BMW M4 Convertible.. loses weight

Identified as a unique model since the name change from 3 Series to ‘4 Series’ for the coupé and convertible 3 Series, the F83 M4 Convertible replaces the E93 M3 Convertible and the good news is it’s a lot lighter than before.

The outgoing M3 tipped the scales at 1,810kg DIN when fitted with the standard 6-speed manual gearbox, while the new M4 Convertible lowers this to 1,750kg despite retaining a three-section folding metal roof.

Strangely though, choosing the optional seven-speed M Double Clutch Transmission adds an extra 40kg to the M4 Convertible’s kerb weight rather than the 20kg penalty of its M3 predecessor.

By comparison the M3 Saloon weighs 1,520kg DIN while the M4 Coupé a class-leading 1,495kg. For obvious reasons, unlike the saloon and coupé, the M4 Convertible lacks their carbon roof, which saves around 7kg over an equivalent metal roof.

Powering the M4 Convertible is BMW’s newly developed M TwinPower turbo six-cylinder engine already fitted to the M3 Saloon and M4 Coupé. Power remains at 425bhp with 550Nm (406 lb-ft) of torque spread across a wide rev range.

Acceleration remains close to the saloon and coupé with a 0 – 62mph time of 4.4 seconds when fitted with the optional seven-speed M DCT gearbox (compared with 4.1 seconds). With the standard 6-speed manual transmission that time drops to 4.6 seconds. Official fuel economy figures show the M4 Convertible can be whisked along while consuming just 32.5 mpg and emitting 203 g/km of CO2.

Like the saloon and coupé, the M4 convertible adheres to the same lightweight construction principles, with aluminium used for the bonnet, front side panels and many of the components in its chassis.

While it may forego a lightweight roof, carbon-fibre-reinforced plastic (CFRP) is used in its single-piece driveshaft and for the beautiful suspension strut within its engine bay. Weighing just 1.5kg, this contributes to the M4 Convertible’s improved steering response and precision and the 60kg weight loss compared to its predecessor.

BMW have made great strides in improving the hard-top roof’s sound insulation, thanks to a “noise-absorbing” headliner, which reduces wind noise by up to 2 dB. As before the roof can be opened and closed in just over 20 seconds, while it can be lowered at speeds of up to 11 mph.

One of the main benefits of an open-top M car is the increased exposure to its aural delights – BMW have fitted an electrically-controlled flap in the twin-pipe exhaust system which reduces back-pressure, increasing the unmistakable sound entering the cabin from its inline six.

As with the saloon and coupé, the M4 Convertible features an electronically controlled multi-plate limited-slip differential to minimise slip and maximise the fun to be had when it slides. The unit works together with the DSC (Dynamic Stability Control) system, enabling between 0 and 100 per cent of lock on the rear axle, thus optimising traction in response to the position of the accelerator pedal, the rotational speed of the wheels and the car’s yaw rate.

The M4 Convertible is fitted as standard with BMW M compound brakes, answering criticism in the previous four generations to the easy-fade nature of their sliding-caliper units. The new brakes are claimed to provide outstanding stopping power and a high resistance to fade, as well as being much lighter than before. For customers with a penchant for track days, BMW offer an optional upgrade to M carbon ceramic brakes which are easily spotted by their signature gold-painted callipers.

The new M4 Convertible goes on sale on 6th September priced from £60,730. Standard equipment in the UK includes the 19-inch M light alloy wheels, BMW Professional media package, upgraded Bluetooth and USB, front and rear Park Distance Control, Folding exterior mirrors and heated front seats.

The BMW M4 Convertible will make its world debut at the 2014 New York International Auto Show on April 16 along with the new X4.