CAPABLE and quick, the Audi S4 is one of those Q-cars you may not notice - until you drive one.

A lot of attention tends to be focused on Audi's road-burning R8s, its RS selection of saloons or maybe just its sporting TT types, but if you want to be more subtle but still be swift, then the Audi S4 should be on your list to try.

There are saloon or estate derivatives, the later is more expensive, heavier and has a lot more luggage space, while the four-door and five-seater looks more mainstream and unobtrusive.

They share the same powertrain and it's a very highly developed system which packs a punch from start-up to speed limit.

The turbo-charged engine gives almost instantaneous power, rapid acceleration and strong overtaking ability while being able to cruise without strain at the motorway limit in the UK or higher in Germany.

It's built to take high speed and high mileage on motorways, yet the quattro four-wheel-drive also delivers immense grip and taught handling on twisting country roads and mountain passes in mid and north Wales.

The engine is both smooth and quiet even when pressed to perform for overtaking, the changes are seamless and you don't appear to gain much by slipping into manual mode, so well is the system developed. Kick-down is quick and crunches the metres into mini-bites of time.

What the powertrain produces in sophistication and refinement is matched by the steering and brakes. Speed is hauled down simply and quickly with utter control and the wheel imparts immense feedback as well as precision.

All the time the quattro grip keeps you firmly planted on the road and there is near neutral balance on tight turns. It's very safe and very surefooted.

There are a lot of secondary controls to master, thankfully all close to the driver's hands, and they work instantly and easily once you remember what does what as some of the markings are not particularly clear.

Instruments are big and very clear and the driver info settings are excellent once you select a display.

A comprehensive heating and ventilation system is surprisingly easily to use and effective, backed up by powered window. I liked the amount of oddments room as well for the hours you could spend behind the wheel or with a family aboard.

Visibility is excellent all round with very good wipers and washers, bright headlights and reassuring sensors front and back.

Access is good with wide opening doors even into the back seats, shoulder, body and legroom are quite good but not all that generous if you're long legged and in the rear, and the boot has a big capacity but a small opening into it.

The S4 ride is definitely on the firm side but you can adjust from the default setting to either make it softer or harder and that really is useful and transforms the car at the touch of a button.