The little Smart cars built and sold by Mercedes have been an underwhelming seller for the German automaker, costing far more in production costs than expected and posting poor sales. Mercedes has lost about $4.6 billion on the cars, or around $6100 per car. In 2008 the small cars sold over 24,000 units but sales dropped as low as around 5,300 units in 2011. Mercedes is planning on building a new larger model in 2015 based off the small city car, the Renault Twingo platform. In real world terms, Renault Twingo users have reported mpg that ranges from 22mpg to nearly 69mpg. At 141 inches long, the Twingo is longer than the 106 inch long second generation Smart cars. The bigger frame will allow Smart to add a back seat or even four doors, making the car more practical for many customers.