The BMW i8 Roadster (I15), produced from November 2017 to September 2018, represents BMW’s foray into the premium plug-in hybrid sports car market. Positioned as the open-top variant of the i8 coupe, it aimed to deliver a thrilling driving experience with significantly reduced emissions. Built on the i8 platform (UX0/I15), the Roadster combined a compact three-cylinder turbocharged gasoline engine with an electric motor, offering all-wheel drive capability and a blend of performance and efficiency. It served as a halo vehicle, showcasing BMW’s commitment to innovative technology and sustainable mobility.
Technical Specifications
| Brand | BMW |
| Model | i8 |
| Generation | i8 Roadster (I15) |
| Type (Engine) | 1.5/11.6 kWh (374 Hp) xDrive Automatic |
| Start of production | November, 2017 |
| End of production | September, 2018 |
| Powertrain Architecture | PHEV (Plug-in Hybrid Electric Vehicle) |
| Body type | Roadster |
| Seats | 2 |
| Doors | 2 |
| Fuel consumption (economy) – combined (NEDC) | 2 l/100 km (117.6 US mpg, 141.2 UK mpg, 50 km/l) |
| CO2 emissions (NEDC) | 46 g/km |
| Fuel Type | Petrol / electricity |
| Acceleration 0 – 100 km/h | 4.6 sec |
| Acceleration 0 – 62 mph | 4.6 sec |
| Acceleration 0 – 60 mph | 4.4 sec |
| Maximum speed | 250 km/h (155.34 mph) – Electronically limited |
| Emission standard | Euro 6 |
| Weight-to-power ratio | 4.3 kg/Hp, 234.5 Hp/tonne |
| Weight-to-torque ratio | 2.8 kg/Nm, 357.4 Nm/tonne |
| Gross battery capacity | 11.6 kWh |
| Net (usable) battery capacity | 9.4 kWh |
| Battery voltage | 355 V |
| Battery technology | Lithium-ion (Li-Ion) |
| Battery location | In the central tunnel |
| Recuperation output | 60 kW |
| All-electric range (NEDC) | 53 km (32.93 mi) |
| Average Energy consumption (NEDC) | 14.5 kWh/100 km (23.34 kWh/100 mi, 144 MPGe, 6.9 km/kWh, 4.3 mi/kWh) |
| Max speed (electric) | 120 km/h (74.56 mph) |
| Electric motor power | 143 Hp @ 4800 rpm |
| Electric motor Torque | 250 Nm @ 0 rpm (184.39 lb.-ft.) |
| Electric motor location | Front axle, Transverse |
| System power | 374 Hp |
| System torque | 570 Nm (420.41 lb.-ft.) |
| Power | 231 Hp @ 5800 rpm |
| Torque | 320 Nm @ 3700 rpm (236.02 lb.-ft. @ 3700 rpm) |
| Engine layout | Rear, Transverse |
| Engine Model/Code | B38K15T0 |
| Engine displacement | 1499 cm3 (91.47 cu. in.) |
| Number of cylinders | 3 |
| Engine configuration | Inline |
| Cylinder Bore | 82 mm (3.23 in.) |
| Piston Stroke | 94.6 mm (3.72 in.) |
| Compression ratio | 9.5:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Direct injection |
| Engine aspiration | Twin-power turbo, Intercooler |
| Valvetrain | VALVETRONIC |
| Engine oil capacity | 4.25 l (4.49 US qt | 3.74 UK qt) |
| Kerb Weight | 1595 kg (3516.37 lbs.) |
| Max. weight | 1965 kg (4332.08 lbs.) |
| Max load | 370 kg (815.71 lbs.) |
| Trunk (boot) space – minimum | 88 l (3.11 cu. ft.) |
| Fuel tank capacity | 30 l (7.93 US gal | 6.6 UK gal) |
| Length | 4689 mm (184.61 in.) |
| Width | 1942 mm (76.46 in.) |
| Width including mirrors | 2218 mm (87.32 in.) |
| Height | 1291 mm (50.83 in.) |
| Wheelbase | 2800 mm (110.24 in.) |
| Front track | 1644 mm (64.72 in.) |
| Rear (Back) track | 1721 mm (67.76 in.) |
| Front overhang | 960 mm (37.8 in.) |
| Rear overhang | 929 mm (36.57 in.) |
| Ride height (ground clearance) | 117 mm (4.61 in.) |
| Drag coefficient (Cd) | 0.28 |
| Minimum turning circle (turning diameter) | 12.3 m (40.35 ft.) |
| Drivetrain Architecture | The Internal combustion engine (ICE) permanently drives the rear wheels of the vehicle, the electric motor drives the front wheels of the vehicle, capable of running in full electric mode, only by the Internal combustion engine (ICE) or in mixed mode. |
| Drive wheel | All wheel drive (4×4) |
| Number of gears and type of gearbox | 6 gears, automatic transmission |
| Front suspension | Double wishbone |
| 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 | Front wheel tires: 195/50 R20 Rear wheel tires: 215/45 R20 |
| Wheel rims size | Front wheel rims: 7J x 20 Rear wheel rims: 7.5J x 20 |
Powertrain & Engine Architecture
The i8 Roadster’s powertrain is a complex interplay between a 1.5-liter three-cylinder turbocharged gasoline engine (BMW’s B38K15T0 code) and a powerful electric motor. The engine, part of BMW’s modular engine family, utilizes direct injection and VALVETRONIC technology for precise control of valve timing and lift, optimizing both power and efficiency. The turbocharger, a twin-scroll unit, minimizes turbo lag and provides a broad torque curve. The electric motor, positioned at the front axle, delivers instant torque and contributes significantly to the car’s overall performance. The combined system output of 374 horsepower and 420 lb-ft of torque is channeled to all four wheels via a sophisticated xDrive all-wheel-drive system. The six-speed automatic transmission is specifically tuned to work seamlessly with the hybrid powertrain, providing smooth and efficient gear changes. The 11.6 kWh battery pack, located in the central tunnel, provides an all-electric range of approximately 33 miles (NEDC).
Driving Characteristics
The i8 Roadster’s driving experience is unique. In electric-only mode, it offers near-silent and surprisingly brisk acceleration, ideal for city driving. Switching to Sport mode engages both the gasoline engine and electric motor, unleashing the full 374 horsepower. While not a traditional sports car in terms of raw power, the i8 Roadster delivers a responsive and engaging driving experience. The instant torque from the electric motor fills in any gaps in the three-cylinder engine’s power delivery. The all-wheel-drive system provides excellent traction, and the low center of gravity, thanks to the battery pack’s placement, contributes to confident handling. Compared to the i8 Coupe, the Roadster offers a more visceral experience due to the open-top configuration, but it also carries a slight weight penalty.
Equipment & Trim Levels
The i8 Roadster came relatively well-equipped as standard. Interior features included leather upholstery, a premium sound system, and BMW’s iDrive infotainment system with a touchscreen display. Standard safety features included automatic emergency braking, lane departure warning, and parking sensors. Optional extras included upgraded leather options, a head-up display, and a more powerful Harman Kardon sound system. The Roadster’s interior design was modern and minimalist, reflecting the car’s futuristic aesthetic. The soft-top roof was fully automatic and could be raised or lowered in approximately 16 seconds, even while driving at speeds up to 30 mph.
Chassis & Braking
The i8 Roadster utilizes a lightweight chassis constructed from carbon fiber reinforced plastic (CFRP) and aluminum. This construction contributes to the car’s relatively low weight of around 3,500 pounds. The suspension consists of a double-wishbone setup at the front and an independent multi-link setup at the rear, providing a comfortable yet controlled ride. Brakes are ventilated discs all around, offering strong stopping power. The steering is electrically assisted, providing precise and responsive feedback.
Market Reception & Comparison
The BMW i8 Roadster received generally positive reviews from automotive critics. It was praised for its innovative technology, striking design, and engaging driving experience. However, some critics noted the relatively small trunk space and the limited all-electric range. Compared to other hybrid sports cars, the i8 Roadster stood out for its distinctive styling and its focus on driving dynamics. Against traditional gasoline-powered sports cars, it offered a compelling alternative for those seeking a more environmentally friendly option without sacrificing performance. Fuel economy was a strong point, with the i8 Roadster achieving impressive MPG figures in hybrid mode.
Legacy
The BMW i8 Roadster, along with the Coupe, represents a significant milestone in BMW’s history. It demonstrated the company’s commitment to electric mobility and showcased its ability to create a compelling and technologically advanced sports car. While production was limited, the i8 Roadster has become a sought-after vehicle in the used car market. The powertrain, while complex, has proven to be relatively reliable, with few widespread issues reported. The i8 Roadster’s innovative design and forward-thinking technology continue to inspire automotive enthusiasts and influence the development of future electric vehicles.
