Under the bonnet, the A 45 gets a lightly fettled version of the existing turbocharged 2.0-litre four-cylinder petrol engine, featuring mild changes to the induction, combustion and exhaust processes. Power climbs by 21bhp and torque is up by 18lb ft, raising the reserves of the transversely mounted unit to a heady 376bhp at 6000rpm and 350lb ft at 2250rpm.
The flagship of the facelifted A-class line-up also gains a revised seven-speed dual-clutch automatic gearbox with shorter third, fourth, fifth, sixth and seventh gear ratios, along with revised software aimed at shortening shift times.
As before, drive is sent through an electro-hydraulically operated multi-plate clutch four-wheel drive system, which when combined with an optional Dynamic Plus package, includes a mechanical locking differential in place of the electronic locking differential mechanism that continues to come as standard.
Together with the mild changes brought to its driveline, the 2016 model year A 45 also features an optional adaptive damping system in a bid to improve the outgoing model’s ride quality. The new arrangement forms part of a so-called Dynamic Select system that also allows the driver to alter the responsiveness of the steering, gearbox and steering.
What's it like?
The Mercedes-AMG A 45 4Matic has never wanted for sheer speed or dynamic ability, but this upgraded model clearly raises the bar in both departments, making it an even more enticing and accomplished car to drive, whether on public roads or a race track.
The engine remains the undisputed highlight, now feeling even more muscular and determined than before on a pegged throttle in lower gears. Smoother qualities at the lower end of the dial and a more resolute feel through the mid-range also provide the new A 45 with a wonderfully effortless feel when hauling taller ratios at constant cruising speeds.
The 376bhp power peak provides a power-to-weight ratio of 242bhp per tonne – 15bhp per tonne more than its keenest rival, the latest Audi RS3.
Mercedes-AMG claims the sprint to 62mph now takes just 4.2sec, which is a scant 0.1sec inside the time quoted by Audi for the RS3. To put this into perspective, the newly facelifted Porsche 911 Carrera hits the same mark in a claimed 4.6sec.
Significantly, the boost in performance does not come at the detriment of economy, which remains highly impressive. The official combined figure of 42.2mpg is the same as that quoted for the original A 45, endowing it with average CO2 emissions of 161g/km.
Accompanying the increase in raw speed delivered by the upgraded driveline is a noticeable improvement in straight-line stability. With subtle aerodynamic upgrades, including an optional rear wing that comes as part of an AMG aerodynamic package to provide a reduction in lift, the new A45 tracks with enhanced poise all the way to its 155mph top speed. The rear end is now particularly well tied down at higher speeds.
As accomplished as it is in a straight line with its throttle against its stop on a lightly trafficked autobahn, it is the way the A 45 delivers over a challenging back road that really raises eyebrows. Few cars at any price are so swift yet as accommodating from point to point on the road. Its sheer effectiveness, no matter what the weather conditions, places it ahead of many big-name supercars for outright dynamic prowess.