The BMW 4 Series Convertible (F33), specifically the 420i variant produced from 2017 to 2020 following the facelift, represents a compelling entry point into the premium mid-size convertible market. Positioned as the base engine option within the F33 lineup, the 420i offered a balance of performance, efficiency, and affordability compared to its more powerful siblings like the 430i and 440i. This model year saw updates to the styling, technology, and engine options, solidifying the F33’s position as a desirable open-top grand tourer. The 420i catered to buyers seeking the style and driving experience of a BMW convertible without the higher price tag associated with the range-topping models.
Technical Specifications
| Brand | BMW |
| Model | 4 Series |
| Generation | 4 Series Convertible (F33, facelift 2017) |
| Type (Engine) | 420i (184 Hp) |
| Start of production | 2017 |
| End of production | 2020 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Cabriolet |
| Seats | 4 |
| Doors | 2 |
| Fuel consumption (urban) | 8.0-8.6 l/100 km (29.4 – 27.4 US mpg) |
| Fuel consumption (extra urban) | 5.1-5.5 l/100 km (46.1 – 42.8 US mpg) |
| Fuel consumption (combined) | 6.2-6.6 l/100 km (37.9 – 35.6 US mpg) |
| CO2 emissions | 145-153 g/km |
| Fuel Type | Petrol (Gasoline) |
| Acceleration 0 – 100 km/h | 8.2 sec |
| Acceleration 0 – 62 mph | 8.2 sec |
| Acceleration 0 – 60 mph | 7.8 sec |
| Maximum speed | 230 km/h (142.92 mph) |
| Emission standard | Euro 6 |
| Weight-to-power ratio | 9.2 kg/Hp, 108.2 Hp/tonne |
| Weight-to-torque ratio | 5.9 kg/Nm, 170.6 Nm/tonne |
| Power | 184 Hp @ 5000 rpm |
| Torque | 290 Nm @ 1350-4600 rpm (213.89 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 | 7.8 l (8.24 US qt | 6.86 UK qt) |
| Kerb Weight | 1700 kg (3747.86 lbs.) |
| Max. weight | 2170 kg (4784.03 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%) | 1400 kg (3086.47 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 (Back) track | 1593 mm (62.72 in.) |
| Ride height (ground clearance) | 130 mm (5.12 in.) |
| Drag coefficient (Cd) | 0.30 |
| Minimum turning circle (turning diameter) | 11.3 m (37.07 ft.) |
| Drivetrain Architecture | Rear wheel drive |
| Drive wheel | Rear wheel drive |
| Number of gears and type of gearbox | 6 gears, manual transmission |
| 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 |
Powertrain & Engine Architecture
The heart of the 420i Convertible is BMW’s B48B20A 2.0-liter turbocharged inline-four cylinder engine. This engine is a member of BMW’s modular engine family, known for its efficiency and responsiveness. The B48 utilizes direct fuel injection, a single twin-scroll turbocharger, and variable valve timing (Valvetronic) and variable camshaft timing (Double VANOS) to optimize performance and fuel economy. The engine produces 184 horsepower at 5,000 rpm and 290 Nm (213.89 lb-ft) of torque between 1,350 and 4,600 rpm. The engine’s relatively flat torque curve provides good drivability in various conditions. The 420i was typically paired with a six-speed manual transmission, although an optional eight-speed automatic transmission (ZF 8HP) was also available. The automatic transmission offered smoother shifts and enhanced convenience, but at the expense of some driver engagement.
Driving Characteristics
The 420i Convertible, while not the quickest variant in the 4 Series range, provides a pleasant and engaging driving experience. Acceleration from 0 to 60 mph takes approximately 7.8 seconds, and the car has a top speed of 142.92 mph. The engine delivers adequate power for everyday driving and highway cruising. The automatic transmission, when equipped, offers quick and precise shifts, contributing to a refined driving experience. However, compared to the 430i or 440i, the 420i feels less eager to accelerate and may require more downshifting when overtaking. The rear-wheel-drive configuration provides a balanced chassis and predictable handling, making the 420i a fun car to drive on winding roads.
Equipment & Trim Levels
The 420i Convertible came standard with a generous array of features, including leatherette upholstery, automatic climate control, a 6.5-inch iDrive infotainment system, and a power-operated soft top. Optional extras included leather upholstery, a premium sound system, navigation, heated seats, and parking sensors. Trim levels were relatively simple, with most options being added individually. The focus was on providing a comfortable and well-equipped convertible experience without the extensive customization options found in higher-end models.
Chassis & Braking
The F33 4 Series Convertible utilizes a sophisticated chassis design featuring an independent suspension at all four corners. The front suspension consists of coil springs and struts, while the rear suspension employs a multi-link setup. This configuration provides a good balance of ride comfort and handling precision. The 420i typically came equipped with ventilated disc brakes on all four wheels, providing ample stopping power. Anti-lock braking system (ABS) and electronic stability control (ESC) were standard safety features.
Market Reception & Comparison
The 420i Convertible was generally well-received by automotive critics as an accessible entry point into the 4 Series range. It was praised for its stylish design, comfortable interior, and engaging driving dynamics. However, some critics noted that the engine lacked the outright performance of its more powerful siblings. Compared to the 430i, the 420i offered lower running costs and a more affordable price tag, making it an attractive option for buyers prioritizing value. The 420i also offered better fuel economy than the higher-output models, with combined fuel consumption ranging from 37.9 to 35.6 US mpg.
Legacy
The BMW 420i Convertible (F33) has proven to be a relatively reliable vehicle, with the B48 engine generally considered robust. Common issues are typically related to the cooling system and oil leaks, but these are not widespread. On the used car market, the 420i Convertible represents a good value proposition for buyers seeking a stylish and well-equipped convertible. Its lower price point and reasonable running costs make it an attractive alternative to more expensive premium convertibles. The F33 4 Series Convertible, including the 420i variant, continues to be a popular choice among enthusiasts and casual drivers alike.
