Audi RS Q8 vs Mercedes-AMG GLC63

What's the difference?

The Audi RS Q8 Performance is a lot - of everything. It offers lots of power, lots of performance, lots of space and lots of luxury. But it’s also a lot of money, and at more than $250k it’s not going to be on everyone’s shopping list. It’s a very niche proposition for a small group of buyers. For those select few, those who want a lot of everything and who crave the ultimate of whatever product they’re buying, then the RS Q8 Performance is going to be a very tempting proposition - even if they never set any lap record in it.

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

Obviously, I had nothing to worry about. The GLC 63 S is the same boisterous, silly car I drove 18 months ago, just with a few new bits to improve the package. As ever, the GLC 63 S is all about the experience - big noise, huge grip but all in comfort with plenty of gadgets.

The only real issues are price, service pricing and the length of the warranty. The first two probably won't bother most owners and one hopes the third won't be problem, but it would be nice if the length was reflected in the price.

If you care about badge, it has impeccable credentials, the AMG stripes and that plate on the engine with the builder's name. They're good credentials. The GLC 63 S has some very determined and capable competition, but none of them blend the speed, overall comfort and sheer sensory silliness of the AMG.

We don’t refer to ‘facelifted’ cars for no reason, the RS Q8 Performance has a number of visual changes.

These include a new Audi ‘singleframe grille’ and new front bumper design, with a new Matt Carbon trim package available to highlight that.

There’s also a new rear bumper design as well as new digital daytime running lights at the front and digital OLED lights at the rear.

The unique forged alloy wheels are another design change, but also bring a functional element. Measuring 23 inches they do a good job of filling out the wheel arches and give the RS Q8 Performance a purposeful stance and good proportions. But they are also 5kg lighter per wheel than the 22-inch rims on the RS Q8, saving unsprung weight to help the ride and handling.

Inside, Audi hasn’t made any dramatic changes to the design, which is fine because the brand does some of the best cabins on the market in terms of look and feel.

What is new is an aluminium inlay and an optional RS interior design package which provides a unique finish to the seats, with contrasting stitching, for an additional $4100.

As before, the GLC 63 S comes in wagon and couple bodystyles. Little has changed, with just the usual tweaked front and rear bumpers and mildly redesigned headlights.

All the good bits have remained, like the 'Panamericana' grille from the AMG GT monsters, the jet wing-inspired front bumper and plenty of open space to feed the radiators and intercoolers.

Neither the wagon nor coupe is a pretty machine, but no mid-size SUV is much of an oil painting, with the exception of the Jaguar F-Pace.

The 'Night Package' is still a standard inclusion, blacking out various bits and pieces and looking good when allied with the dark alloys. They both look tough, though, which is classic AMG DNA.

Inside is pretty much the same as before, with just two obvious changes. The new Alcantara-trimmed steering wheel, again from the AMG GT, and also on the C 63 S, joins the party with a more expensive look and feel.

And the new MBUX screen is wider and looks much more at home in a $165,000-plus car. It's still a bit old-feeling, but the digital dash adds a bit of techno-style while the garish speaker covers don't.

While it’s easy to get swept up in the power and speed of the RS Q8 Performance, it’s important to remember that it’s an SUV and it needs to offer ‘utility’ as well as ‘sports’. 

With that in mind, the front seat occupants are well looked after with supportive and comfortable sports seats, with a good amount of small item storage spaces. 

The rear seats are surprisingly comfortable, despite the sloping roofline of this ‘coupe-style’ SUV. Audi has cut recesses into the ceiling to create more headroom, so it will be fine for anyone under six-foot tall. Despite there being five seat belts, this is realistically more of a four-seater for adults, although three smaller kids could squeeze across the back.

There’s also a pair of cupholders, two USB-C ports, a 12-volt outlet and your own climate controls for the rear passengers.

As for the boot, again it loses some volume because it’s not a wagon-style SUV, but there’s still a decent, square floor space with a claimed 605 litres of capacity.

So, overall the Q8 obviously isn’t the most practical version of an SUV, but it does well given its focus on style.

A family of four will love any GLC. The wagon's extra headroom over the coupe is useful if not life-changing, while the knee, leg and foot room are generous. Front seat passengers enjoy comfortable seating as long as you're not too keen on pudding.

Underneath, the upward sweep of the centre console is a pair of cupholders and a wireless charging Qi pad that will fit larger phones. Under the split armrest is a small but handy console bin, inside which you'll find USB-C ports.

Two more USB-C ports in the rear join a 12-volt socket and there are also climate controls for the rear seat passengers. The centre armrest pops open with a shallow, carpet-lined tray and two cupholders pop out the front. Each of the four doors has a bottle holder, too.

The boot space is unchanged for each bodystyle - 550/1600 litres for the wagon and 500/1400 litres for the coupe. Both have high loading lips, which is something to consider if you're hauling heavy things about or have trouble lifting items to a reasonable height.

As before, we get two bodystyles and the high(er) performance version, the GLC 63 S (a 'base' GLC 63 is available in other markets). Mercedes followed everyone else's lead and realised nobody would buy the skim milk version.

Unfortunately, that translates to the highest sticker price of the three, with the wagon coming in at $164,900, and the coupe at $171,900, before on-road costs.

That doesn't seem to hurt Mercedes too much with other cars in the range, but it's a significant difference. Incidentally, both prices are up by about $3000.

It's loaded, though - 21-inch wheels, multi-zone climate control, air suspension with dynamic dampers, electric and heated front seats, active cruise control, head-up display, reversing camera, around-view cameras, sat nav, front and rear parking sensors, keyless entry and start, electric tailgate, Nappa leather and wood trim, active LED headlights, auto wipers, auto parking, roof rails, sunroof, DVD player, and TV tuner, but no spare tyre, just a repair kit.

A Burmester-branded 13-speaker sound system is powered by Mercedes' spangly MBUX system on a new 10-inch touchscreen, which is much nicer than the old software and hardware combo.

MBUX offers deeper integration with the car's systems. The 'Themes' function is like a series of shortcuts to set the car up for a particular mood, but let's face it, most GLC 63 S drivers are just going to find the 'Race' function and go for it.

MBUX also has Apple CarPlay and Android Auto, but via USB only.

This is the latest iteration of Audi’s twin-turbo 4.0-litre V8 petrol engine - and it’s a beauty.

While this engine is used in a variety of models, for the RS Q8 Performance Audi has taken power to 471kW with 850Nm of torque, which, as mentioned earlier, makes it the most powerful internal combustion engine Audi has ever offered in a production car.

That’s also a big boost over the previous RS Q8, which managed 441kW/800Nm, and is only just shy of the 485kW/850Nm offered by its ‘cousin’, the Porsche Cayenne Turbo GT.

Audi claims that the RS Q8 Performance will launch 0-100km/h in just 3.6 seconds and keep going to an electronically limited top speed of 250km/h. We tried to test the acceleration time on a closed circuit, but driving into a very strong headwind the big SUV could manage only 4.4 seconds - which is still a very quick time given its size and luxury.

The engine is paired to an eight-speed automatic transmission and Audi’s trademark quattro all-wheel-drive system to help smoothly transmit so much power to the road.

An AMG 4.0-litre twin-turbo V8 brings the thunder, with a massive 375kW and 700Nm of torque. That's plugged into a nine-speed MCT (multi-clutch as opposed to twin-clutch) transmission and Merc's '4Matic+' all-wheel drive system.

With all that power and grip, you'll crack the ton in a supercar-baiting 3.8 seconds. One little point to note is the engine has active mounts.

Should you fancy turning your tinny into a landspeedboat, you can tow up to 2000kg for a braked trailer, and 750kg unbraked.

Unfortunately you don’t get the most powerful production engine without some trade-off, and for the RS Q8 Performance that means significant fuel consumption. The official fuel economy rating is a very thirsty 12.2L/100km, but that's the best-case scenario too. If you partake in some spirited driving that unleashes the full potential of the engine will result in a higher rate of premium unleaded being consumed by the big V8. We saw returns in the high teens across our time, but that was largely open road driving, so we’ll reserve final judgement for an extended test drive across more varied conditions.

Thankfully there’s a fairly large 85L fuel tank, so if you can hit the claimed average you can get a theoretical 696km of range.

Mercedes reckons you'll get 12.2L/100km on the combined cycle which seems laughable at first and then you see what it actually does. To be fair, the car I drove on the launch copped a hammering and was hovering around the 17.0L/100km, with the start-stop and coasting functions playing only cameo roles.

Obviously the RS Q8 Performance is all about speed, Audi made its intention clear by sending it to the Nurburgring to set a new SUV lap record for an SUV. But the reality is most owners are unlikely to hit the racetrack in the RS Q8, so what’s it like on the road?

In a word? Impressive.

While the engine is undoubtedly the star attraction offering up so much effortless performance, the RS Q8 Performance wouldn’t be so quick around the Nurburgring or as nice to drive on the road without its highly advanced chassis systems.

It has an array of technology to help it handle, it has active air suspension, adaptive dampers, active roll stabilisation and all-wheel steering, which help to make this big SUV handle like a much smaller car.

The suspension does a remarkable job of providing a compliant ride on such large alloy wheels, while also providing responsiveness.

The handling is certainly helped by the all-wheel steering, which gets the rear wheels to turn in the opposite direction to the fronts at low speed (below 50km/h), but in the same direction at high speed (above 80km/h), making the big SUV feels much more direct when changing direction.

As for the overall experience, that’s helped by Audi’s surprising decision to actually remove some of the sound insulation, which allows you to hear the engine even more than you ordinarily would. This really plays to the dynamic nature of the RS Q8 Performance.

Like any V8-powered AMG, the twin-turbo engine absolutely dominates the GLC 63 S. Even at walking speeds you can feel the serious firepower on offer, just a flex of your ankle away.

The figures are colossal - 375kW (over 500 horsepower) and 700Nm pushing around two tonnes of mid-sized SUV. Its famed bark is bettered only by Jaguar's completely unhinged, and surely borderline illegal, 5.0-litre supercharged V8.

You need to know you've got plenty of tech underneath you to make this stick to the road. The 21-inch alloys are wrapped in 265/40s at the front and 295/30s at the back, Continental Cross Contacts if you're interested.

They should - and would - ruin the ride, but the standard fitment of air suspension means that in normal driving, the GLC 63 S is firm but comfortable. A BMW X3 M is much harder, especially at the rear, going without the complex and heavier air set-up.

The air suspension is probably the pivotal piece of chassis tech that makes this car so versatile. While it's got driving modes up the wazoo - including the new 'Slippery' mode - it's a perfectly agreeable daily driver.

Leave it in comfort, accept that it has a firm ride and you're in good shape for the school run or the commute. You just sail along on a light throttle because there is virtually no turbo lag.

Whack it in Race and you can attack your favourite empty, bendy road with all the grip you could ever need.

The steering is remarkably light and direct for such a chunker and the optional carbon ceramic brakes were never bothered by what I could throw at them.

The V8 roars and spits and crackles, the gearbox shifting seamlessly up and down through the ratios. It's blissfully silly.

In a way, it's a velvet fist in an iron glove - comfortable inside but happy to headbutt the horizon with little provocation.

I'd prefer it if the transmission was a bit more decisive on slow speed shifts and you'll have to prepare yourself for a lot of wearying road noise on long trips. The latter is the price you pay for a ton of grip.

All GLCs have nine airbags, ABS, stability and traction controls, traffic sign recognition, around-view cameras, reversing camera, rear cross traffic alert, blind spot monitor, forward AEB, forward collision warning and tyre pressure monitoring.

There are also three top-tether mounts and two ISOFIX points.

The GLC scored a maximum five ANCAP stars in January 2016.

Despite the extra power and fancy new brakes, the RS Q8 Performance costs the same to service as the existing RS Q8.

That means $4690 for Audi’s five-year service plan, and $5720 for the Audi Advantage.

The latter package includes an extra two-year, unlimited kilometre warranty on top of Audi’s five year/unlimited km coverage. It also includes two extra services and two more years of roadside assistance, to keep you covered for seven years total.

That’s good, but it’s still an extra cost when many mainstream brands already offer seven years of coverage as standard.

Mercedes Benz offers a three year/unlimited kilometre warranty with roadside assist which is not really up to scratch for a premium brand. Yes, the cars are complex but they're also expensive, so the investment should come with a commensurate warranty.

Service intervals are generous at 12 months/20,000km (as opposed to the 25,000km of other GLCs) and the capped price servicing means you'll know what you're paying.

Mercedes offers you the choice of an up-front payment or pay-as-you-go. Upfront ranges from $4050 for three services, $6100 for four, and $6850 for five.

If you go with PAYG, three services is a hefty $5000. Basically, each service is at least a grand when averaged out over time and that's pricey.

Service inclusions differ between your chosen method, but only slightly. The pricing includes filters, oil and, unusually, spark plugs and brake fluid, but that's small comfort.