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Fast, frantic but perfectly practical, the Audi RS 4 remained the market's definitive mid-sized high performance estate in this post-2018-era guise. The B9-series version of this Ferrari for families swapped its old V8 for a 2.9-litre V6 and an even more sophisticated quattro 4WD system that set this model apart in its unique little niche. Like the previous B8-era RS 4, this one could hit 174mph on the Nurburgring but was just as happy collecting your dry cleaning. You only truly get a sense of just how fast it is by following behind in something else. At which point, whatever that might be, it'll be hard not to wish you were in an RS 4. This car, you see, is one of a kind.
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Performance Sporting Cars
History
Every once in a while, a car is developed that is so good and such a class benchmark that other manufacturers are very wary about taking it on. The Range Rover for example - maybe even the Mazda MX-5. The first two decades of this century, Audi made such a car too - and it was this one, the RS 4 Avant. We're going to look at the B9-series model, launched at the end of 2017.
At its 2018 UK launch, for those who wanted a very, very fast, four-wheel drive mid-sized estate with supercar performance, there was really no precisely comparable rival to this model. The work of Audi Sport, the Ingolstadt brand's go-faster arm, the genes of the RS 4 could be traced right back to that performance division's very first product, the RS 2 estate that was co-developed with Porsche back in 1994. It paved the way for the first generation in the RS 4 line, the 2.7-litre twin-turbo V6 model of 2000, ferociously quick but ultimately rather unsatisfying - in the way that very fast Audis used to be.
The second generation B7-series RS4 of 2006 was a turning point in that regard and proved to be a landmark contender for the brand, a machine satisfying enough at last to properly challenge the all-conquering BMW M3. It made good use of the charismatic 4.2-litre V8 first used in Audi's R8 supercar - as did the replacement B8-series RS 4 model of 2012. For this fourth generation B9-series model though, that classic powerplant made way for a smaller but punchier 2.9-litre twin turbo V6 that managed to be 25% more efficient, but every bit as quick.
Like that original RS 2 model, this one was developed with Porsche. The 450PS power output might have been the same as the previous B8-series design but there was masses more pulling power through the ratios of this replacement model's much more responsive auto transmission, an 8-speed Tiptronic paddleshift set-up. In addition, Audi's traditional advantage over similarly-performing mid-sized models like the Mercedes-AMG C 63 and the BMW M3 - its quattro 4WD system - was retained and improved for the B9, which also gained an all-new stiffer, lighter MLB platform. Plus a standard rear Sport differential to further help get the torque to the tarmac through the turns. There was a mid-term update for the RS 4 in 2020 and various short-run special edition models followed that. Audi launched a 'Competition' handling package for the car in 2022, which increased top speed to 180mph. Finally, there was an 'Anniversary edition' launched in 2024, which boosted total output to 470PS. RS 4 production finished in 2024.
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What you get
The exterior design of the RS 4 has always been about blending just the right amount of discretion and purpose. It's the sort of car that gets a nod of appreciation from those who know what it is, but is low key enough to pass unnoticed most of the time. Under the skin is Audi's MLB platform, the same one which underpinned the RS 5 coupe and Sportback models that shared this car's 2.9-litre V6 TFSI twin turbo engine. Appropriately, aesthetic inspiration came from a competition model, Audi's 90 quattro IMSA GTO racer, hence the blistered wheelarches, the lacerated air intakes and the huge oval exhaust pipes. The 2020 facelift added a more aggressive front end with a 'frameless' black honeycomb grille, a revised bumper and front splitter, plus flared wheel arches.
Up front, you'll find yourself in a cabin that we think will really sell you this car, incorporating as it does plenty of elements designed to set this RS 4 model apart from humbler A4 variants. This flat-bottomed RS sport leather steering wheel is of course bespoke. So are the stainless steel pedals. We really like the seats. They're anatomically-shaped and electrically adjustable, plus they incorporate a standard massage function and are perfectly positioned in front of a wheel through which you view the all-digital Audi 'Virtual Cockpit'.
You may be familiar with this set-up from some of the brand's other models made in this period. Here, it was standard, a 12.3-inch LCD colour monitor that replaced the usual instrument binnacle dials with a layout that was fully digital and customisable, using smart 3D graphics and highly detailed effects. Anything the 'Virtual Cockpit' set-up can't tell you will almost certainly be covered by the slimline MMI infotainment display that dominates the top of the dashboard. Appropriately, this flagship model includes Audi's top 'MMI Navigation Plus with MMI touch' package with its 8.3-inch monitor featuring crisp 3D maps and responsive Nvidia graphics. This monitor increased in size to 10.1-inches, as part of the 2020 facelift.
In the rear, a previous B8 RS 4 owner would notice the benefit of the extra 12mm of wheelbase length this fourth generation B9-series model enjoys over its predecessor. Audi claimed that there's 23mm more legroom back here than there was before. Raising the rear hatch reveals that this B9-series RS 4 model's extra 26mm of length freed up 15-litres more boot space than was offered by its predecessor, the total rising to a class-leading 505-litre figure.
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What to look for
We've heard of stuck thermostats, random idle speeds at start-up and engines that struggle to start from cold. Some owners have reported faulty cam sensors. And in a few cases, the carbon fibre engine cover has become detached. Some owners experienced gearbox oil leaks, which were fixed under warranty. And a few owners reported difficulty in restarting their RS 4 models in the morning after an overnight stop, which they ended up fixing by stamping harder on the brake pedal to get the sensor talking to the ECU. There have been issues with failing DRC actuators, which is usually signalled by a knocking noise. And the brakes have a reputation for squealing. There have been reports of leaking headlight covers. And electrical glitches that affect the side assist, exit warning and automatic headlight operations.
The other issues with this B9-era RS 4 relate to carbon build-up on the intake valves, potential rocker arm failures and occasional issues with things like exhaust rattles and engine misfires. Steer well clear of any cars that have been tuned because that can exacerbate some of the engine issues, particularly those related to the rocker arms. And check the service record extremely carefully because regular maintenance can address the intake valve carbon build-up issue, which can be alleviated by adequate regular lubrication.
We've heard of gearbox problems, seat backrest faults and suspension issues, so check all these on your test drive. The steering rack can experience electrical and mechanical failure and might be noisy too. The most reported faults related to interior trim and non-engine electricals. Look out for bodywork scrapes and kerb damage to the large alloys. There were a few issues with the car's infotainment system, with phones not connecting properly and flickering screens being the main problem. Buzzing interior trims were also reported. The automatic gearbox should be checked to make sure it's had a regular oil and filter change, as should the quattro four-wheel-drive system.
Many RS 4s will have been company or lease cars and, as a result, you should check the condition of the bodywork carefully. The high-quality fit and finish of an RS 4 also makes it an ideal candidate for clocking, so ensure the history is absolutely verified.
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Replacement parts
(approx based on an RS 4 Avant 2018 2.9 TFSI - Ex Vat - autodoc.co.uk) An oil filter costs in the £10-£23 bracket. An air filter's in the £16-£40 bracket. Front brake pads sit in the £26 to £94 bracket for a set; for a rear set, it's around £20-£43. Front brake discs sit in the £41-£78 bracket; for a rear pair, you're looking at around £17-£100. Radiator prices vary widely - from £125-£368, depending on brand. As do costs for a thermostat (anywhere in the £43-£70 bracket we found).
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On the road
Not a lot prepares you for just how quick this car really is. To be specific, rest to 62mph here occupies just 4.1s, which is 0.6s quicker than the previous generation model and also a fraction quicker than you'll go in this model's closest rival from this period, the Mercedes-AMG C 63 Estate. As usual with fast Audis, the maximum speed is rather pointlessly capped at 155mph, though it was possible for original buyers to pay Ingolstadt an obscene amount of money to get the restrictor lifted, in which case your RS 4 will top out at nearly 180mph (which was the top speed of the post-'22-plate 'Competition' versions). The creamy, rather digitalised engine soundtrack you get as the revs rise from this fourth generation RS 4's 450PS 2.9-litre V6 isn't a match for that of the previous model's 4.2-litre V8. After a while though, you rather warm to the way that this Porsche-developed powerplant snarls purposefully on up-shifts and lets out little pops and bangs as you snick the steering wheel paddle shifters down through the closely-stacked ratios of the 8-speed Tiptronic gearbox. It was uprated to 470PS in the final 2024 'Anniversary edition' model.
This RS 4 also tackles the turns more effectively in this B9 form. Part of that is down to a re-developed quattro system which usually directs 60% of torque to the back wheels but, if conditions demand, can send up to 85% of power to the back or, if necessary, as much as 70% to the front. The set-up was designed to work with a torque vectoring system that applies minimal brake interventions to the wheels on the inside of any given curve before they start to spin, maximising traction and making handling more precise, agile and stable. Also playing its part here is the standard-fit 'sport differential' which at speed through tight corners can constantly vary the amount of torque distributed to each of the rear wheels. As usual with Audis, there's a 'drive select' driving modes system enabling you to tweak steering, throttle response, stability control thresholds and the impact of that 'sport differential' system. It'll also alter suspension feel if you've got a car whose original owner paid extra for adaptive damping.
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Overall
Never mind the R8 supercar or the TT coupe, if you want to understand how brilliant Audi can be in building a sporting car, the RS 4 has long been the best barometer. Was it still in this fourth generation B9-series guise? In some ways, yes. Like many, we miss the previous B8 model's high-revving 4.2-litre V8, but there's little doubt that the replacement V6 Porsche powerplant - though less aurally emotive - has more real world punch. Which seems appropriate in such a resolutely real world performance car.
Drive it and you'll experience a slightly guilty thrill as if something this much fun really couldn't be legal. One day cars like this might well be legislated out of existence. In the meantime, enjoy this one while you can.
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