the Q4 e-tron and Q8 e-tron. Concept vehicles e-tron Frankfurt (2009) The first e-tron concept car was shown at the 2009 International Motor Show Germany. A two-seater, similar in appearance to the Audi R8 but slightly smaller, is powered by four UQM Technologies motors, providing four-wheel drive. Together, these produce and of torque, allowing the car to accelerate from 0 to in 4.8 seconds. A 42.4 kWh lithium-ion battery is located in front of the rear axle and provides a range of approximately with a full charge taking 6–8 hours from a normal household socket. It has ceramic disc brakes as well as regenerative braking. In 2010 Audi began a development program with the objective to manufacture a limited production R8 e-tron. The R8 e-tron made a brief appearance in the 2013 Marvel Studios release of Iron Man 3. After developing 10 prototypes for research and development purposes, in May 2013 Audi decided to cancel production of the electric car due to its limited all-electric range as battery technology had not advanced as quickly as Audi had expected, making the R8 e-tron unviable for series production. In March 2014 Audi revised its decision and announced it will build the R8 e-tron upon request. The carmaker explained that their latest development work resulted in an increased range from to approximately . e-tron Detroit showcar (2010) The Audi e-tron Detroit showcar (confusingly, also named "e-tron") includes 2 electric motors driving the rear wheels with a combined output of and of torque, with lithium-ion batteries behind passenger compartment and ahead of the rear axle, adaptive matrix beam LED headlight modules with clear glass covers, fully automatic light assistance system, Audi Space Frame with doors, lids, sidewalls and roof made of a fiber-reinforced plastic; built-in central display with integrated MMI functions, front axle hydraulic fixed-caliper brake, electrically actuated floating-caliper brakes mounted on the rear axle, heat pump, triangular double wishbones made of forged aluminum components at the front and rear axles, direct rack-and-pinion steering, 19-inch wheels of 35-spoke design, 235/35 front and 255/35 rear tires. The concept car can accelerate from in 5.9 seconds. The vehicle was unveiled in the 2010 North American International Auto Show in Detroit. A similar production model, based on a future mid-engined automotive platform codenamed 9X1, shared with Porsche and Volkswagen, is reportedly under development. A1 e-tron (2010) The Audi A1 e-tron concept car, an electric variant of the