Speed Week: RS6 vs. SLS Black

The thought that's probably striking you now is the one that struck me when we first divvied up the tests for Speed Week. RS6 vs SLS Black. They're not exactly two peas in a pod, are they? Pity the five-door estate, you're thinking, faced with the task of squaring up to one of the most fearsome track weapons ever to fight its way out of a factory. The SLS Black should be muzzled. This is going to be like a bunny facing down a fox, armed with nothing more than a softly padded paw and a pair of jaunty ears. The RS6 is going to be skinned alive...

We'll come on to how each fared at the track in due course, but I think you have an inkling of how that might pan out. So let's step back from that to start with, because as you've already read, these two didn't magically apparate at the Circuit de Charade. We drove them here across the Alps, and before that, on German 'bahns, conditions that gave us an essential grounding in what each car stands for, what it's capable of.

Words: Ollie Marriage

Photos: Rowan Horncastle

But you know what? The SLS had to work hard every step of the journey to keep pace with the RS6. The Audi, twin-turbocharged and impossibly muscular, blitzes gaps in traffic and does so with minimal effort. In the SLS, you have to be more alert: you can't just slam on the pedal and spear the horizon - you need to think about gears and traction and camber and surface and driving the thing. It's immersive and demanding in a way that the RS6 just isn't. In the Audi, once you've mastered mirror, signal, manoeuvre, you don't need to know much more. The car takes care of everything, supporting you in a quattro cradle, distanced from the actual goings-on by layers of insulation and beefy servos.

Let's leave it at this. In the real world, both accumulate speed with near-equal alacrity, the Audi's torque surplus offsetting the Merc's power and weight advantages, its brotherly arm around your shoulders a genuine comfort on hairy passes that's entirely missing from the blood-and-thunder Mercedes. The Audi makes speed feel safe; the SLS relishes the danger. We saw 175mph in both. In the Audi, it was a nonchalant act, done while I was discussing picture requirements with photographer Dom Romney... in the SLS, I don't remember breathing.

What, then, makes this contest so fascinating is what happened when we arrived at the track. Given that as a road car the Black is at best barely house-trained, you might imagine that it would relish an early opportunity to spank itself backwards into something solid. Presented with the same circumstances, the standard SLS might well do just that - body control isn't its forte.

So I watch as my colleagues approach the SLS Black warily, reading a reputation written in Michelin Cup tyres, carbon trimmings, daft doors and perhaps one of the most exciting road-car engines there has ever been. They know that driving it will allow them to live their Le Mans fantasies, but fear the consequences of getting it wrong. No one fears the Audi. People get in and go fast straight away. I bet plenty of people are going faster around Charade in the RS6 than anything else. I also bet some of them have outbraked themselves once or twice in the process, faintly shocked at just how effective the twin-turbo 4.0-litre V8 is at heaping speed on.

At Charade, the short, stabby gearing is no issue - it just means you get to change gear more often, not that it was a bit noisy when cruising. The drivetrain rattle, unnerving in public places, now just reeks of pedigree motorsport. And the spikiness of its earlier personality, the fidget and jink and weave? Gone. At Charade, the SLS Black is the master. Nothing feels more suited to the circuit nor attacks it so vigorously or so competently. Here is a car that gives you the full endurance racing experience: bucket seat, borderline claustrophobic cabin, endless bonnet, rampant engine. But it isn't frightening - it's friendly.

The RS6 achieves this by soothing your brow and reminding you that it has control, whereas the Black helps you make the right decisions by ensuring the lines of communication are clear and open. The steering - too hyperactive on the road - is now a marvel of clarity; traction is vast and when it does slip, it does so smoothly, with plenty of warning. The chassis balance is exceptional, the brakes more potent and nicer to use than anything else in the pit lane, Formula Ford included. Every apex you clip turns to gold in the SLS Black. It's the one car I want to keep on driving through the night.

I find the SLS Black addictive. This is the car I take for one last blat, just to hear that naturally aspirated 6.2-litre V8 gulp and roar like a T-Rex. But something's wrong - this time, the tune I'm hearing is harsher, barely silenced at all. For a moment, I'm convinced the Merc has managed to shed its entire exhaust from the manifold back, but then from the other side of the pit wall something shoots out to join me on the circuit. Something small and red and impossibly noisy...