The BMW Z5 will use conventional soft top.

BMW's next-generation Z roadster has been spotted undergoing shakedown testing on Germany's Nurburgring. BMW's new open-top sports car is expected to debut for the 2019 model year.The car seen here will replace BMW's previous Z4 roadster, but it remains unknown what the new car will be called. We've heard rumors that BMW will call it the Z5, but there have also been reports that the roadster will retain the Z4 name. For now, let's call it the Z5.

The Z5 will ride on an all-new rear-wheel drive platform co-developed with Toyota. Although Toyota helped with platform development, the Z5 is expected to come with BMW's own turbocharged four- and six-cylinder engines. However, BMW might eventually offer a Z5 model with a Toyota-sourced hybrid system.

Although the previous Z4, which went out of production about a year ago, used a retractable hardtop, this new Z5 will employ a conventional soft top. That should give the Z5 a bit more interior room, although it will remain strictly a two-seater.

We could see a concept car that previews the Z5 sometime this year, but a production version of the sports car isn't expected to debut until sometime in 2018. It'll probably be about a year before we see the Z5 in BMW showrooms.