Alfa Romeo will finally launch a replacement for the iconic Spider in 2015, after Fiat Auto signed a provisional deal last week to base the car on the next-generation Mazda MX-5.

According to outline plans, Mazda and Alfa will develop two “differentiated, distinctly styled, iconic and brand-specific lightweight roadsters, featuring rear-wheel drive”. The two models will also feature “proprietary engines, unique to each brand”. Both cars will be built at Mazda’s Hiroshima plant in Japan. 

Fiat CEO Sergio Marchionne used the announcement to counter persistent rumours that the Italian company would eventually dispose of the ailing Alfa Romeo brand. "The agreement demonstrates our commitment to Alfa Romeo and the determination to grow it into a truly global brand," he said. 

With the binding agreement on the deal not due until later this year and production of the Spider some three years away, there is very little firm information available about the likely shape of the new Alfa. 

However, the new car is likely to be light and, for range-topping versions at least, potentially very rapid, thanks to a new version of Alfa’s highly respected 1750cc turbocharged petrol engine, which is due for launch early next year. The new engine, which has an aluminium block, high-pressure fuel injection and a maximum output of 296bhp, is designed for both transverse and longitudinal mounting. It should make its debut in the 2014 Alfa 4C mid-engined baby supercar.

The two new roadsters will be based on Mazda’s radical new SkyActiv lightweight steel spaceframe technology, which already underpins the new CX-5. Mazda engineers will use the same know-how, but the platform will be designed from scratch because it is both rear-wheel drive and particularly compact. 

However, because the MX-5 is two years from being introduced, it means that Alfa engineers can get involved at an early stage with the design and engineering of the new platform. This opens the way for the two roadsters to be pitched at different markets. 

Mazda sources say the company wants to take the next MX-5 back to its 1989 roots by making the new model more compact, less plush and lighter, bringing the weight down to under 1000kg in base-engined form.

Alfa Romeo, by contrast, will probably want to pitch its relaunch model upmarket, which might demand its version be more visually imposing than the Mazda. A wider track, more voluptuous styling and a plusher interior are likely for the new Spider. There’s no news on the look of the car, although any new Spider aimed at the North American market will have to make reference to the classic ‘boat tail’ Spider immortalised in the film The Graduate. 

It seems likely that this will not be the only co-operative project between the two makers. “We are appreciative for this collaboration with Mazda and look forward to maintaining a fruitful and continuous relationship,” said Marchionne. Mazda, meanwhile, said that establishing technology and product alliances is one of its corporate objectives.  

Loss-making Mazda, which has been hit by the strength of the yen, has been struggling to finance its future product development programme and its desire to build a new factory in Mexico. In February this year it raised £1.2 billion through a share issue. Forming alliances and sharing its SkyActiv engine and platform technology is widely regarded as an urgent necessity for such a relatively small company.