Of all the Renn Sport models that Audi makes, the TT RS perhaps makes the most sense. At its basic level, the Audi TT is a sports car lite. That dropping roof and low-slung stance point to a sporty little coupé or roadster, even when it's a front-wheel drive diesel.

With the 2015 release of the Audi TT, the third-generation model, Audi continued the move towards a more aggressive-looking car. Creases and an evil squint meet more polish and an uplifted interior.

Well, Audi only went and made it into a racing car in the new TT RS. And here it's not only aggressive-looking, it's just downright and wonderfully aggressive.

Where the first-generation TT was about curvy fun, the Audi TT has fought ever since 1998 to throw off the tag of "hairdresser's car". If the new Audi TT is a hairdresser's car, then sign us up at Toni & Guy's academy, because we want in. 

With the regular model a slick road racer, the makeover to arrive at the TT RS isn't as dramatic as it might be. The lines are more or less the same, but with reworking of the front for bigger air intakes, trimmed in matte aluminium colouring, ready to gulp in more air for that pepped-up engine.

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It's the rear oval tailpipes and spoiler that really give the game away. Both the Coupé and the Roadster carry the good looks of the regular car through and give it an RS boost.

We're not looking at the sort of arch widening that once dressed models like the RS4, leaving the TT RS a little more understated. There's even the option to swap that rear wing for an auto-raising alternative, continuing the subtle approach. 

There are some nice details, like the TT badging sitting within the new rear OLED lights. That's right, the TT RS is the first Audi to offer this new lights tech - so expect to see more of that over the next year.

Overall, the TT RS is a makeover that you could almost miss. Well, until you thumb that steering-wheel mounted start button and hear it roar and splutter.

This understated nature flows through into one of our favourite options: control of the exhaust noise. When equipped with the RS sport exhaust system, you have the option to control the TT's exhaust flaps to release the throaty, guttural roar of the engine, or silence it. With the noise button on, you certainly won't miss a thing.

There's no artificial boosting here, it's all natural, you just have a button that will switch between quiet and noisy by moving a flap in the exhaust. As we said of the Audi R8, the thing that really defines what Audi is doing with its performance models is giving you ridiculous power, but paired with control and practicality.

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Being able to turn off that engine noise (something you can't do in the RS3, for example) means your neighbours won't have to hate you (although they might be jealous, because you own one). But when you hit one of those tunnels skirting the shoreline of Lake Garda, the TT RS can roar like a supercar and you can bask in the magnificence of the noise from the 5-cylinder engine. 

With engineering in mind, the Audi TT RS has a new engine that's been on a diet. Sticking to five cylinders, Audi walked through a number of steps to shed weight and increase power. The engine block is now aluminium rather than iron, the cam shaft is stronger but lighter, the sump is a much lighter magnesium alloy and the turbo has been reconfigured, to make it more compact and more efficient.

The result is more power and greater efficiency, a better engine all round, and less weight at the front, to improve the handling.

Pairing this new 2.5-litre, 400bhp petrol engine with Audi's Quattro all-wheel drive, routed through a 7-speed S tronic gearbox, you're looking at a TT that races to 62mph in 3.7-seconds for the hard top Coupé, or 3.9-seconds for the soft top Roadster. The 480nm torque is delivered across a huge band of revs too, so there's power, power and more power - and right from the off.

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Not wanting to be a sports car that talks the talk and fails to walk the walk, the TT RS offers launch control (just as you'll find in the Audi RS3 and the likes of Porsche 911 Turbo S). Switching over to Sports mode, there's a special mode of the ESP (the traction control system) designed for racing. You simply have to put your foot on the brake and floor the accelerator and the engine will leap to, and lock at, 3,500 revs. Release the brake and it's like being fired from a cannon. 

So this might clash with what we've been saying about practicality, but if you're after a performance TT, you want some of the fun stuff too. When you'll actually get to use it, we're not so sure, but you can say the same of the Ford Focus RS's drift mode, or the Mustang's line lock

Like the Audi R8, the TT RS offers you huge performance, but holds your hand, keeping you heading in the right direction, with a feeling of competence. This isn't a car that's so powerful it's scary; it's not a brute, it's not unruly.

For some that might be the downside. The TT RS is about precision and getting you where you're going, rather than slithering and sliding. Purists will point out that this isn't a mid-engine rear-wheel drive sports car like some of its close rivals, but Audi will point to its performance figures and smirk, perhaps reminding you that you'll be going forwards, rather than sideways.

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Offering a little more assistance and to help control the body roll of those sitting within, the sports seats also offer powered side adjusts, so your lithe body is gripped, or your expanded girth accommodated, resulting in a seat that's really comfortable, in an interior that's plush and, like the original car, centred around the driver. That means the passenger gets to look at an empty piece of dash or out the window, rather than doing anything useful like fiddling with the music.

Unlike some of the other RS models - the RS Q3, or the RS6 Avant, for example - the TT RS feels much more like a car designed to race. It has the stance and the poise meaning that on the track it's a blast; squirming as you brake hard, keeping you on the line, gripping through the corners, and exploding with power as you come out and hit the straights. 

There are options for those who want more: there's the RS sports exhaust that we've mentioned, but there's also a carbon ceramic brake option. The sports suspension is standard, but there's an option for adaptive dampers with magnetic ride control. There is no manual gearbox option, however, so it's a case of taking Audi's autobox and liking it - but manual paddle control is also offered, which might help you avoid the occasional pause in power when the revs drop low (not that this happens in Sports mode).

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These different aspects of the car's drive systems are pulled together in the drive select modes, so when you're in Dynamic, you're really in dynamic and set to hit the track, skipping through gears and keeping the revs high, popping and booming with orchestral majesty when you hit the brakes hard. The sound is very much part of the thrill and everything comes together with precision once you're in the driving seat.

Flipping to Comfort mode and the engine noise drops, the gear change is regular enough to keep things quiet and the throttle response is just the way you'd want it for popping to the supermarket to buy some curly kale. 

You might be sitting in a track-happy thoroughbred, but the TT RS is as useful on a Sunday drive as it is midnight street racing. The suspension is naturally firm, keeping the car flat through fast corners, but forgiving enough to not cave in your posterior when you hit a speed bump a little faster than you should.

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The TT RS Coupé sees a 2+2 configuration with the suggestion of a backseat. Just as you'll find in the rear of something like, say, a Porsche 911, there's a rear seat that's better suited to your coat or bag than it is a childseat or your dog (ok, it's probably perfect for your dog). You can fold an adult into that space behind the front seats, but with the move to racing seats, there's a little less space than you get in the regular model. Perhaps a BMW M2 would suit your needs better, if backseats are really a point of focus.

For the Audi TT RS Roadster, the rear seats are lost so that the cloth roof can be accommodated, so it's a two seater like, say, a Porsche 718 Boxster. The Audi does feel more modern with its Virtual Cockpit display, keeping the centre console clear of other displays, while still offering support for things like Android Auto and Apple CarPlay alongside Audi's great entertainment options - just as you'll find in the regular Audi TT. 

Audi will also be offering a smartphone app to owners, meaning you'll be able to track your stats from your phone, check your lap times and everything else.

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There are plenty of options for giving the interior a lift, too: from colour trim to carbonfibre door handles, engine covers and centre console tops. We have to say this carbon treatment gives a really good finish to the TT RS, although we're sure it will cost you a pretty penny on a car that's already pretty expensive.

The TT RS Roadster launches alongside the Coupé, meaning you get the option of soft or hard tops and, having driven both, it's the Coupé that has the edge on performance for us. We also think it's slightly better looking with that rear roofline. For those wanting the wind in their hair - and roof down driving is one of the best things about having a sports car - then the Roadster offers much the same set of driving thrills.

The drawback of the Roadster is the level of compromise you make for that roof in a car that's already compact: you lose those back seats and the boot is smaller, as is the opening, so managing luggage is slightly less convenient. If it's pure practicality, it's the Coupé that wins. If your other car is a Volvo XC90, go with the Roadster.

Verdict

The Audi TT takes a compact and sporty car and makes into a ridiculously fun racer, fit for all conditions. It punches right into the middle of the Porsche pack, doing what Audi does so often: engineering itself to better performance and, as it is, pricing itself into the middle of the Porsche pack.

Of all the RS models, we can't help thinking that the TT RS makes the most sense. It's the car that feels the most natural with this enhanced power and performance, in a way that an SUV doesn't. At the same time, will Audi be able to shake off that old image of the TT of old? Will prospective Porsche buyers consider a car that's quite similar on the surface, even if the skin beneath delivers a very different setup? That's perhaps the TT RS's biggest barrier. 

Like all Audi RS models, the TT is expensive. Something it justifies with impressive performance figures and a high level of trim. But starting just north of £50,000 there are some really tough choices to be made about what you're actually looking for in a compact sports car.

The bottom line is that Audi has taken everything we love about the TT, kept every ounce of practicality, and made it into a monster; a beautiful monster at that.