The expansion of BMW's i sub-brand is inevitable, and the next obvious model in the pipeline is a sedan, likely wearing an i5 or i7 badge. But despite calling BMW's new electrically motivated sedan a "Tesla fighter", Car reports that it's going to use an internal combustion engine to extend range.

That's not entirely surprising given what BMW has done with the i8 by combining a turbocharged three-cylinder with an electric motor. What is surprising is that BMW will use its new modular architecture that's set to underpin the next 5 Series.

In it's "scoop dossier" on the next i, Car says that the sedan will use BMW's "Cluster Architecture" or CLAR, that breaks the chassis into interlocking pieces to shrink or expand it based on the application. For the i5/i7, BMW is opting for the next 5er's long-wheelbase variant to house the batteries in a similar "backbone" as the i8 (and Chevy Volt), extending from front to rear.

Unlike the i8, however, two electric motors will power the sedan, with one sending 204 HP to the front wheels and another, smaller unit, sending 95 HP to the rear. That will be combined with a turbocharged four-cylinder putting out 245 HP, allowing the sedan to run in three modes: electric front-wheel drive, electric rear-wheel drive, and blending the engine and motors for all-wheel drive.

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Car says that the battery – of unknown size – will be capable of hauling the i5/i7 for 80 miles on electric power alone, but as soon as the speed gets above 40 MPH, the engine would kick in.

With the next 5 Series due out in the in two years, BMW is reportedly planning to launch its range-extending EV in 2018. Car pegs the pricing "from just below the Tesla to more than $125,000", which is a pretty massive spread, but rightly points out that it's just in time for the new CARB rules that require 4.5 percent of vehicles sold in California to be zero emission vehicles.