2015 Mercedes-AMG A 45 Renntech 459 Edition

Maybe it’s the comically offensive exhaust. Think reverberant metallic boom, punctuated by a resounding crack on the upshift, and often finished with the cymbal hiss of the dump valve’s release. Or perhaps it’s the styling that – to these eyes at least – has stuck two fingers up at tasteful and gleefully gone on to embrace flamboyancy.

More likely than any of that, it’s the no-prisoners performance served up by the 452bhp, 398lb ft 2.0-litre turbocharged motor.

Regardless of the specifics, the Renntech Mercedes A 45 AMG is an oddly addictive thing.

For £3599, the Nürburgring-based tuners will take your stock A 45 AMG, update its software, put a bigger turbo on that boosts pressure up from 1.85 to 2.05bar and deliver you a car that will do 0-62mph in 3.9sec and strop right on to a faintly ludicrous 186mph. That’s improved from 4.6sec and a limited 155mph in the (hardly faint-hearted) standard A 45 AMG, which produces a mere 355bhp and 332lb ft.

Naturally, Renntech will upgrade the chassis and brakes, too. For £2050 including fitting, you get a set of Pagid brake pads and Bilstein coilovers (tuned and set up by Renntech) in the softer of two available set-ups, catchily titled the ‘Fast Road B16’ package. Opting for the firmer Clubsport set-up, as fitted to our test car, will cost a further £1626. Finally, our car also came with Renntech’s sports exhaust downpipe and catalytic converter, at £1935. At least the trick Dunlop tyres are thrown in for free.

You can opt out of the carbonfibre bonnet and garish decals if you wish, and the £6000 19in forged alloys that our car sits on are also probably an unwise expenditure. 

It’s hard not to look at the Renntech A 45 and immediately expect it to be something that’s way over the top for UK roads, but the creation isn’t as monstrous in practice as it first appears.

The dampers are a particular success. Yes, they’re firm enough that you’ll get lots of short-frequency vertical movement in town or over undulating country roads. More importantly, however, the actual bump absorption and resistance to awkward cambers is effective and sophisticated enough that it keeps the car from skittering over fast mid-corner bumps or jarring uncomfortably over potholes. Stick the seven-speed dual-clutch automatic gearbox in Comfort in order to tame the exhaust and, although tyre and engine noise are still a background hum, the Renntech A 45 is also an acceptable long-distance commuter.

And the engine? The standard AMG take on this 2.0-litre turbocharged motor is pretty remarkable in terms of its outright potency. This has much the same feel, only more, and of just about everything. In particular, it feels much punchier at high revs. Boom past 4500rpm and on to 5000rpm and the Renntech gets a sudden extra surge, keeping up the rate of acceleration with real gusto when the standard A 45 would be spinning into its wheezier realms. Short gearing in the first three ratios also lends a frantic, blink-and-you'll-be-at-the-limiter kind of entertainment to full-bore accelerations, particularly if you spice it up further with the impressively effective launch function.