The third-generation fortwo and second-generation forfour (see video here) have been developed in partnership with Renault alongside the new Twingo as part of the firms’ alliance and bring major changes as part of a ‘total rethink of urban mobility’.

‘The new smart fortwo and forfour adopt the proven concept while offering more of just about everything – more space, more colour, more equipment… and even more fun in the city! Only the vehicle length remains as unique as ever, at 2.69 metres,’ said smart boss Annette Winkler.

The two model share many styling cues, such as the headlamps, the cooling air grille in the front and the iconic tridion safety cell.

Smart also promises clever use of interior space. Additional highlights include the rear doors opening by almost 90° on the smart forfour and the folding front passenger seat backrest which comes as standard for all variants.

The changes see the hallmark smart rear engine concept now being offered for the first time in the four-seater smart forfour as well as the fortwo.

‘In the planning phase we were clear that we wanted to retain the rear engine for the new smart, so as to continue to exploit the vehicles' strengths to the full in the city,’ said Jörg Prigl, head of the product group Compact Cars at Mercedes-Benz. ‘On this basis, we then developed the new fortwo and forfour together with our partner, Renault.’

Both model use a completely revised chassis and newly developed suspension including a new front axle design based on the previous C-Class and de Dion rear suspension, bringing benefits including markedly improved ride quality and an unprecedented small turning circle – the fortwo boasts the smallest turning circle of any car.

‘Despite increased safety requirements, we have managed to retain the smart fortwo's unique length of just 2.69 metres,’ added Markus Riedel, head of development at smart. ‘It shares its architecture with the new forfour. We have tailored both of the vehicles to the needs of modern-day city traffic. My team is particularly proud of the turning circle, which sets a brand new benchmark at just 6.95 metres for the fortwo.’

Meanwhile the new smart forfour turns almost as compactly as the previous fortwo at 8.75m wall to wall.

The fortwo remains compact at 2,695mm in length with the wheelbase 8mm longer at 1873mm. It also boasts a 100mm wider track whilst height remains the same as before at 1,550mm.

The latest Forfour is 3,490mm, 255mm shorter than its original but offers improved boot space of 975 litres – the benchmark in its segment, whilst delivering a 2.22m loading length with the front passenger seat backrest folded forward.

The engine line-up comprises three-cylinder engines rated at 60PS, 71PS and 90PS, married up to a five-speed manual transmission or the twinamic automatic dual clutch transmission. No diesel will be offered but an electric drivertrain developed with Tesla is due in 2016, with the third-generation smart fortwo electric drive launched in 2012 available until then.

In Europe, three trim levels will be offered – passion, prime and proxy – said to bring kit normally seen in higher-segment vehicles. The entry-level versions of both models include LED daytime driving lights, central locking with radio remote control, control with variable speed limiter, instrument cluster with monochrome LCD display and trip computer and electric windows in the front.

Both models retain the tridion cell rigid shell architecture to bring advanced safety benefits whilst a high proportion of ultra-high strength hot-formed steels and maximum-strength multiphase steel is now used on the new smart. Meanwhile advanced assistance systems previously seen in higher classes vehicle are used and include Crosswind Assist (standard), forward collision warning (option) and Lane Keeping Assist (option).

The new smart generation will be launched onto the market in Europe in November. The price for the smart fortwo with 71PS engine will be under 11,000 euros, while the smart forfour will cost only around 600 euros more with the same engine.