As BMW ramps up co-development of the next-generation BMW Z4 with Toyota, BMW's local boss wants to assure purists that the final Z4 product won't be anything like its Japanese counterpart.

Speaking to CarAdvice at the recent 1 and 2 Series LCI launch, BMW Group Australia CEO Marc Werner said the new Z4 will still be "an ultimate driving machine".

The Toyota tie-up, no surprise, is to take advantage of the cost benefits that come with sharing investment and combining resources.

"It's definitely economies of scale [the reason for this collaboration]," Werner said.

"Product development of each and every car costs you a couple of billion dollars, and the roadster segment is unfortunately declining over the last couple of years — not only for us [BMW], but each and every manufacturer.