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.
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.