BMW's Z-series roadsters, (l-r) the Z1, Z3, Z8 and Z4
But these days, BMW isn't just in the business - it's one of the leading roadster builders in the world. So how did it get here? By starting at the beginning, with the 315/1, a hopped-up, topless version of the 315 Saloon, first built in 1934.
Dubbed a Sports Roadster, the 315/1 featured just two sport seats, a raked windshield and a roof intended only for emergencies. Technologically, the car now seems archaic, but at the time it was pushing the limits of what could be done.
A 1.5L six-cylinder engine turned out a whopping 35hp (26kW) in the 315 sedan, but BMW tuned that up to 40hp (30kW) for the roadster. The engine featured a one-piece crankcase and cylinder block, a single cam with rocker arms actuating tappets to control the valves.
All of that technology is gone these days, though the inline six-cylinder configuration remains.
Performance was fitting, with top speed reached at 75mph (120km/h). In its day, that was enough to make a top contender, however, with the motorsport version of the car taking victory at the 1934 Alpine Rally.
One of the most impressive of the cars ever built was a 315/1 Special, built by BMW works driver Ralph Roese. It featured a significantly re-worked version of the engine that generated a huge 136hp (101kW) in a body that weighed just 838lb (380kg).
The evolution of the modern Z-series roadsters has been a long and winding road, from the Z1 in the late '80s and early '90s, to the ubiquitous Z3, the limited-run Z8 and today's Z4, eventually reaching a level of competence and style that is almost universally applauded.
For more on the current Z4 and its features, check out our coverage here.