The CS uses the lightweight carbonfibre-reinforced plastic bonnet and rear diffuser of the GTS and adds its own new fixed-height front splitter and rear gurney spoiler both made out of the same stuff, keeping the carbon roof of the regular M4 Coupe. Inside it’s got the weight-saving lightweight door skins and centre console of the GTS as well as the special pared-down stereo. But it’s also got back seats.
Unlike the GTS it doesn’t get lightweight carbon buckets up front or BMW M’s carbon-ceramic brakes as standard. Also, instead of the GTS’ mind-bogglingly complicated coilover suspension, the CS uses a retuned version of the M4 Competition’s suspension fitted out with new forged wheels and Michelin Pilot Sport Cup 2 tyres.
The upshot is that the new M4 CS goes only some of the way towards matching the weight saving of the GTS. It’s 35kg lighter than an M4 Competition (before you add those optional carbon stoppers) while the GTS enjoyed about twice that advantage.
But that’s only half the picture. The M4 CS’ engine makes a sizeable improvement to the real-world performance of the even the M4 Competition mostly by matching the peak torque of the GTS – 442lb ft – without the need for that water injection system. Amazingly, the engine’s internals are the same as those of the Competition Package car but its software management is new and simply works its twin monoscroll turbos harder at middling revs.
Peak power increases to 454bhp, which remains a distance behind what the likes of the Mercedes-AMG C63 S Coupe and Alfa Romeo Giulia Quadrifoglio saloon make. But BMW M will be trusting CS owners to realise that the combination of 10 per cent more torque, 35kg less weight and some additional Cup-tyre-derived traction delivers this new M4 a 0-62mph claim of under four seconds: 3.9- to be exact. Which is just a tenth off that of an M4 GTS, and exactly what’s claimed for both the Mercedes-AMG and the Alfa: another box ticked.
You install yourself into what seems like the same comfortable, thickly bolstered sports seat of the M4 Competition when you first get into the CS, identical but for an illuminated logo on the backrest, a change to the upholstery theme and manual rather than motorised adjustment. The lightweight door skins and centre console on either side of you immediately bring the GTS to mind, conjuring a pleasing extra layer of performance purpose for the cabin that the ‘alcantara’ suede trims for the fascia, transmission tunnel, roof and door consoles echo. The manual, single-zone climate control system, slightly thin-sounding but respectable hifi and ‘Professional Media’ infotainment system combine to strike just the right balance between a sense of apparent hardcore purpose and pragmatic real-world usability. This is a car you’d happily drive every day, that has the convenience features you want of a modern German performance machine, but that’s deliciously light on the luxury trimmings.
Stereo aside, it’s also much better to listen to than a ‘normal’ M4. The car’s quad exhaust system is the same as the one on the M4 Competition but, shorn of some sound deadening and with the CS’s new engine management in play (and a redline extended to 7600rpm) the CS sounds much more gritty and real than a standard M4. Not as angry as the titanium-piped GTS, granted; not even close. But the improvement in the appeal of the car’s sonic character is plain. And it helps no end that BMW M’s lightweight door skins remove the stereo system’s door speakers that might otherwise broadcast the ‘engine sound modulation’ so many object to in the normal M4. You still get some electronic augmentation of the engine sound but, at low and medium revs and under load, the perfectly synthesized digital warble of a normal M4 is replaced by a much more detailed, spikey and authentic engine rumble that you’ll instantly warm to on digging into the accelerator pedal travel.
BMW gave us a couple of hours only in its new car, on roads around the Nürburgring Nordschleife made busy by crowds gathered for the annual ‘N24’ endurance race. But even here, with no opportunity to really test the car up to the limit of its dynamic abilities, two things were clear: that the additional performance served up by the CS’s engine is probably even greater than BMW’s claims suggest, and that the extra grip and body control created by its chassis not only makes the CS a more composed and precise handling car than a normal M4, but also one very at home on the road.
As in any other M4, the CS allows you to select from ‘Comfort’, ‘Sport’ and ‘Sport+’ modes for its adaptive dampers, power steering and engine calibration; to choose between three shift modes on the standard seven-speed ‘M DCT’ twin-clutch gearbox; and between two dynamic stability control modes besides the obligatory ‘DSC off’ setting. Whichever mode you’re in, there’s a small but tangible improvement in contact patch feel through the car’s steering and a perceptibly sharper initial handling response as you feed the wheel through about 45 degrees either side of dead-centre.
I’d defy anyone who didn’t know as much to believe it after a drive in the CS, but the car’s extra steering feedback and body control come entirely from its new forged wheels and ‘cup’ tyres (the former an inch smaller in diameter up front, the latter getting a widened section at the rear, just like the GTS) and from redeveloped software calibrations for its dampers, power steering and active differential. There are no hardware changes to the M4 Competition’s springs, dampers or anti-roll bars here. And yet back-to-back testing against an M4 Competition revealed that the ‘CS’ turns in even more instantly and keeps its body more level during hard cornering, with better vertical body control and less float over really testing lumps and bumps, but without any greater harshness of ride, shortage of compliance or evidence of bump-steer.
The CS’s handling balance is similar to that of its sister car. Where the engine’s greater mid-range torque allows you to give the driven axle more to do as you unwind the steering and exit a bend, those cup tyres reply with even greater adhesion, stability and traction than a regular M4 has. The CS enters bends flat and fast, then, and exits them even quicker with a composure unknown to the Competition Package car. You’d never believe a set of rims and tyres and a new adaptive damper tune could achieve so much. I suspect both a Mercedes-AMG C63 S and an Alfa Romeo Giulia Quadrifoglio have more adjustable handling; but I also suspect neither would produce the same needle-threading sense of handling accuracy as the CS has, which is its own reward on the road.
And I’d be very interested to compare the torque curve of the CS’ 3.0-litre straight six to that of the M4 Competition because the new car feels much stronger through the middle of the rev range. This is probably where the M4 most needed attention, the standard car just beginning to feel a touch weedy compared to the very quickest of its rivals - at least until its motor starts spinning beyond 5000rpm.
But the CS doesn’t feel weedy. At all. That extra torque has a big impact on its in-gear pace between 3000- and 5000rpm, and there’s quite a lot more acceleration on tap where you really need it as you power away from corners and along slip roads.