Road Test: Audi RS5 4.2 FSI Quattro 2dr S Tronic

Who knew? All this time we've been whingeing that our long-term S4 Avant - for all its blend of power and economy - lacked a bit in the way of Good Noise... and it required nothing more than a simple roofectomy.

Because the new S5 Cabrio, armed with the same supercharged 3.0-litre V6 as the S4, sounds most excellent. Roof down, as you pile into a tight corner and flick the left-hand paddle a couple of times, the S5 unleashes an uncouth barrage of coughs and feral snarflings as the DSG drops through the cogs before hurtling you off into the distance with a hard-edged yowl. It's - and here's something you couldn't have said about many Audis a few years back - genuinely entertaining.

Good thing the DSG double-clutch box works so convincingly, for it is your only option: neither a manual nor a traditional automatic transmission is offered.

Happily, you won't be exiting that tight corner with the back wheels of the car pointing in an excitingly different direction to the front wheels. For such a big convertible - the A5 sits on the same platform as the A4 Avant - there's an eerie absence of flex or scuttle shake.

Instead, the S5 feels light and compact, for a couple of good reasons: first, the lightweight fabric roof - like the A5 Cabrio, the S5 does without a tricksy folding hard top - which keeps the centre of gravity low. Second, our test caris equipped with Audi's Quattro Sports Differential, which speeds up the outside rear wheel as you start to lose grip through a corner. At nearly £500, it's not a cheap option, and we'll have to drive an S5 Cab without the diff to see how much difference it makes, but it all adds up to a cabrio that - thougha bit more benign than its most obvious rival, the BMW M3 Convertible - strikes a neat balance of pointiness and ride comfort.

Normally at this point we'd say that if you want a bit more hard-edgedness, you should opt for a fixed-roof, but that doesn't wash here. The S5 Coupe will continue to be sold with the old 4.2-litre naturally aspirated V8 for another year or so, the engine we've never been so keen on in ‘S' guise. Audi says this is because the S5 Coupe is still a new car, which translates as, ‘We didn't want to piss off all our customers who just bought the V8'.

So if you want a two-door and you want the new engine, the convertible it is. But that's no hardship: roof up, it's brilliantly refined, while roof down - well, roof down, it's all about the noise. The best Audi ‘S' yet? It just might be...