BMW M4 Convertible 2014 Review

An impressive 250kg of mass found its way onto the new BMW M4 Convertible as it morphed its way from the storming BMW M4 Coupe and it’s now a 1750kg proposition.

That’s no real surprise because it’s the sort of thing that almost always happens with a four-seat convertible, but it’s just about all you need to know if you want to know whether the M4 Convertible is a stormer, like its Coupe brother. It isn’t.

And yet it still manages to be a pretty good car, if you like that sort of thing. Historically, about 15,000 people per generation do, which isn’t a lot when you consider that’s a global figure stretched over a full life cycle. You can figure on it actually being about 2000 to 3000 cars a year and it’s a number that’s been fairly static since the first one showed up in Germany in 1988.

This one is a curious amalgam of M4 Coupe and the reinforcement engineering found beneath the standard 4 Series Convertible.

On one hand, there’s that wonderfully strong 317kW straight six, complete with two turbochargers and more torque than the Audi R8 V10. Yep, it twists out 550Nm of torque from just 1850rpm and it stays there, giving the gearbox curry, until 5500rpm.

Not coincidentally, that 5500rpm point-of-fade for the torque curve is precisely the same point in the rev range where the power peaks, though it stays up at the 317kW plateau until 7300rpm and the engine hits its limiter just 300 revs further around the tacho.

It’s a strong motor, then, and BMW mates it to either a standard six-speed gearbox (that’s a very unlikely starter in Australia) or a seven-speed dual-clutch transmission, which makes the car both faster and more economical.

A dyed-in-the-wool rear driver, the Convertible gets exactly the same trick active limited-slip differential and variable electromechanical rack-and-pinion steering system as the Coupe. It has the same suspension architecture, too, although it’s adjusted for the car’s increased mass.

The Convertible is larger than the M3 version it replaces, but that mass jump has come about largely because of the reinforcing beneath the floor rather than the three-piece folding metal roof above it.

The 435i Convertible is only 215kg heavier than the equivalent Coupe, yet the M4 Convertible adds 250kg and M can only propose it’s because the extra performance demanded extra reinforcement under the body. Some of it is built in, some of it is bolt on, but it all adds up.

And, from what we found, it doesn’t always add up to match the delivery of the powertrain, with scuttle shake and a visibly wobbling windscreen surround arriving over mid corner bumps with perhaps two-tenths of the car’s ultimate grip level still to be explored.

That alone turns the M4 Convertible into a more relaxed cruiser than the Coupe, but combine it with the weight and you’ve got two convincing reasons to dial the three-step gearshift into its softest setting and just enjoy the engine and the sumptuous interior.

Do that and you’ll find the Convertible taking just 0.3 seconds longer than the Coupe to cover the sprint to 100km/h and it still stretches upwards to a 250km/h speed-limiter (we found the head-up display indicating 268km/h on the autobahn south of Munich, but not a scrap more).

It’s a limiter the car will crunch into whether the roof is up or down, indicating there’s plenty more speed where that came from, especially when the roof is up and fixed. Not only does it add more speed and acceleration at the upper reaches, but it goes a long way towards eliminating the body flex in firm cornering, too. And it’s whisper quiet when you’re cruising, but that’s hardly the point of the Convertible.

Going topless adds some more character to the S55B30 engine’s delivery, too, with the cabin being permeated by the whistling of the twin Honeywell turbos and some chatter on the overrun that you’ll never find with the roof welded in place.

It’s also louder, though losing the roof also seems to have lost some of the nuance and timbre change from the (artificially enhanced) vocal efforts of this engine in the Coupe and often what it delivers with more revs is simply the same notes, delivered louder. Fortunately, they’re impressive notes.

One possible hiccup you might find is that the fuel tank is just 60 litres, while the claimed NEDC economy number is 8.7L/100km, which can be doubled comfortably with any enthusiastic pedalling. Drive it as a proper M car and that extra weight will have you reaching for a bowser far quicker than those in the Coupe.

Be prepared if you want to fling the roof up or down on the move, though, because it can only be done at up to 18km/h (though that’s an impressive engineering feat with a roof this large) and it takes 20 seconds, and it feels like a very genuine 20 seconds, too.

When the roof is finally down, you probably should put up the wind blocker (if there’s nobody in the back seat) and BMW now offers a first for an M car – an optional neck warmer. Yes, this is what M is reduced to with the Convertible.

On the upside, it’s a genuine four-seat convertible, especially if those in the rear are kids, and the wind blocker makes chatting comfortable even at very high speeds. And, unlike most of the wind blockers around the place, this one folds into a small space and BMW has thoughtfully given it its own storage area behind the folding rear seats, just ahead of the generous through-loading portal.

The M4 carries over the 435i Convertible’s neat trick in the boot to help you load it (there’s 220 litres of space when the roof is folded away). A button on the inside of the boot lid lets you lift the metal roof pieces up and down and, while it looks like a glorified trash compactor, its actual benefits to loading seem dubious at best. Especially we’d much prefer the car had an automatic boot release.

The dual-clutch transmission can fit into this more relaxed style of M driving beautifully, thanks to its whisper-neat softest setting. It’s perhaps too firm for the car’s character in its sportiest setting and having three shift settings on a car like this seems like one too many. Still, it’s hard to fault the gearbox in any meaningful way.

The steering, too, seems overly filtering in its comfort setting and needs to be skipped through the Sport setting into Sport Plus before it feels like a real M4 steering set-up, delivering just enough road feedback to make the car feel like it’s as into the whole fast-driving thing as you are. Fortunately, you can separate the settings for the steering, damping and gearshift and set them all individually.

Yet while the car doesn’t lose much to the Coupe on the low-speed sprint, it feels considerably more relaxed above about 150km/h as the added mass begins to take its toll on the mighty mill. Just as it does on the rubber and the 18-inch alloys in cornering.

This entire test has been a little damning with faint praise, but that’s not quite fair, especially to the people who live for this sort of car. The trouble is it will always be measured against its Coupe brother and it will fall short.

And it should (but usually won’t) be measured against the 435i Convertible which, with an M suspension pack on it, gets close enough on most measures to make the utterly rational reconsider the extra spend to cross over to the M4.

But which M3 (and now M4) Convertible has ever been bought via an utterly rational decision process?