With its four-cylinder engine and all-wheel-drive system, the first A45 was not really a car for Mercedes-AMG's established aficionados. But it was never aimed at them. They were already well served by the brand's assorted V8 and V12 saloons, sports cars, SUVs and estates. The racier, cheaper A-Class targeted a younger audience - buyers who wouldn't previously have been in the market for an AMG. It was therefore a hugely important car for Affalterbach, broadening the reach of the brand and providing it (at last) with a hot hatch to rival the German competition. It was succaeressful, too, with twice the original estimate of cars finding buyers. As the most popular AMG model on sale (nearly a thousand were sold last year in the UK), replacing the A45 was not a task to be taken lightly.
The original A45 wasn't beyond improvement, either; while the engine was mighty, it was let down somewhat by an inconsistent gearbox. The damping was exquisite once up to speed, though its resilience made driving around town wearisome - an issue for what was meant to be the most accessible and accommodating AMG. And although there was prodigious grip, the chassis was hardly the most engaging or entertaining, being a little one dimensional in its character.
On the face of it, then, there's room for improvement in this new pair of A45 and CLA45 (the Shooting Brake has been announced already; the GLA will surely follow in time.) The newly developed M139 engine has stolen the headlines - and with good reason, as we'll get to - although the introduction of a new eight-speed dual clutch auto might be just as important to driving fun, promising "fast shifting and optimum connections when shifting up." The new AMG Ride Control suspension is now optionally available from launch, and offers three modes instead of two, in theory broadening the scope for the dampers to provide both comfort and flawless control. And yes, there's the Drift Mode, facilitated by an entirely new rear clutch pack, which should answer those qualms that existed before about a slightly dull drive.
That's the theory, of course, but the A45 would hardly be the first car to impress on paper and then not deliver on the road. There are those concerns about contemporary AMGs perhaps having too much configurability for their own good; the ditching of the bespoke, linear steering rack for a speed-sensitive system and whether a 420hp hatchback can have a great deal of relevance on the road.
Fortunately, however, for Mercedes-AMG, for prospective buyers and for fans of hot hatches in general, the new A45 is, by and large, absolutely superb. Broadly speaking, it bring together all that AMG has learnt since the previous A45 - making turbo engines better than anyone else, as in the E63, incorporating more dynamic tech seamlessly, as in the C63, and making genuinely thrilling track machines in the GT R mould - into one fairly incredible entry point to the range.
That isn't to say there aren't issues that blot the scorecard a little; even in the softest damper setting, there is a concern that the low-speed ride is going to prove pretty firm in the UK. While markedly improved, the dual-clutch gearbox still isn't the sharpest. And while it should be considered a secondary concern, the new A and CLA still aren't the greatest looking cars in the world.
That aside for the moment, the rest of the package is fairly stellar. This entire feature could be dedicated to the engine (handily it already has its own story), such is the manner in which it redefines what to expect from a four-cylinder hot hatch lump. Not simply in the outrageous performance - even if its ability to reach 100mph and beyond is absurd - but in the way it responds to throttle inputs. This sort of specific output couldn't be achieved without some lag, though it's pretty minuscule really, and once up and running the unit is insatiably eager. Even against something like the Porsche 718 flat-fours, the way this M139 zips through to its rev limiter beyond 7,000rpm is remarkable, feeling for all the world like it has hundreds of revs more to give. It makes comparable four-pot turbos, albeit in cheaper cars, feel lifeless and flat-footed, like a wheezy old Ford CVH or similar. There are even some good sounds, too, those provided by the exhaust and its Megane-esque whoosh probably nicer than those from the speakers - though even they are more successful than in most applications.
Furthermore, quibbles with the gearbox only exist because of the standard set by the rest of the car; by and large it's damn good, tactile metal paddles delivering shifts without delay. What lets it down ever so slightly is the occasional reluctance to downshift and automatic calibration that could maybe be improved - it either seems too keen, or too dim-witted. This at launch of the old A45 would have been a revelation; half a dozen years later, such is the pace of development, it merely feels very good. Very, very good.
The chassis, though, is arguably AMG's greatest breakthrough. AMG Torque Control is the key tech, enabled by the rear differential with clutch packs for each rear wheel. Where previously the car could only split up to 50:50 front-to-rear, the new 4Matic+ system is described as 'fully variable.' The AMG Torque Control can then individually apportion torque to each rear wheel, its behaviour dictated by the Dynamic Select drive modes and AMG Dynamics electronics: the more aggressive the mode, the more forcefully it will drive torque to the outside rear wheel to rotate the car on corner exit.
What it means in practise is configurability that really feels its worth. In Comfort mode (but perhaps with the manual gearbox and parpy exhaust buttons pressed), the A45 can play fast and decisive all-wheel drive missile, carving through apexes even more efficiently than before. Here it feels like an A35, to some extent, albeit with a vastly more exciting powertrain: the brakes are superb, the body control excellent (on very smooth tarmac) and the compact dimensions a real boon to making use of a road.
The A45 not only plays that role even better, it also makes use of that sophisticated rear differential to deliver another dimension. Wound up to something like Sport + and with the AMG Dynamics software at Pro (but with the dampers toned down, of course), the A45 has genuine throttle adjustability denied to the car before. Not lurid or wayward, instead just that impression of the rear axle pushing the car around and straightening the wheel out of the corner. The clever diff means there are options basically, the A45 capable enough to carry momentum through bends, and to be a bit silly with different entry speeds, as well as the adjustability that's there in the chassis. It feels great.
The Drift Mode? Not necessary, even if the demonstration given on the launch impressed. From the driver's seat on the road, its shuffling of power between the wheels feel gratuitous and unnatural - much as it does in the mechanically similar Focus RS, actually - not delivering that precise and rewarding drive of the normal modes - or proper rear-drive power slides. Maybe one to investigate further, although there's more than enough to be entertained in how the A45 drives as it is.
On track, the AMG is, if anything, even better. Steering that could perhaps do with a slightly better sense of connection on road feels improved with a load through it (surely aided by new architectural strengthening), the engine hauls tirelessly yet also screams to 7,200rpm and the brakes stay strong despite a longish pedal in 40-degree heat. The chassis shines once more; mobile and direct on corner entry, like a front-wheel drive hot hatch, composed with huge traction through it and with a rear-driven balance on the way out, never wasting a single one of those 421hp. Unless you want it to. Crucially all this happens within limits that would be more than acceptable on a track day, and even makes its driver seem crucial to the process. It's tremendous fun. Even if the gearbox could probably be a bit better.
So good is the A45, in fact, that it's easy to forget there's another car to drive - the CLA saloon. By and large, and entirely unsurprisingly, it's a lot like the A-Class, if not quite as convincing. There are differences that take a back-to-back drive to establish, but the CLA's larger tyres generate more noise and add heft to the steering, and that same feeling of agility isn't quite there. Really close, just not the same. With the best will in the world, the focus seems to have been on making the A45 as good as it can be, then building the CLA from that, which is a fairly crucial difference; it's the derivative, rather than the centre of attention.
Still, it's a great car, a vast improvement on what came before and a better driver's car than the RS3 saloon. By a considerable margin. As for the A45 hatch, on this experience it deserves comparison with the very best cars that £50k can buy. Yes, it's a hatchback - deal with it. On the other hand it's a 420hp AMG, boasting an exceptional drivetrain, clever chassis and enormous desirability. Perhaps the impact will be lessened with direct comparison against rivals, though on this first experience the second generation A45 addresses damn near all the ills of before (ride pending, obviously) while improving what was already very good. Talent, intrigue and character are now all here in no less impressive quantities than in Affalterbach most expensive products. What an achievement.
SPECIFICATION - MERCEDES-AMG A45 S
Engine: 1,991cc, four-cyl turbo
Transmission: 8-speed dual-clutch auto, all-wheel drive
Power (hp): 421@6,750rpm
Torque (lb ft): 369@5,000-5,250rpm
0-62mph: 3.9 seconds (4.0)
Top speed: 168mph
MPG: 34 (34)
CO2: from 189g/km (186)
Price: c. £50,000
(Figures in brackets for CLA; UK CO2 data to be confirmed)