Just as the M3 Convertible was a 3 Series Convertible with the dial turned up to 11, the M4 is based off the 4 Series but boasts more under-hood might, a thoroughly reworked suspension and racier styling. It also packs a host of new technology features and lightweight materials.
In place of the M3 Convertible's characterful but thirsty 4.0-liter V8 is a downsized 3.0-liter inline-six that relies on twin turbochargers to produce 425 horsepower and 406 lb-ft of torque from just 1,850 rpm all the way to 5,500 rpm. Those figures represent gains of 11 ponies and, more importantly, 111 lb-ft of twist compared to the old eight, with peak torque arriving 2,050 rpm earlier.
Transmission options include a six-speed manual and a seven-speed dual-clutch automatic. The standard-equipment stick shift features a rev-matched downshift function and helps the coupe to accelerate from zero-to-60 mph in a claimed 4.4 seconds, while the seven-speed dual-clutch boasts launch control and a slightly quicker sprint time of 4.2 seconds. Also part of the septa-cog's bag of tricks is a "Stability Clutch Control" function that opens one of the clutches in order to quell understeer.
Fuel economy is rated at 17 mpg in the city and 26 mpg on the highway with the manual, while the dual-clutch is good for 17/24 mpg.
M compound brakes on all four corners and a stiffened, track-tuned suspension keep M4 Convertible's prodigious power in check. As expected, the M3 Convertible's hydraulic-assist steering gives way to a new, more efficient electric-assist setup with three different effort modes.
All M4s are equipped with an Active M Differential that keeps tabs on throttle inputs, the rotational speed of the wheels and the car's yaw rates in order to maximize traction.
Thanks in part to the increased use of carbon fiber reinforced plastic and aluminum in the body and suspension, the M4 is an impressive 90 lbs. lighter than the M3 Convertible. Contributing to the weight loss are components like the six-speed manual (-26 lbs.), smaller engine (-22 lbs.) and carbon fiber roof (-11 lbs.).
Looking the Part, Inside and Out
Outside, the M4 Convertible wears a heavily-sculpted front bumper, a discreet hood bulge and flared fenders all around. Air curtains mounted in the front apron team up with "Air Breathers" - that's BMW-speak for fender vents - to optimize airflow around the wheel arches and improve aerodynamics. Around back, a diffuser with inset quad tailpipes and a Gurney-style spoiler provide both style and function. Eighteen-inch rims are fitted as standard, while 19-inchers can be specified as an option.
The M4's cabin is closely modeled after the standard 4 Series, which means it includes a quartet of simple, driver-friendly analog gauges and a tablet-style 6.5-inch display screen mounted atop the dashboard that displays stereo and vehicle information. Shell out for the optional navigation system, and the screen is upgraded to a larger 8.8-inch unit.
All secondary systems are controlled through BMW's iDrive infotainment setup, which has evolved over the years from a bewildering complex unit to surprisingly simple and user-friendly system. Redundant controls on the steering wheel and dashboard provide alternate means of accessing the electronics.
Setting the M4 Convertible part from the standard 4 Series drop-top is an M-specific instrument cluster, a sporty three-spoke multi-function steering wheel, sports seats and carbon fiber trim on the dashboard and on the center console. Naturally, liberal helpings of M badging are also part of the package.
The M4 Convertible feature a fully power-operated retractable hardtop that can be lowered in roughly 20 seconds. Cargo space measures 13 cubic feet with the top up, and 7.8 cubes when the two-door is in sun-worshiping mode.
Standard and Optional Features
The M4 Convertible is fitted as standard with leather upholstery, heated and power-adjustable M front sport seats, a navigation system with 20GB of audio storage, an adaptive M suspension, rain-sensing windshield wipers, adaptive Xenon headlights, heated and power-adjustable exterior mirrors, a Homelink universal garage door opener, an AM/FM/CD stereo with HD radio, Bluetooth connectivity with audio streaming, AUX and USB ports and 18-inch alloy wheels.
Notable options include a head-up display, a front collision warning system, full LED headlights, and, on the performance end, lightweight and extra fade-resistant carbon ceramic brakes.
Buyers who want to hit the track can order an optional Competition Package. It includes a revised differential and a re-tuned Dynamic Stability Control (DSC) system.
BMW made a few modifications to the M4's turbocharged 3.0-liter straight-six engine. The six-banger now generates 444 horsepower -- 19 more than the stock model -- at 7,000 rpm and 406 lb-ft. of torque from 1,850 to 5,500 rpm.
Visually, cars equipped with the Competition Package stand out thanks to high-gloss Shadow Line trim designed by BMW Individual, 20-inch alloy wheels with M-shaped spokes, and a sport exhaust system with black chrome tail pipes.
All M4 Convertibles come standard with dual front, front side and front knee airbags, in addition to traction and stability control systems.
Lane departure warning, frontal collision warning and active blind spot detection can be spec'd as part of the Driver Assistance Plus package.
The M4 Convertible's closest rival is the Mercedes-AMG C63 S Cabriolet, which packs over 500 horses of V8 power. Buyers willing to trade some refinement in favor of higher performance can also consider the Chevrolet Corvette Stingray Convertible.