Porsche 911 Cabriolet vs Mercedes-AMG GT Roadster

20 Aug, 2019 4:15pm

The brand new Porsche 911 Cabriolet takes on the updated Mercedes-AMG GT Roadster

With summer in full swing, there’s a number of new high-profile convertibles hitting the market, starting with the Porsche 911 Cabriolet. This drop-top follows in the wheeltracks of the Coupé, with the famous sports car now in its eighth generation.

There’s also much more tech underpinning the 911’s new platform, while Porsche has worked hard to reduce the impact of removing the 911’s roof and make this a car that’s befitting of that badge when it comes to the driving experience.

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After more than 50 years of evolution, the 911 in all its forms has staved off the challenge of its rivals. But with this 992 Cabriolet they’re still coming thick and fast, the latest in the form of the updated-for-2019 Mercedes-AMG GT Roadster. The recipe here is traditional AMG, with a V8 engine up front powering the rear wheels for what, we hope, is a beautifully balanced drive.

Both cars have electrically folding fabric roofs, a top speed of 188mph and a price tag comfortably exceeding £100,000. Yet they approach the brief for an exclusive cabrio in decidedly different ways, so let’s find out which is best.

At this level of the market, with cars costing this much, buyers will forgive few faults, so it’ll be an incredibly tough test. 

Porsche 911 Cabriolet

Model:Porsche 911 Carrera 4S Cabriolet
Price: £109,398
Engine: 3.0-litre flat-six twin-turbo, 444bhp 
0-60mph: 3.3 seconds
Test economy: 22.1mpg/4.9mpl 
CO2: 207g/km  
Annual road tax: £465

We’re testing the new Carrera 4S version of the 911 Cabriolet here. So while it’s four-wheel drive when compared with the rear-driven AMG, it brings their respective prices closer for parity, at £109,398. It’s a chunky price tag, but is it worth it?

Design & engineering

Like the 911 Coupé, this 992-generation Cabriolet is based on a new platform that includes more aluminium than ever before to help keep kerbweight down. This stands at 1,635kg for this Carrera 4S, which is unsurprising given the 911’s increase in size over its predecessor.

The Cabriolet is currently offered in Carrera, Carrera S and Carrera 4S guises, all with Porsche’s eight-speed PDK, dual-clutch automatic gearbox – a manual box is promised at a later date.

All models get a 3.0-litre twin-turbo flat-six that’s an evolution of the engine seen in the 991.2 model. New turbos (now specific to each cylinder bank) and updated cooling and injection systems in the latest unit have helped liberate more power and torque, so there’s 444bhp and 530Nm on offer in the 4S.

The transmission is also new, with eight ratios and space inside the gearbox for an electric motor, so hybrid variants of the 911 are in the product plan.

The 911 has a wider track front and rear, which has created a little more space inside, while Porsche’s approach to the interior has changed tack with the 992. There’s a lot more tech, and the infotainment screen and major controls are arranged horizontally in two layers, rather than the central stack of its predecessor. It works well; the ergonomics are good and the driving position superb – the AMG GT is more compromised.

Removing the roof has obviously required some chassis strengthening to retain as much structural rigidity as possible, and while the Cabriolet is 70kg heavier than the coupé, it also adds to the experience.

You can drop the roof electrically in 12 seconds at up to 30mph, while the canvas features extra insulation to improve refinement. That’s an element that’s been improved for this new car, while there’s also more standard kit – and so there should be at this price.

Sat-nav, Apple CarPlay, LED lights, heated seats, adaptive suspension, parking sensors, a reversing camera, AEB, climate and cruise control are all standard.

Driving

A huge part of any cabriolet’s appeal centres on the roof-down driving experience, and the 911 is about as complete as they come.

Convertibles are partly about basking in the exhaust note, and while the AMG offers a superbly characterful V8 bellow, the 911’s soundtrack isn’t quite as rich, even with the £1,844 sports exhaust fitted. The bassy bark is overlaid with turbo noise – it’s the way 911 development has gone, but it does mean there’s plenty of performance.

Despite a 32bhp power deficit and 100Nm less torque than the AMG, the 911’s excellent launch control and four-wheel-drive traction meant it romped from 0-60mph in 3.3 seconds.

With an extra ratio in its gearbox, the 911’s in-gear times are slightly skewed against the Mercedes’, but the Porsche feels equally potent. The gearbox is great, with sharp changes and no perceptible interruption to drive. Downshifts are beautifully smoothed out with an automated blip. There’s a little more lag than the Mercedes, but the engine is torquey and linear.

Where the 911 really shines compared with the AMG is in the way it rides and handles. It’s firmer, but much more comfortable, while the inevitable body shake you get from a convertible is well contained.

Even in the firmer of the two suspension modes the damping feels slicker, finessing bumps that the AMG thunders over. It’s impressively composed and generates more grip than the Mercedes. You also know more about the grip level and have a better connection with the car thanks to the steering – the weighting in particular is much more natural.

Practicality

Convertibles like these generally see practicality as a secondary concern, with usability centring more on features like the 911’s wind deflector. It’s electric and does a good job of reducing turbulence when the roof is down.

Of course, with two small back seats for kids or extra luggage, the 911 has a little more practicality than the Mercedes, even if the 132-litre boot in the nose is less than the GT’s claimed 350-litre maximum. 

Ownership

Porsche didn’t rank in our Driver Power owner satisfaction survey this year. However, given that much of the 911’s tech is shared with other models – its infotainment is similar to the Cayenne and Panamera’s, for example – and the 3.0-litre engine proved to be reliable in the previous-generation 911, then this 992 should be no different.

There’s more safety tech on offer than ever as well. Autonomous braking is fitted, there are six airbags plus pop-up roll bars that deploy from behind the rear seats if the electronics sense that the car is going to flip over, as with the GT. Lane-keep and blind-spot assist are optional, at £749 and £581 respectively. 

Running costs

Fuel economy won’t be much of a concern for buyers looking at a £100,000-plus convertible sports car. But cruising range might, and both cars here are similarly matched. The 911 returned 22.1mpg, and with a 67-litre tank will manage a max 326 miles on a run.

The AMG GT did slightly less well, at 20.9mpg, but will cover around 345 miles thanks to its larger fuel tank. Petrol costs based on these numbers stand at £3,253 and £3,440 for 12,000 miles of use.

Testers’ notes: “How can you tell the difference between the rear-wheel-drive Carrera S and the all-wheel-drive Carrera 4S in our pictures? Simple, the latter has silver air vent slats on the engine cover.”

Mercedes-AMG GT Roadster

Model:Mercedes-AMG GT Roadster
Price: £115,875
Engine: 4.0-litre V8 twin-turbo, 469bhp 
0-60mph: 4.1 seconds
Test economy: 20.9mpg/4.6mpl 
CO2: 261g/km
Annual road tax: £465

A facelift for the Mercedes-AMG GT Roadster has kept it fighting fit against newer rivals like the 911 Cabriolet, with some significant updates to improve its appeal. At £115,875 it’s dearer than even the 911 Carrera 4 S Cabriolet, but price isn’t as much of an issue as ability at this level.

Design & engineering

The GT is based on an aluminium chassis with double wishbone suspension all-round – while the 911 uses more aluminium than ever, there’s still steel present. The AMG also uses some magnesium components, yet it still weighs more, at 1,690kg, than the 911’s 1,635kg.

This difference is offset by the extra firepower from the AMG’s thunderous V8. In GT form the 4.0-litre twin-turbo engine produces 469bhp and 630Nm of torque. It comes with a seven-speed dual-clutch transmission and drives the rear wheels.

The AMG’s looks were subtly updated with new LED headlights and tail-lights. However, the changes in the cabin are more important. These include an updated infotainment system and new buttons for selecting drive modes and other parameters.

A fully digital dashboard is now standard, while other kit matches the Porsche’s: parking sensors, a rear camera, autonomous braking, climate and cruise control, heated leather seats, sat-nav, Apple CarPlay and Android Auto are all included.

However, where it can’t match the 911 is for quality. There’s too much cheap-looking and feeling black plastic inside. It has lots of leather, but fewer surfaces are coated in it than in the Porsche, which feels higher-quality and better built. The mix of textures inside the GT means it doesn’t feel as premium.

Driving

The AMG GT’s ride is firm, so those plastics vibrate more on bad road surfaces. Adaptive dampers aren’t standard, unlike on the Porsche, and cost £1,495 extra. On 19-inch wheels the AMG feels less forgiving, because it fidgets and never really settles. And yet the set-up is also softer than the 911’s.

Mercedes has recalibrated the steering so it’s much lighter than before. There’s plenty of grip, but not as much poise as in the 911. Because the steering is so fast and light, the AMG turns extremely quickly, and the softer set-up means there’s some roll. The chassis and steering aren’t as communicative as the 911’s, and the car can feel nervous. It takes some getting used to, and even when you think you’ve got the measure of it, you sometimes find yourself taking separate and distinct bites at corners, because the Mercedes doesn’t have the same easy flow as the Porsche.

There are no complaints about how the GT Roadster romps down the road when you’re on the power, though. With the roof down and the exhaust set to its louder setting, the V8 rumbles aggressively. There’s very little turbo lag and the engine feels more urgent than the 911’s as soon as you accelerate.

The AMG did 0-60mph in 4.1 seconds, which was 0.8 seconds slower than the 911 – but that’s not much of a surprise given the GT has more power that gets sent through just two driven wheels. The in-gear times show that: in the lower ratios it was pretty much honours even, but in the taller gears the AMG was actually slightly quicker than the 911.

The gearbox is brilliant, with little to separate the two car’s transmissions, and the AMG’s double- clutch unit rifles through the box with clinical ease. Downshifts unlock another level to the noise, and the pops in Sport+ mode from the quad exhausts fit the hot-rod vibe well. Given the powertrain’s personality and ability, it’s all the more frustrating that the chassis can’t quite match up.

Practicality

Mercedes claims the GT offers between 165 and 350 litres of boot capacity. It’s a wide but shallow space, whereas the 911’s load bay in the nose is a little more regular. There’s enough room for weekend bags in the Mercedes though, which should be enough practicality.

It’s a good job the GT has a reversing camera, because rear visibility isn’t great, even with the roof down – thank the car’s long, low proportions for that.

The cabin is more cramped than the 911’s, and it doesn’t boast any extra space because there are no rear seats, but there’s just enough storage.

Ownership

We haven’t exactly seen a stunning performance from Mercedes in our Driver Power owner satisfaction survey, finishing 26th our of 30 brands, which might not be what you’d expect from a premium brand.

Neither the GT nor the 911 have been crash-tested by Euro NCAP, but safety is good, with six airbags and autonomous braking both standard. However, as in the Porsche, lane-keep and blind-spot assist are extra and come as part of a £1,695 pack.

Running costs

Many people purchase on finance, so monthly PCP prices could drive a buying decision. For cash buyers the Porsche holds on to more money, with an impressive 62.2 per cent retained value, according to our experts. This means it’ll be worth £68,046 after three years.

The GT costs more, but will hold on to less, rated at 49.6 per cent. This equates to a higher loss: £57,474.

Servicing will also be pricey, with three checks on the 911 costing £2,670 compared with £49 per month over three years for three checks on the AMG, which comes to £1,764. However, while the 911 is costlier, it might only need servicing every two years compared with annual check-ups for the Mercedes.

Testers’ notes: “The AMG’s roof can be raised or lowered electrically in 11 seconds at up to 31mph. With the top down it’s as refined as the 911. The Airscarf system also helps to warm your neck in winter.”

Verdict

First place: Porsche 911 Cabriolet

There are a few small flaws, but the 911 Cabriolet is about as competent as convertible sports cars come. Admittedly, it doesn’t excite in quite the same way as the AMG, but it’s as fast, rides and handles better and feels higher-quality inside, with a little more practicality. It’s basically all square on infotainment and equipment, so the Porsche’s prowess on UK roads sees it score higher than the GT. 

Second place: Mercedes-AMG GT Roadster

The AMG’s engine is reason enough to buy it; factor in the looks and the theatre, too, and it’s a great convertible, but it’s not the most competent sports car here. Its motor and gearbox are great, but the super-fast and oddly light steering, combined with the lumpy ride and some shake through the chassis, mean it’s not ultimately quite as rewarding as the 911. It’s ability, not cost, that’s the issue.

Other options for similar money...

New: Audi R8 V10 Spyder

Audi R8 V10 - front cornering

Price: £136,985
Engine: 5.2-litre V10, 562bhp

For a little more than the GT you get quite a bit more power and stunning supercar looks. The mid-engined R8 V10 Spyder sounds great, and with four-wheel drive is as quick as the 911. Be prepared to sacrifice a little usability for the styling.

Used: Mercedes SLS AMG

Mercedes SLS AMG GT front tracking

Price: £121,850
Engine: 6.2-litre V8, 563bhp

The SLS is the GT’s predecessor. All AMGs are now turbocharged, but the SLS was one of the last remaining non-turbos, with its glorious 563bhp 6.2-litre V8. In the Roadster you can hear the noise even more clearly, and it looks great.

Figures

Porsche 911 Carrera 4S CabrioletMercedes-AMG GT Roadster
On the road price/total as tested£109,398/£120,998£115,875/£127,295
Residual value (after 3yrs/36,000)£68,046/62.2%£57,474/49.6%
Depreciation£41,352£58,401
Annual tax liability std/higher rate£7,997/£15,993£8,413/£16,825
Annual fuel cost (12k/20k miles)£3,253/£5,422£3,440/£5,734
Insurance group/quote/VED50/£1,056/£46550/£1,151/£465
Cost of 1st/2nd/3rd service£625/£950/£1,095£49/month (3yrs)
Length/wheelbase4,519/2,450mm4,544/2,630mm
Height/width1,299/1,852mm1,259/1,939mm
EngineFlat-six/2,981ccV8/3,982cc
Peak power/revs444/6,500 bhp/rpm469/6,000 bhp/rpm
Peak torque/revs530/2,300 Nm/rpm630/1,900 Nm/rpm
Transmission8-spd PDK/4wd7-spd DCT/rwd
Fuel tank capacity/spare wheel67 litres/repair kit75 litres/repair kit
Boot capacity132 litres165-350 litres
Kerbweight/payload1,635/430kg1,690/250kg
Turning circle11.2 metres12.5 metres
Basic warranty (miles)/recovery3yrs (unlimited)/3yrs3yrs (unlimted)/3yrs
Driver Power manufacturer/dealer posN/A/N/A26th/13th
NCAP: Adult/child/ped./assist/starsN/AN/A
0-60/30-70mph3.3/2.8 secs4.1/3.8 secs
30-50mph in 3rd/4th2.0/3.1 secs2.0/2.7 secs
50-70mph in 5th/6th/7th3.6/5.2/8.5 secs3.1/4.0/6.3 secs
Top speed/rpm at 70mph188mph/1,600rpm188mph/2,000rpm
Braking 70-0/60-0/30-0mph45.5/34.2/8.4m49.6/36.0/8.7m
jumbo-bg economy/range22.1/326 miles20.9mpg/345 miles
Govt urban/extra-urban/combined 25.0-26.6mpg23.0-23.3mpg
Govt urban/extra-urban/combined 5.5-5.9mpl5.1-5.1mpl
Actual/claimed CO2/tax bracket295/207g/km/37%312/261g/km/37%
Airbags/parking sensors/cameraSix/yes/yesSix/yes/yes
Auto box/lane keep/blindspot/AEBYes/£749/£581/yesY/£1,695*/£1,695*/y
Climate/cruise/leather/heated seatsYes/yes/yes/yesYes/yes/yes/yes
Met. paint/LEDs/keyless/pwr tailgate£876/yes/£387/no£945/yes/£2,995*/no
Sat-nav/digi dash/DAB/connectivityYes/yes/yes/yesYes/yes/yes/yes
Wireless charge/CarPlay/Android AutoNo/yes/noNo/yes/yes
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