Engine options, top speed, acceleration and refinement

Like all full-fat Mercedes-AMGs, the A45 S has a ‘race start’ launch control system that requires you to use Race driving mode to access it. The way in which the car takes off under that all-corner, wheelspin-optimised electronic governance blends savagery and smoothness to remarkably addictive effect.

The bald numbers we recorded for the car are all suitably monumental – except, perhaps, for the most important one (0-60mph). On a slightly damp surface, the car hit 100mph from rest in just 9.3sec. The Audi RS3 Saloon we performance tested three years ago was more than half a second slower than that and a Honda Civic Type R was fully three seconds slower. The A45 S needed just 3.3sec to get from 30mph to 70mph through the gears, whereas an Alpine A110 needed 3.8sec.

Cross-country pace is limited almost entirely by your sense of social responsibility, because the car has excellent grip, traction, balance, composure and acceleration

This is, by almost any marker, a very fast car and justifies its price quite easily in simple performance terms. It narrowly missed the chance to prove itself a sub-4.0sec 0-60mph operator in those slightly imperfect conditions, though. Its fastest oneway run on the day was 4.07sec, but on a warmer, drier day, that showing would certainly suggest times starting with a three are possible.

The four-cylinder engine supplies plenty of audible theatre, which you can adapt and change a little using its various drive modes, and its angriest pops and whooshes are always entertaining to listen to. But if our performance numbers leave any room to doubt that it is, in every way, the dominant force you might have expected, then getting to know the motor first hand and in detail may not emphatically settle the question.

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There is more than a hint of peakiness about the engine’s production of torque; to be expected, you might think, in light of the fact that it’s operating beyond 200bhp per litre. It doesn’t feel overboosted or troubled by turbo lag, but it’s enough to make you wonder just how much of that peak torque is available when you flatten the accelerator below 4000rpm. That’s not something you ever wonder about Audi’s rampant five-cylinder RS engine, which feels a deal more flexible than the AMG unit – and, almost anyone would concede, also sounds considerably richer and more characterful.

The eight-speed dual-clutch gearbox can make the car’s low-speed manoeuvring behaviour a bit erratic, but it works quickly at pace and its kickdown tendencies can be adjusted according to the chosen drive mode. Brake pedal feel is very good, and the car sheds speed strongly even in slightly slippery conditions, as our test results show.