Mercedes-Benz SL-Class vs BMW M440I

What's the difference?

The new Mercedes-AMG SL63 4Matic+ is guaranteed to turn heads for decades to come. But there’s enormous design and engineering substance underpinning this car’s undoubted good looks. Stunning performance, superb dynamics and top-shelf safety make this a powerhouse GT to be reckoned with.

Note: CarsGuide attended this event as a guest of the manufacturer, with accommodation and meals provided.

BMW has once again delivered a supremely enjoyable sports car with its new 2021 4 Series.

Sure, it might have love-it or hate-it styling, but those that dismiss the 4 Series based solely on looks are missing out on a wonderful driving experience.

With the base 420i offering all the style in a relatively affordable pricetag, while the all-wheel-drive grip of the M440i adds extra assurance at a more premium price, BMW's new 4 Series should cater to anyone looking for a premium sports coupe.

Rather than a strict two-seater, this time around the SL adds the flexibility of ‘+2’ rear seating while the previous 'Vario’ folding hardtop has been binned, the new car returning to a traditional, electrically-folding and weight-saving (-21kg) soft top. 

Mercedes-Benz design chief Gorden Wagener started the new model’s development from a ‘clean sheet’ and Mercedes-AMG says “not a single component comes from the predecessor SL, or any other model such as the AMG GT Roadsters”. 

Always a subjective call, but I think this car’s proportions are just about perfect. The lengthy bonnet with its twin longitudinal ‘Power Domes’, raked windscreen and fat haunches create a wide stance and presence that’s almost impossible to ignore.

Aggression, as with the sinister headlights and 21-inch rims, is subtly combined with soft curves along the flanks and around the rear. Note the seamless door handles.

And it’s not all about aesthetics. Active aero has been integrated into the front apron and retractable rear spoiler. Plus the ‘Z-fold’ roof design does away with the need for a separate cover.

The interior is sub-zero cool with slick screens, an 11.9-inch display covering multimedia and a 12.3-inch unit for instrumentation ahead of the driver, being particular highlights.

Turbine-style air-vents at the leading edge of the split-level dash and alloy trim elements are a tip-of-the-hat to SLs past and the deft mix of large flat surfaces with complex curves oozes design confidence.

Let’s get this out of the way. The 2021 BMW 4 Series is not an ugly car, despite what you may think from the press photos found online.

Is it to everyone’s tastes? Of course not, but I find the gaudy, in-your-face gold-on-black that is Versace’s signature styling a little gross … so your milage will definitely vary on the 4 Series like mine does with high-end fashion.

In person, that grille is nowhere near as overwhelming as pictures may have led you to believe, and blends in very nicely with the aggressive and muscular front end of the 4 Series.

In profile, the high shoulder line and slim glasshouse add to the sportiness, as does the sloping roofline and butch rear haunches.

The rear though, is arguably the 4 Series best exterior angle, as the pinched bumper, wraparound tail-lights, large exhaust outlets and subtle rear diffuser combine well for a properly sporty and premium look.

All Australian-spec cars come with the M Sport package, meaning a full bodykit, and 19-inch wheels to make even the boggo 420i look aggressive on the road.

Does it work? Well if it wasn’t wearing a BMW badge then it might not get away with this ostentatious styling, but being a big premium player, we think the 4 Series gets away with being as brash and in-your-face as it is.

We actually love that BMW has taken a risk with the 4 Series’ aesthetics and is willing to push the envelope because, after all, it could have just looked like the 3 Series sans-two doors, and that’s just a bit too safe, isn’t it?

Inside, the 4 Series is familiar BMW territory, which means a thick-rimmed steering wheel, glossy shifter and brushed metal accents, as well as high-quality materials throughout.

The dashboard-integrated multimedia system is a particularly nice touch, as are the metal accents that separate the lower and upper halves of the cabin.

So, is there anything interesting about the design? Absolutely. It’s got the internet talking more than usual and will no doubt draw the eye of those wanting to stand out from the often-samey crowd of German sports cars.

In the context of a high-performance GT, practicality is pretty impressive.

At just over 4.7m long the SL is a sizeable machine and much of its lengthy (2700mm) wheelbase is devoted to making the driver and front passenger comfortable.

There’s plenty of space for that pairing and just enough storage to cope with the ‘things’ they’ll typically bring with them.

Door pockets offer enough room for a few odds and ends, although you’ll struggle with even a medium-size bottle unless you’re willing to lay it down horizontally along the top of the aperture.

A handy lidded bin between the front seats doubles as a centre armrest, there are two cupholders under a sliding lid in the centre console and the glove box is a decent size. 

Power and connectivity options run to four USB-C ports, a 12-volt socket and the wireless device charging pad.

Then there are the rear ‘+2’ seats, and Mercedes makes no bones about the fact they’re intended for occasional use only, even suggesting a 1.5m occupant height limit.

And there’s no doubt they offer a handy emergency seat or a fun kids’ zone. Just ask a Porsche 911 Carrera owner how much this kind of seating arrangement increases a sports car’s flexibility.

At 183cm I gave the back seat a crack, which meant sliding the front (passenger) seat way forward with the backrest close to upright. But I squeezed in, and there was just enough legroom for a person in front at the same time. 

With the roof in place there’s the added pleasure of cranking your head over to around 45 degrees. But it’s do-able! 

No storage, adjustable ventilation, or power back there. But that’s fair enough, especially given there are USBs available in the front centre storage box.

Boot volume is 240 litres with the roof up and 213 litres with it folded, which is enough for some light luggage, and not too shabby when you think a Toyota Corolla hatch offers up just 217 litres (with all seats up).

There’s a 12V socket in there, but don’t bother looking for a spare, in the event of a flat your only option is a repair/inflator kit.

Measuring 4768mm long, 1842mm wide, 1383mm tall and with a 2851mm wheelbase, the 2021 BMW 4 Series certainly looks commanding on the road, and the generous proportions do well for interior space too.

Of note though, the M440i is slightly longer (4770mm), wider (1852mm) and taller (1393mm) than the 420i and 430i, but the slight variance doesn’t translate to any perceivable difference in practicality.

Up front, there is plenty of space for driver and passenger, with a wide array of seat adjustability offering nearly the perfect position for nearly everyone regardless of shape or size.

Storage options include a generous door pocket with separate bottle holder, large central storage cubby, generous glove box, and two cupholders sited between the shifter and climate controls.

We love that the wireless smartphone charger is tucked well away just ahead of the cupholders, meaning you don’t have to worry about keys or loose change scratching up your screen, and it doesn’t eat into any of the other storage options around the cabin.

Being a coupe, you wouldn’t expect heaps of room in the second row, and the BMW 4 Series certainly doesn’t defy expectations in this regard.

Adult passengers can get in the back easy enough, thanks to auto-folding front seats, but once there, head- and shoulder-room can be a bit tight, while legroom is dependent on the height of front passengers.

We’ve certainly been in worse back seats though, and the deeply recessed seats help alleviate some of the headroom issues, but its not a space for the claustrophobic.

Open the boot and the 4 Series will swallow up to 440 litres of volume and, thanks to the wide space, can easily accommodate a set of golf clubs or weekend luggage for two.

The second row is divided 40:20:40, so you can fold down the middle to transport skis (or timber from Bunnings) while still ferrying four.

Folding the rear seats down will increase your cargo volume, but the aperture between the boot and cabin is quite small, so you might want to keep that in mind before heading to Ikea.

BMW’s new 4 Series range is available in three flavours, kicking off with the 420i for $70,900 before on-road costs, which is powered by a 2.0-litre turbo-petrol engine (more on that below).

Standard equipment includes sport seats, LED headlights, a 12.3-inch digital instrument cluster, push-button start, automatic wipers, Alcantara/Sensetec (vinyl-like) interior trim, three-zone climate control and 10-speaker sound system, but it’s the inclusion of an M Sport package and 19-inch wheels that really elevate the look of the new 4 Series to a real sporty model.

The latter two were options in the previous generation, but so many customers (we’re told close to 90%) opted for the sportier looks that BMW just decided to bundle them into the asking price.

The 420i also comes fitted with a 10.25-inch touchscreen multimedia system that includes digital radio, satellite navigation, wireless smartphone charger, and wireless Apple CarPlay AND Android Auto (finally some love for Samsung owners!).

It’s remarkable then, that the new 420i is actually almost $4100 cheaper than the model it replaces, while also boasting more equipment, safety and torque.

Stepping up to the 430i increases pricing to $88,900 ($6400 pricier than before), while also adding more equipment such as adaptive dampers, keyless entry, surround-view camera, M Sport brakes, leather interior and active cruise control.

Outputs from the 2.0-litre turbo-petrol engine are also increased in the 430i (again, more below).

The current king of the 4 Series range until the M4 lands early next year is the M440i, priced at $116,900, but includes a 3.0-litre inline six-cylinder engine and all-wheel-drive grip.

On the outside, the M440i can be distinguished by the standard inclusion of BMW’s Laserlight technology, sunroof and heated front seats, as well as ‘Cerium Grey’ colouring for the kidney grille, tailpipe shrouds and side-view mirrors.

Being a German model, there is (of course) a smattering of options available – including remote engine start and a heated steering wheel – but none jump out as crucial or ‘must have’ in any way.

We appreciate that the base 4 Series looks largely the same as its more expensive siblings, while also offering all the key equipment you’d want out of a premium sports coupe in 2020.

This new ‘4Matic’ all-wheel-drive SL63 features AMG’s (M177) 4.0-litre twin-turbo V8, superseding the previous rear-wheel-drive SL’s similarly configured 5.5-litre unit.

Hand built by one AMG technician from start to finish, it produces 430kW (around 580hp) from 5500-6500rpm and 800Nm across a broad plateau from 2500-5000rpm.

It’s something of a mechanical masterpiece, and the previous seven-speed auto transmission, driving the rear wheels only, has been replaced by a nine-speed dual-clutch auto (with wet multi-disc start-off clutch) sending drive to all four wheels via Merc’s ‘4Matic’ AWD system.

Both the entry-level and mid-tier 4 Series variants (420i and 430i respectively) are powered by a 2.0-litre turbocharged petrol engine.

Under the bonnet of the 420i, the engine produces 135kW/300Nm, while the 430i ups the ante to 190kW/400Nm.

The flagship (at launch) M440i meanwhile, scores a 3.0-litre turbo-petrol inline six delivering 285kW/500Nm.

All three engines are paired with an eight-speed automatic transmission, with no manual option available on any grade.

The 420i and 430i send drive to the rear wheels, resulting in a zero to 100km/h sprint time of 7.5 and 5.8 seconds respectively, while the all-wheel-drive M440i needs just 4.5s.

Stacked up against its German rivals, the 4 Series offers a decent engine line-up, but doesn’t excel at any level compared to the Audi A5 and Mercedes-Benz C-Class coupe.

Mercedes-AMG’s official fuel economy number for the SL63 on the combined (WLTP) cycle is 13.9L/100km, the 4.0-litre twin-turbo V8 emitting 319g/km of CO2 in the process.

On the roughly 300km launch program we covered urban, B-road and some freeway running, returning an (indicated) average of 17.5L/100km. And that reflects some enthusiastic driving along the way.

The fuel tank requires 70 litres of 98 RON premium unleaded to fill it which translates to a theoretical range of around 500km, dropping to 400km using our real-world number.

Officially, the 420i will sip 6.4 litres per 100km, while the 430i is slightly thirstier at 6.6L/100km.

Both aforementioned 4 Series variants will need 95 RON at the bowser.

The heavier and more potent M440i needs 7.8L/100km, while also using the more expensive 98 RON fuel.

We only drove through Melbourne country roads in our brief time with all three grades of the 4 Series and could not ascertain a reliable fuel economy figure.

Our driving did not cover an extended freeway journey or any inner-city driving, so check back to see if the quoted figures hold up to scrutiny once we get more time with the car.

I recall driving the AMG SL65 around the backroads of Tassie a few years ago and that twin-turbo V12 monster famously packed 1000Nm of torque, while this car ‘only’ has 800.

But there comes a point where enough is enough… and this is enough!

With maximum torque available from 2500-5000rpm and peak power (430kW) on call from 5500-6500rpm there’s always stupendous acceleration available with a squeeze of your right foot.

Claimed 0-100km/h time is supercar fast at 3.6 seconds, while top speed is a toupe-troubling 315 km/h. And that’s electronically limited!

A typically ferocious engine noise and howling exhaust note accompany rapid progress and shifts from the nine-speed dual-clutch transmission are quick and positive, not to mention especially enjoyable using the steering wheel-mounted paddles.

There are six ‘AMG Dynamic Select’ drive programs from Comfort through to Race, the latter including a Drift Mode, which we didn’t experiment with. Nor did we dip into the ‘AMG Track Pace’ system for circuit-focused mapping and timing

However, far from drifting, the grippy Michelin Pilot Sport 4S rubber (275/35 fr - 305/30 rr) plants the car securely with the all-wheel-drive system and electronic locking rear diff playing their part.

I found the perfect set-up was in the ‘Individual’ mode with the engine, transmission and steering in racier settings and the suspension in ‘Comfort’. The adaptive damping in this configuration mixes smooth ride compliance with sharp dynamic response.

The car’s aluminium space frame chassis is part of a body structure mixing aluminium, magnesium, fibre composites and various strength steels.

Torsional rigidity is claimed to have been improved by 18 per cent and despite the lack of a roof the SL feels tight and solid.

Suspension is by alloy double wishbones front and rear with adaptive damping and active hydraulic anti-roll stabilisation standard (so, no physical anti-roll bars).

At the same time the 4Matic AWD system is able to vary torque distribution up to 100 per cent to the front or rear axle depending on where drive can be put to best use.

The speed sensitive, variable ratio, electronically controlled steering is accurate and turns in beautifully with good road feel. No doubt assisted by electric rear steering able to adjust the angle of the rear tyres by up to 2.5 degrees.

All this adds up to a hugely impressive package that, despite its 1970kg kerb weight, feels agile, athletic and able to attack corners like an overgrown hot hatch, putting its power down with unwavering authority.   

While indecently fast the SL63 can also stop rapidly with the AMG high-performance braking system standard. 

Huge composite ventilated and cross-drilled discs (390mm fr - 360mm rr) are clamped by six-piston fixed alloy calipers at the front and single-piston units at the rear. They wash off speed calmly and consistently with perfect pedal feel.

Even at highway speeds, particularly with the windows up, normal conversation is easy with the roof down. But if you need to raise (or lower) it, the operation takes 15 seconds and is possible up to 60km/h. 

Under the heading of miscellaneous observations, the turning circle is a not insubstantial 12.8m, so beware in the car park.

A front axle lift function is a welcome standard feature, raising the car’s nose 30mm with the press of a button. And lift locations are stored in GPS data, so the car will subsequently remember to lift itself at the same place, even if you don’t! 

Heating and cooling for the front seats combined with the heated steering wheel and Air Scarf neck warming makes winter top-down driving a pleasure.

The digital instrument display is not only crystal clear, it can be changed through multiple configurations, including a tunnel-like graphic for engine revs as well as specific readouts for speed, g-force, the lot.

At the same time, the central media screen’s angle can be adjusted to better cope with reflections and the windscreen wiper system Merc calls ‘Magic Vision Control’ channels fluid along the wiper arms onto the rubbers, which isn’t new, but works spectacularly well here.  

Anything wearing a BMW badge promises a fun and engaging drive, after all the brand’s tagline used to be the ‘ultimate driving machine’, which is exacerbated in a sporty two-door.

Luckily then, the 4 Series delivers the goods and is a thoroughly enjoyable drive in all three grades.

Taking the already brilliant new-generation 3 Series as a base, BMW has made the 4 Series lower, and added additional stiffening in the front and rear for a taught and agile handling machine.

The rear track is also increased, while the front wheels have more negative camber to help with mid-corner grip.

Though the 420i and 430i might not draw any headlines, they 2.0-litre turbo-petrol pair are fun to steer and precise with their inputs.

The 420i especially doesn’t have the punch to match its aggressive looks, but is perfectly capable at slower speeds and still a delight to tip in a corner.

The 430i meanwhile, delivers more thrills thanks to its more potent engine, but it can get a bit trashy higher in the rev range.

However, the pick of the bunch for us the M440i, not only for its extra spicy engine, but also the assurance of all-wheel drive.

Now it might be sacrilege to some to not have a rear-drive BMW, but the rear-biased xDrive system in the M440i is wonderfully tuned to deliver the same sort of natural driving characteristic of a two-wheel-drive model.

Undoubtedly the near-perfect weight distribution helps with this, while the wonderfully low driving position means the whole car feels like it pivots around the driver when turning the wheel.

The M Sport differential in the rear is also great at propelling out you out of the bends, while the adaptive suspension also has great variability between comfort and sport settings.

If we had any criticism with the driving experience? We’d have liked a bit more aural theatre, but BMW have to save the louder pops and crackles for the full-fat M4, right?

A big caveat here though is that we have yet to experience the new 4 Series in a suburban setting, with our launch route taking us directly to some twisty country roads.

We also never got to drive the 4 Series in a freeway setting, meaning all of the driving was done in twisty country roads where you would expect a BMW to excel.

BMW’s 2021 4 Series has not been crash tested by either Euro NCAP or ANCAP, and does not wear an official safety rating.

However, the mechanically related 3 Series sedan was awarded a maximum five-star rating when it was examined in October 2019, but do keep in mind that the child occupant protection scores could vary wildly due to the 4 Series’ coupe shape.

The 3 Series scored 97 per cent for the adult occupant protection test, and 87 per cent for the child occupant exam. Meanwhile, the vulnerable road user protection and safety assist tests yielded an 87 and 77 per cent result respectively.

As standard, the 4 Series is equipped with autonomous emergency braking (AEB), forward collision warning, lane departure warning, rear cross-traffic alert, reversing camera, and front and rear parking sensors.

The SL63 4Matic+ will be covered by Mercedes-AMG’s five-year/unlimited km warranty, with roadside and accident assistance included for the duration, both of which are expected in this category. 

Maintenance intervals are 12 months/20,000km, and a fixed-price service plan lists an average of $1583 for each of the first three visits to the workshop. Not exactly small change, but not unheard of in this part of the market.

Like all new BMW models, the 4 Series comes with a three-year/unlimited kilometre warranty.

However, the benchmark for premium brands belongs to Mercedes-Benz, who offer a five-year/unlimited kilometre warranty, while Genesis matches the time period but limits travel to 100,000km.

Scheduled servicing for the 4 Series occurs every 12 months or 16,000km.

At the time of purchase, BMW offers a five-year/80,000 ‘basic’ service package that covers scheduled changing engine oil, filter, spark plugs and brake fluids.

This package costs $1650, which works out to be a very reasonable $330 per service.

A more thorough ‘plus’ plan is also available for $4500 that also covers brake pads/discs, clutch and windscreen wiper replacements over the same five-year/80,000km period.