Steptronic was generally well-received by automotive critics. It was praised for its comfortable ride, refined engine, and stylish design. However, some reviewers noted that it lacked the performance and engagement of the higher-powered 4 Series variants. Compared to the 430i, the 420i offered significantly less power and acceleration. The 430i’s six-cylinder engine provided a more exhilarating driving experience, but at a higher price point. In terms of fuel economy, the 420i offered a slight advantage over the 430i and 440i. Reliability reports suggest that the B48 engine is generally reliable, although some owners have reported issues with the cooling system and oil leaks.
Legacy
The F33 420i Steptronic remains a popular choice in the used car market. Its combination of style, comfort, and affordability makes it an attractive option for buyers seeking a premium convertible. The B48 engine has proven to be a durable and reliable unit, although regular maintenance is essential. As with any used vehicle, potential buyers should carefully inspect the car for any signs of wear and tear, and obtain a pre-purchase inspection from a qualified mechanic. The F33 generation 4 Series Convertible, including the 420i, represents a significant step forward in BMW’s convertible design and engineering, offering a compelling blend of luxury, performance, and open-air enjoyment.
