Mercedes-Benz is poised  to preview the all-new Smart Fortwo and Forfour with a pair of concepts at the Frankfurt motor show in September.

The third-generation Fortwo city car (codenamed C453) and the second-generation Forfour four-seat hatchback (W453) are both set to go into production next year. The Smarts are built around a new rear engine/rear-wheel drive structure, developed with partner Renault-Nissan.

The platform will also provide the basis for the third-generation Renault Twingo, which was recently previewed by the Twin’Z and Twin’Run concepts and is due next year.

The new platform is also claimed to be flexible enough to support varying wheelbases and track widths, providing the scope for models spanning both the city car and compact hatchback ranks.

Power for the two-seat Fortwo, which will once again come in both fixed-roof coupé and fabric-roof cabriolet body styles, will derive from a newly developed 900cc, three-cylinder petrol engine.

The Mercedes-Renault direct-injection unit will be offered in 65bhp naturally aspirated form as well as 85bhp and 105bhp turbocharged guises, in combination with a standard six-speed manual gearbox. A diesel won’t be available, but a seven-speed dual-clutch auto — sure to be superior to today’s automated manual ’box — will be optional.

There will also be a Fortwo e-drive with an updated drivetrain that includes a 90bhp electric motor and lithium ion battery pack.

The new Forfour — expected to be similar in style to the Forstars concept — is based on a stretched version of the Fortwo’s platform. It has a wheelbase of 2470mm and is twinned with the Twingo.

Conceived to provide space for four adults, it extends 820mm beyond the length of the new Fortwo (at 3550mm) and stands 1701mm high. 

Among the engine options for the Forfour will be the more powerful versions of the Fortwo’s turbocharged 900cc triple.