The BMW 2, 4, 6 and Z4 series vehicles, including each series M package, are all available in convertible models with a retractable hardtop, as of 2015. BMW retractable hardtops can automatically retract into the trunk and close during operation.
The 2 series is the least-expensive convertible BMW model, with most vehicles available for under $40,000. The vehicles are powered by a 2.0-liter BMW TwinPower Turbo inline four-cylinder engine with an eight-speed automatic transmission. The convertible option skips the 3 series and resumes with the 4 series. It has pass-through back seats that can fold down to store longer items from the trunk, even with the roof retracted. The roof can retract at driving speeds up to 11 miles per hour.
The 640 and 650 are the largest of the BMW convertible models available and have 3.0-liter six-cylinder and 4.4-liter eight-cylinder engines respectively. The Z4 is a two-door, two-seat roadster designed for driving enthusiasts and has seven-speed dual clutch, six-speed manual or eight-speed Sport automatic transmission options. The Z4 roof can retract at driving speeds up to 25 miles per hour.
The high-performance M class is available in the 2, 4 or 6 series vehicles. Suspensions, braking systems and engines in the M class are all enhanced for high speeds. M models are also significantly more expensive than their counterparts.