BMW i8 Roadster: silent running
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BMW has revealed a roadster version of its i8 sports car, which the company says is the world’s best-selling plug-in hybrid sports car.
The open-top two-seater with an electrically operated soft-top joins the updated version of the 2+2 seater version of the i8 Coupe, and is likely to arrive here next year.
“It opens the door to virtually silent motoring with zero CO2 emissions, bringing an extra edge of purity to the experience of open-top,” says BMW.
Like the new BMW i8 Coupe, the new BMW i8 Roadster is based on the LifeDrive vehicle architecture with an aluminium chassis and carbon-fibre- reinforced plastic (CFRP) passenger cell.
The BMW eDrive technology employed in both models includes a high-voltage battery with expanded cell capacity and energy content, and an electric motor generating a higher peak output.
When opened, the BMW i8 Roadster’s broad roof retracts fully into the rear end, creating about 100 litres of additional storage space behind the seats.
The company says the electric roof opens and closes quietly, in 15 seconds, and can be done while travelling at up to 50km/h. Dropping the roof raises the rear window 30mm to serve as a draught stop.
The roadster has frameless gullwing doors with additional struts and panels in the front and rear axles to help rigidity. Even so, BMW says the open-top model is only 60kg heavier than the coupe.
An updated version of the lithium-ion battery developed for the BMW i8 improves the cell capacity from 20 to 34ah, and gross energy capacity increases from 7.1 to 11.6kW. The cell configuration allows a 9kW increase in peak output to 105kW.
In the standard driving mode, the new models can be driven exclusively on the electric motor, — from zero to 105km/h, which is up from the original i8’s 70km/h. The combustion engine is brought into play only at higher speeds or when the driver stamps down hard on the accelerator, and is switched off again more frequently when a measured driving style is maintained.
Pressing the eDrive button allows both models to travel at up to 120km/h on electric power alone. The electric range of the new BMW i8 Coupe has increased to 55km, and the Roadster 53km.
BMW says the performance of the 1.5 litre engine has also been improved. The three-cylinder unit extracts maximum output of 170kW, with peak torque of 320Nm.
In the process, the company says it generates an even sportier soundtrack, and a filter is fitted to further reduce emissions by absorbing the particulate matter in the exhaust gases.
The output produced by the electric motor and engine in unison is now 275kW, and the coupe can accelerate from 0 to 100km/h in 4.4 secondsand the roadster takes 4.6 seconds.
Both models have an electronically limited top speed of 250km/h. Combined fuel consumption, as calculated in the EU test cycle for plug-in hybrid vehicles, stands at 1.9 litres per 100km for the coupe and 2.1 litres per 100km for the roadster, plus 14.0kWh and 14.5kWh of electrical energy respectively per 100km.
The electric motor’s power is transmitted to the front wheels and the engine’s drive to the rear, resulting in a hybrid-specific all-wheel-drive system controlled by the car’s intelligent energy management.
In hybrid mode, the electric motor boosts power boost to assist the engine when the driver is accelerating with vigour.
The petrol engine’s high-voltage starter-generator can likewise provide additional reserves so power is always on tap.
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