BMW Z5 takes shape

BMW has confirmed the replacement for its six-year-old Z4 has been signed off and is now in concept stage, but it could still be a year away from showrooms.

Last week BMW told Bloomberg in a statement that a technical feasibility study for its sports car joint-venture with Toyota, which is expected to produce both a successor for the Z4 and a born-again Supra, has been successfully completed.

Further, the German car-maker said that co-operation on the underpinnings of both mid-size sports car “has moved on to the concept phase and is running according to plan".

However, our European sources have confirmed the new BMW sports car, which could be called the Z5, will not appear at the Detroit motor show in January and may or may not make its world debut at Geneva in March.

Either way, it's unlikely to reach Australia until late next year or perhaps even early 2016 -- almost seven years after the second-generation E89 Z4 was introduced here (in May 2009).

Toyota and BMW announced their intention to share technologies as early as December 2011, starting with diesel engines and then EV batteries in 2012, then the joint-venture sports car in June of that year. The pair began a technical feasibility study for their first co-developed model in January last year.

Both mid-size two-door two-seat sportsters — the highest-profile products in a partnership that will extend until at least 2020 — will share the same chassis architecture, wrapped in different bodies and motivated by different powertrains with shared hybrid technology.

Toyota has revealed a concept version of what its all-new model could look like in the form of the FT-1 concept, although some reports insist the Japanese giant's version will emerge as a Lexus – perhaps a production version of the LF-LC concept car.

Whatever badge it wears, the all-new Japanese sports car is due to emerge in early 2016 exclusively with a hybrid powertrain.

For BMW's part, the Z5 (rendered here by Automedia) will emerge first with conventional six-cylinder power, in the form of a new direct-injection 3.0-litre turbo-petrol inline six.

Codenamed B58, the new engine will debut in next year's new 7 Series, in which it will produce 250kW and 440Nm – which should be sufficient in a sports car expected to weigh less than 1400kg.

After that, the as-yet-unnamed BMW will become the world's first production car to use the rapid-discharge supercapacitors, developed by Panasonic for Toyota's Le Mans outright title bid.

While turbo-four engines will be offered at the bottom of the Z5 range, both sports cars will combine either a three- or four-cylinder turbo-petrol engine up front with a pair of electric motors driving the front wheels, resulting in what will be called 'Performance Hybrid all-wheel drive'.

Despite the performance focus, the sports car twins will be plug-in hybrids with the ability to drive on pure-electric power.

Apart from being lighter and easier to package than even the most effective lithium-ion batteries, the supercapacitors can also be charged more quickly and are able to discharge energy at a much faster rate.

While Toyota will handle the electronics work and body construction, BMW will develop the engine, produce the Toyota-designed electric motors and supply carbon-fibre know-how from its i-car program.

However, because European demand for convertibles has halved since 2008, BMW is expected to ditch the Z4's weighty folding hard-top and both models are likely to emerge only as coupes.