BMW has released the latest version of their successful BMW i8 series which is the BMW i8 Roadster. The open-top two-seater utilises electrical soft-top caters to a whole new market who want open top cars. Like the new BMW i8 Coupe, the new BMW i8 Roadster is based on the LifeDrive vehicle architecture with aluminium chassis and carbon-fibrereinforced plastic (CFRP) passenger cell.
BMW has further optimised their eDrive technology employed in both models which comprise of a high-voltage battery with significantly expanded cell capacity and energy content, and an electric motor generating a higher peak output. The result is a noticeable increase in dynamic performance, operating range and the amount of driving possible using purely the electric drive system.
When opened, the BMW i8 Roadster’s broad roof retracts fully into the rear end. A unique mechanism allows the soft-top to be folded into a compact package and stowed away in a perpendicular position, creating around 100 litres of additional storage space behind the seats. The all-electric roof opens and closes very quietly in 15 seconds, a process which can be initiated while travelling at up to 50 km/h. Dropping down the roof raises the rear window by around 30 millimetres into a comfort position, where it can serve as a draught stop.
The familiar lightweight design measures used for previous BMW i models have been meticulously adapted to the specific requirements of the i8 Roadster. The open-top two-seater comes with newly designed frameless gullwing doors made from CFRP with an aluminium outer shell, while the windscreen frame is made entirely from CFRP. This ultra-strong high-tech material is ideally equipped to provide exceptional rigidity, maximising the car’s occupant protection even if it rolls over.
CFRP is also used to manufacture the side skirts with their extra-large crosssection. Additional struts and panels in the front and rear axles also help to maximise the body’s rigidity. The unladen weight of the new BMW i8 Roadster stands at 1,595 kilograms, meaning the design’s inherent weight penalty vis-à-vis the Coupe is limited to around 60 kilograms, a remarkably low figure for an open-top car.
The high-voltage unit is located centrally in the car’s underbody. Its cell capacity is up from 20 to 34 Ah and gross energy capacity rises from 7.1 to 11.6 kWh (net: 9.4 kWh). All of which means the electric motor has more energy at its disposal. The cell configuration allows a 9 kW/12 hp increase in peak output to 105 kW/143 hp, lacing quick sprints on pure-electric power with an even more vivid streak of dynamism.
In the standard driving mode, the new BMW i8 Coupe and new BMW i8 Roadster can be driven exclusively on the electric motor alone – from step-off to a speed of 105 km/h, which is up from 70 km/h in the original i8. The combustion engine is only brought into play at higher speeds or when the driver stamps down hard on the accelerator, and is switched off again far more frequently when a measured driving style is maintained. Pressing the eDrive button allows both models to travel at up to 120 km/h on electric power alone. The electric range of the new BMW i8 Coupe in the NEDC test cycle has increased to 55 kilometres and the new BMW i8 Roadster posts a figure of 53 kilometres.
The internal combustion engine has also undergone further optimisation to ready it for the new BMW i8 Coupe and new BMW i8 Roadster. The three-cylinder unit extracts maximum output of 231 hp from its displacement of just 1.5 litres, along with peak torque of 320 Nm. In the process, it generates an even sportier soundtrack. A particulate filter is now fitted to further reduce emissions by absorbing the particulate matter contained in the exhaust gases.
The system output produced by the electric motor and engine acting in unison is now 374 hp. The new BMW i8 Coupe accelerates from 0 to 100 km/h in 4.4 seconds, while the new BMW i8 Roadster takes a tick longer with a time of 4.6 seconds. Both models have an electronically limited top speed of 250 km/h.
The model-specific tuning of the suspension and damping systems, the specially configured steering characteristics, a firmer roll stabilisation set-up and targeted modification of the DSC parameters together guarantee that the new BMW i8 Roadster retains all of the plug-in hybrid sports car’s trademark handling and performance qualities. Dynamic Damper Control is included as standard on both models. The standard 20-inch light-alloy wheels fitted to the new BMW i8 Roadster feature a lightweight construction and each weigh around one kilogram less than the lightest wheels previously offered for the BMW i8.
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