At 4670mm in length, 1870mm in width and 1386mm in height, the new car is 56mm longer, 65mm wider and a scant 4mm lower than its predecessor. It also rides on a larger chassis whose 2812mm wheelbase and 1579mm front and 1693mm rear tracks are up by respective 52mm, 39mm and 63mm.
The three-piece metal roof opens automatically at the press of a button, taking 20sec to fold and stow behind the rear seats at speeds up to 11mph. Nominal boot capacity is put at 370 litres with the roof in place and 220 litres with it folded down – figures which represent a respective 20 litre and 10 litre increase on the M3 cabriolet.
Inside, M-specific upgrades include heated sports seats, an M steering wheel, and new chrome trim. In the UK, additional specification will include BMW's Professional media package, upgraded Bluetooth and USB functionality, front and rear parking sensors and folding mirrors.
Power for BMW M division’s latest open top comes from the same turbocharged 3.0-litre in-line six-cylinder engine already confirmed for the upcoming M3 saloon and M4 coupe. The direct injection petrol, assembled at BMW’s specialty engine plant located in Munich, unit kicks out 425bhp and 406lb ft of torque.
This is an 11bhp and 111lb ft increase on the naturally aspirated 4.0-litre V8 engine used by the old M3 cabriolet. Its keenest rival, the Audi RS5 cabriolet, continues to run a naturally aspirated 4.2-litre V8 with 444bhp and 318lb ft.
Channeling the new six-cylinder engine’s reserves to the rear wheels is a newly developed six-speed manual gearbox or optional seven dual clutch auto gearbox, a £2645 option.
At 1750kg in standard six-speed manual guise, the M4 cabriolet tips the scales 60kg below its predecessor, endowing it with a power-to-weight ratio of 243bhp per tonne. Official performance figures put its 0-62mph time at 4.6sec in manual form – 0.6sec faster than the M3 cabriolet and 0.3sec inside the time quoted for the 1920kg RS5 cabriolet.
The optional seven-speed dual clutch auto gearbox shaves a further 0.2sec off the benchmark sprint, lowering it to 4.4sec, 0.7sec faster than the similarly specified M3 cabriolet. Top speed continues to be limited to 155mph, while combined cycle consumption has improved by 7.8mpg in manual guise to 31.0mpg to provide the latest M car with average CO2 emissions of 213g/km. Those figures drop to 203g/km and 32.5mpg with the seven-speed DCT.
BMW says it has tuned the M4 convertible's suspension set-up for maximum precision, response and fuel efficiency. The car features a double-strut arrangement at the front, with an aluminium five-link set-up at the rear. Drivers can select from Comfort, Sport and Sport+ driving modes as part of the Adaptive M suspension package.