While not much is known about the replacement for the BMW Z4, its mooted successor has been spotted undergoing winter testing in the snow.

The BMW Z5 Roadster is believed to be a collaboration between BMW and Toyota, and both car makers will be sharing this platform for an all-new mid-sized sportscar. BMW appearsfirst out of the gate with a prototype as Toyota's examplestill lurking in the depths of the brand's Research and Development centre.

From these photos we can see that it'll have a soft top, which will keep the weight down. Expect it to have typical Z4-like design cues such as a long bonnet and you can bet it'll have a mixed assortment of engines such as the rather good 2.0-litre turbocharged four cylinderseen in the Mini Cooper S JCW as well as the mighty 3.0-litre straight six turbo unit which is used in multiple applications. You can't rule out hybrid technology (as seen in the i8 hybrid sportscar)either.

If you look at BMW's Five Year plan here, it's safe to say that the earliest we'll get to see this vehicle in production trim will be 2018.