Used BMW 3 Series review: 2012-2018 (Mk6)
Attractively styled and a delight to drive, the BMW 3 Series Mk6 is one of the best used compact executive cars you can buy
The original BMW 3 Series created the genre of the compact executive car and over several generations the model has become the benchmark against which all its rivals are judged. Whether or not you’re a car enthusiast you’ll appreciate how fantastically well the 3 Series Mk6 drives, while its cabin design, materials and equipment levels create an ambience of contemporary sophistication. These qualities unite with sharp, modern exterior styling to form one of the most aspirational cars on the market.
Although the 3 Series Mk6 is also available as an estate car called the Touring, a five-door hatchback called the Gran Turismo and the high performance M3, here we’re dealing solely with the mainstream versions of the four-door saloon. We’ve covered the others separately and you can view their reviews by clicking on the links.
Launched in the UK in early 2012 and discontinued late 2018, the 3 Series Mk6 – which you may also see referred to by its BMW codename, F30 – features a broad range of turbocharged petrol and diesel engines, as well as a couple of petrol-electric hybrid powerplants. The diesels especially are extremely efficient, combining strong performance with excellent fuel economy and low emissions.
In fact, the 3 Series Mk6’s diesel and petrol engines are so efficient that they largely render the range’s hybrid models redundant, although the ability of the petrol-electric plug-in hybrid 330e to run for up to 25 miles solely on electric power holds wide appeal.
Refinement is another key element of the 3 Series Mk6’s success: its engines are smooth and sweet-sounding, and the cabin little ruffled by wind and tyre noise. The caveat here concerns the M Sport versions; their lowered, stiffer suspension and 18-inch diameter alloy wheels with low-profile tyres disturb the cabin’s serenity by crashing and banging over rough road surfaces.
The 3 Series Mk6’s regular suspension is a joy, though, striking an excellent balance between ride comfort and the firmness necessary to make the car zip neatly around corners. Precise steering adds to the high quality of the driving experience. A six-speed manual gearbox is standard, but if your budget stretches to the eight-speed automatic then opt for it – the gearshifts are quick, silky, and perfectly match how you’re driving, whether that be pottering around town or cruising along an empty back road.
Space inside the 3 Series Mk6 is on a par with that of rivals such as the Audi A4 and Mercedes C-Class, which is to say that it’s roomy up front and potentially a little tight in the back if a six-feet-tall rear passenger is sitting behind a similar-height driver. There’s enough elbow room in the rear for three as long as you’re not going far. Luggage space is adequate for this size of saloon, but the shape of the boot opening can restrict access – some models have a split-folding rear seat that improves practicality.
BMW doesn’t make as big a deal about its cars’ safety as, say, Volvo does, but the 3 Series Mk6 performed exceptionally well in its Euro NCAP crash tests, gaining a full five-star safety rating with a very high overall score.
What’s the history of the BMW 3 Series Mk6?
The BMW 3 Series Mk6 first arrived in UK showrooms in February 2012 and was available with an impressive range of refined and efficient turbocharged petrol and diesel engines: the latter were immediately the most popular choice because of their excellent fuel economy and the tax advantages they afforded company car drivers.
BMW introduced the ActiveHybrid 3 Series in mid-2012. This mild-hybrid version of the 3 Series Mk6 combined a turbocharged 3.0-litre petrol engine with a small electric motor to create a high-performance derivative that could also be driven up 2.4 miles using solely electric power. Shortly afterwards an entry-level 1.6-litre petrol engine was launched.
The basic trim grade hierarchy for the 3 Series Mk6 started with the ES and rose through SE, Sport and M Sport, although not all the grades were available with all the engines. There were also a couple of trim packs – Modern and Luxury – that added a few extra goodies to what was already available on the SE, while in mid-2013 the Business grade was offered on the fuel economy-focused 320i and 320d EfficientDynamics models. Aimed at company car drivers, Business trim comprised plush leather upholstery, heated front seats and the BMW Business Media Package.
In May 2015 the 3 Series Mk3 underwent a revamp. Its styling was subtly enhanced, the quality of the cabin materials was improved, sat-nav became standard on all models, and the engines were revised to further improve their efficiency. Notable additions to the engine range were a turbocharged three-cylinder petrol badged as the 318i (it replaced the 1.6 four-cylinder), and the petrol-electric plug-in hybrid 330e, which could travel up to 25 miles in all-electric mode, introduced in February 2016.
The 3 Series Mk6 was discontinued in late 2018 to make way for the seventh-generation model that made its UK debut in March 2019.
Which is the best BMW 3 Series Mk6?
There aren’t many poor engine choices from the 3 Series Mk6 line-up: petrol or diesel, most engines are refined, quick and economical, but there are a few to be avoided. While the 114bhp 1.6-litre turbocharged diesel in the 316d gives up to 63mpg, it feels underpowered in the 3 Series Mk6. And despite posting some respectable on-paper performance figures (0-62mph in 8.9 seconds, for example), the 136bhp 1.6-litre petrol engine in the 316i also seems out of its depth in a car of this size and weight.
The ActiveHybrid 3, on the other hand, has no problem delivering suitable performance, it just doesn’t seem to have much relevance as a used car purchase. Its 3.0-litre petrol engine and small electric motor combined give a power output of 335bhp, but the ActiveHybrid 3 can only travel up to 2.4 miles at a maximum speed of 37mph purely in electric mode, while its 47.9mpg Combined fuel consumption and 139g/km emissions figures are easily eclipsed by those of several of the diesels.
The 320d EfficientDynamics is one of the better diesel models. Powered by a 161bhp 2.0-litre turbodiesel, it features a package of measures that focus on optimising its fuel economy and reducing its CO2 emissions – these include slipperier aerodynamics, low rolling-resistant tyres mounted on narrow wheels, economy-biased ratios in its gearbox, and changes to its engine management system. The 320d EfficientDynamics is capable of up to 74.3mpg, and some versions just sneak below 100g/km for CO2 emissions, although most produce 102g/km. Bear in mind that these figures were achieved on the old NEDC emissions test, and will be hard to replicate in real driving. Despite its parsimony, this model still has decent performance – 0-62mph in 7.9 seconds.
The regular 320d is a great alternative. It’s slightly quicker yet is still able to squeeze 67.3 miles from a gallon of diesel, while its emissions are a respectable 111g/km. If you prefer to drive a petrol engine then check out the 320i EfficientDynamics, which at 53.3mpg is the most economical of the unleaded drinkers in the 3 Series Mk6’s engine range.
If you’re looking for a little more performance, then the diesel-engined 330d should satisfy. Its 254bhp 3.0-litre six-cylinder turbodiesel can rush it from standstill to 62mph in 5.6 seconds, while it’s also able to deliver up to 56.5mpg.
And if you can afford it, buy a 3 Series Mk6 with BMW’s outstanding eight-speed automatic gearbox. Not only does it make everyday driving easier, especially in traffic, but for most people it’s also more economical than using the six-speed manual gearbox.
As for trim grades, the SE has everything you need, if not everything you might want. Its specification includes dual-zone climate control, front and rear parking sensors, automatic lights and wipers, keyless central locking and starting, an infotainment system, alloy wheels and cruise control. If you find a post-2015 facelift version then there’s also sat-nav, smartphone connectivity and LED headlights.
It's very easy to be tempted by an M Sport model – its aerodynamic body kit looks great, as do its 18-inch alloys wheels. Its sports seats and Dakota leather upholstery are also alluring. But two things to bear in mind: the M Sport’s hard suspension isn’t to everyone’s taste, and used examples hold their value extremely well.
What are the alternatives?
For many years there have been only two important rivals to the BMW 3 Series – the Audi A4 and Mercedes C-Class, but during the lifespan of the 3 Series Mk6 the Jaguar XE also entered the picture, as did the Alfa Romeo Giulia, both of which are good to drive and have a bit of pizzazz about them.
Running costs, MPG, CO2 emissions and insurance
Economical petrol and diesel engines take some of the sting out of daily running costs and road tax, but insurance prices can be steep
While the high-performance petrol versions of the 3 Series Mk6 – the 330i, 335i and 340i – have fuel consumption figures in the 30s and mid-40s MPG, even the most powerful of the diesels will give you more than 50mpg, with the rest returning up to 74mpg. And with good fuel economy comes low CO2 emissions, which is important for the 3 Series Mk2 because the road tax (VED) for cars registered before 1 April 2017 is determined by their CO2 output.
When the 3 Series Mk6 was new, BMW offered a five-year fixed-price servicing package, so if you’re looking at a very late example there’s a chance that the balance of that package remains. Otherwise, service intervals are every two years or 15,000 miles, whichever comes first, with a minor service for a four-cylinder diesel costing around £250, and a more intensive service for a six-cylinder petrol engine upwards of £550. If your 3 Series Mk6 is now outside of BMW’s three-year warranty it’s worth shopping around for servicing – BMW is such a popular marque that there are plenty of good quality specialists charging for less than an official dealer.
How much do BMW 3 Series Mk6s cost?
The 3 Series Mk6 was an extremely popular company car when new and consequently there’s plenty of choice on secondhand car dealers’ forecourts. Because so many started life as company cars it’s no surprise to find a wealth of high-mileage examples, especially among the early models from 2012-2015.
Dealers tend to make the most of the cachet connected to the BMW badge, asking as much as £6,000 for a 2013 316d SE with 115,000 miles on the clock. Sub-£10,000 cars generally have high mileages and the less powerful engines from the range, although you may find keener pricing among private sales.
There’s plenty of variety in terms of trim grades and mileage if you have between £10,000 and £20,000 to spend, but low-mileage models from 2017 and 2018 can be in the high £20ks. Low mileage has an impact on prices no matter what the age of the car, as do Sport and M Sport trim grades, and cars fitted with BMW’s xDrive four-wheel-drive system.
With so many engine options to choose from over the 3 Series Mk6’s comparatively long lifespan, it’s best to check on our sister site, Buyacar, for the very latest pricing information.
What’s it like for fuel economy, emissions and tax?
If you were to believe the official fuel consumption figures, the petrol-electric plug-in hybrid 330e is the economy star of the 3 Series Mk6 range, with a combined figure of 148.7mpg. That is, however, an anomaly of the official testing procedure. It assumes that the hybrid’s batteries are always fully-charged and that every trip you make will allow you to exploit the full electric-only range of 25 miles. For most owners, most of the time, fuel economy will be substantially less than that of the diesel 3 Series Mk6 models.
Of the diesels the 320d EfficientDynamics Plus is the economy king. Its combined consumption figure is 74.3mpg, while the non-Plus version’s is 72.4mpg: impressive stuff. Most of the other diesels are also easy on your wallet, with the 316d, 318d and 320d all returning around 68mpg. The high-performance 330d and 335d models give 56.5mpg and 51.4mpg respectively, respectable figures given how quick they are.
The 335i and 340i six-cylinder petrol-engined models perform well against the stopwatch but not at the fuel pumps, both achieving around 35mpg – the four-cylinder petrol models (316i, 318i, 320i, 328i, 330i) deliver mid to high-40mpg.
For the lowest annual road tax look towards the diesels and the petrol-electric plug-in hybrid models, because they have the better CO2 emissions. This especially makes a difference if the 3 Series Mk6 you’re considering was first registered before 1 April 2017 – tax rates for these cars are based on their CO2 output. Low emissions models such as some versions of the 316d can cost as little as £20 to £30 to tax, and some versions of the plug-in hybrid 330e don’t cost anything at all. On the other hand, a petrol-engined 320i with higher emissions will land you with an annual bill of £210.
Cars registered after 1 April 2017 mostly attract flat-rate road tax of £155. There are some exceptions, however. If the 3 Series Mk6 you’re looking at cost in excess of £40,000 when new, it’s also subject to a luxury car surcharge, taking the tax bill to nearly £500 annually. So when buying, check the tax situation with the vendor.
How much will the BMW 3 Series Mk6 cost to insure?
The 3 Series Mk6 is a prestige car, some versions of which are very high performance, and the insurance industry treats the BMW accordingly. Insurance groups range from 18 to 43 out of 50.
Reliability and common problems
You might expect a BMW to be a paragon of reliability, but in the case of the 3 Series Mk6 you’d be wrong
A string of recalls and a plethora of other problems with the 3 Series Mk6 demonstrate that even the best names in the business don’t always get it right when it comes to reliability. Some issues are the petty niggles you’ll find on any car, no matter who makes it, but others are more serious with potential safety implications.
By now BMW recalls should have remedied the 3 Series Mk6’s more critical afflictions, but it’s always best to check that repairs have actually taken place – an official BMW dealer should be able to help here, if you furnish them with the car’s registration details and Vehicle Identification Number, or VIN, which can be found on the V5 registration document.
Are there any common problems and things to look at?
We’ll deal with the 3 Series Mk6’s recalls in a moment, but there are other things to watch – and listen – out for. A metallic rattle from diesel engines in models produced before 2015 can be indicative of a failing plastic tensioner for the timing chain: if left it can lead to very expensive engine damage. A few early versions of the petrol 320i and 328i suffered with this problem, too.
The VANOS variable valve timing system on early six-cylinder petrol engines can suffer from blocked oil pipes and oil leaks which are costly to remedy, while on the 320i there are reports of the oil pump gears shedding shards of metal that are ingested by the engine and can cause engine failure.
Part of the charging system for the petrol-electric plug-in hybrid 330e is known to malfunction, although affected cars should have been identified by this stage and replacement components fitted – do check, though, because this is expensive to fix. And on the subject of electricals, be sure to test that every electrical item in the car works as it should, because any gremlins will be tricky and costly to sort out.
Clutch components on early 3 Series Mk6s equipped with a manual gearbox are likely to be reaching the end of their natural life and causing notchy gearchanges and juddering through the transmission, while random models have an excessive appetite for front brake discs and pads.
Older examples of the 3 Series Mk6 are now likely to suffer age-related creaks and rattles, while a clattering from the rear suspension of cars fitted with optional electronically controlled dampers is annoying but not a sign of anything to be unduly concerned about.
In the hands of solo-travelling company car drivers, some 3 Series Mk6s could amass high mileage while still looking pretty tidy inside. Unscrupulous car dealers have been known to use that fact to their advantage, electronically winding back the mileage on a good condition 3 Series Mk6 in order to make more money from it. On cars older than three years you’ll be able to check the mileage on old MOT records, while an official BMW dealer will be able to consult service records to see if the mileage seems genuine.
What about recalls?
The 3 Series Mk6 has been subject to numerous recalls, but not for all examples for all of the recalls. While our list will give you a general idea about which cars are affected by what, take a note of the VIN (Vehicle Identification Number) of the car you’re interested in – which you’ll find on the V5C registration document – and ask a BMW dealer to tell you what work has been done.
Cars made up until 8 December 2015 were recalled for a potential fault with the power steering, while cars built between 1 September 2014 and 31 March 2015 needed to have the driver’s seatbelt mechanism checked and possibly replaced.
Loose bolts on the manual gearbox of cars produced between 1 February and 30 June 2013 could make it hard to change gears, and a dodgy fuel pump on cars made between 1 September 2013 and 30 April 2014 could cause the engine to stall.
A leaking cooler on the EGR (exhaust gas recirculation) system of diesel engines made from 19 September 2015 until 22 November 2017 could affect power output, as could a faulty crankshaft sensor on some engines built between 16 May 2018 to 7 June 2018. Of greater consequence was the fact that a crucial engine bearing might not have been properly inserted on cars produced between 11 March and 9 July 2019 – affected models needed a new engine.
Although it was extremely unlikely that many – if any – 3 Series Mk6 owners would ever suffer this problem, BMW recalled cars built between 1 January 2015 and 31 March 2016 to replace the rear axle bolts. Incorrect ‘one-use’ bolts had been fitted, and if the rear axle were to be removed and the bolts re-used, they might fail.
What do owners think?
In our 2018 Driver Power owner satisfaction survey the 3 Series Mk6 placed 39th out of 75 cars, despite all the recalls, suggesting both that owners are a forgiving bunch and that the car’s other qualities outweighed any disappointment over reliability.
BMW as a brand didn’t do so well in the same survey, ranking a lowly 21st out of 26 manufacturers.
Engines, drive and performance
Powerful and economical diesel engines, together with superb driving characteristics, cement the 3 Series Mk6’s position as a class-leader
Even if you’re not particularly interested in cars, the 3 Series Mk6’s driving experience will make an impression on you. The smoothness and power of the engines. The quietness inside the cabin. The way that when you drive through a series of corners the steering reacts quickly and precisely, and the suspension behaves in a measured, controlled fashion.
Press the accelerator pedal and there’s an immediate yet progressive response. Apply the brakes and there’s no delay to the car slowing down, and nor do the brakes snatch. Need to stop or go with greater haste? The 3 Series Mk6 delivers in a manner that can be startling in its intensity in the higher performance versions, but still makes the driver feel as though they are in full control.
That said, models fitted with the M Sport suspension aren’t to everyone’s taste. Lower and stiffer than for other 3 Series Mk6s, the M Sport suspension’s ride quality on coarse road surfaces can inflexible and crashy – some people find it unacceptably harsh, others are prepared to put up with the thumping and bumping in exchange for the extra sportiness it brings. M Sport versions of the 3 Series Mk6 are undeniably good-looking, but go for an extended test drive to ensure that you really can live with that compromised ride quality: if you’re lucky you might find an M Sport fitted with optional electronically controlled dampers which reduce that compromise.
Which engine should I choose?
You can’t go wrong with the 187bhp turbocharged 2.0-litre diesel engine found in the 320d, and it’s the model you’re most likely to find on a used car forecourt. It has an abundance of the real-world pulling power that makes overtaking a doddle and motorway trips relaxing, it’s refined and quiet, and when driven with restraint can deliver up to 67mpg. The 320d EfficientDynamics is even more economical but doesn’t feel quite as energetic as the regular 320d – the lower-powered diesels also lack its urge and its frugality.
The high-powered turbodiesel models, the 330d and 335d, are exceptionally fast, the latter being the quickest of all the 3 Series Mk6 derivatives. On paper the petrol-engined 340i will outsprint the 330d – 0-62mph in 5.2 seconds compared with 5.6 seconds – but in reality the turbodiesel’s crushing and easily accessed pulling power at low engine revs gives it the clear performance advantage: the same is true of the 335d, even more so. The undoing of these high performance diesel models is their thirst – 51.4mpg and 56.5mpg respectively – but that’s still comparatively acceptable.
If BMW didn’t make such excellent diesel engines then the 3 Series Mk6’s petrol units might be worthy of recommendation. They’re smooth, refined and economical for their type, but their performance against the clock is little better than that of their diesel siblings and inferior in real-world driving; they’re nowhere near as economical, either.
Interior comfort and safety
With adequate room inside for four adults and high levels of refinement, the 3 Series Mk6 is a stylish and relaxing way to travel
While cars from the compact executive class typically aren’t cavernous inside – their original audience was the company car driver, mostly travelling solo – the 3 Series Mk6 will seat four adults comfortably, with the proviso that they’re less than six feet tall. Rear seat passengers will find knee and headroom adequate rather than generous, and for short trips you can squeeze a third occupant into the back.
The 3 Series Mk6’s cabin is well insulated from tyre and wind noise, while the fact that you don’t have to work the diesel engines hard to achieve brisk performance adds to the overall sense of serenity and comfort.
Boot space is average for this type of car, but sufficiently large that it will accommodate the baggage requirements for all four occupants for a weekend away. Some models feature a split-folding rear seat to allow you to transport longer items, but because this was an optional extra you may struggle to find a car with this feature.
What’s the BMW 3 Series Mk6 like inside?
There’s a restraint to the 3 Series Mk6’s cabin design that’s born out of BMW’s long-standing commitment to simple ergonomics – it’s not the most stylish or contemporary-looking interior within its peer group, but there’s a simplicity and logic to the positioning of the main controls that makes it easy to feel at home behind the wheel.
The only element that jars visually is the colour screen for the infotainment system that perches on top of the dashboard as though someone has balanced a large smartphone there. It looks like it should descend neatly out of sight when not in use but it doesn’t – it’s the same in many other modern cars, so perhaps we shouldn’t grumble.
A rotary control and shortcut buttons that dictate what’s displayed on that colour screen sit on the centre console between the front seats. Collectively, these pieces of hardware and associated software are known as iDrive, and they allow you to control the audio settings, phone connection and sat-nav. More conventional controls for some of the hi-fi’s features sit beneath the screen, and beneath those are controls for the heating and ventilation.
What’s evident from even just pulling the door shut is that the 3 Series Mk6 is very well built, and there’s a feeling of quality to the action of all its controls and to the texture of the cabin materials. After the car’s facelift in 2015 the quality of those materials, especially those of the dashboard and along the top of the doors, improved further, but if you experience an older model in isolation then you’re still likely to be impressed.
Models with optional light-coloured upholstery where this contrasting colour extends to the lower portion of the dashboard, seem a little more luxurious.
What’s on the equipment list?
All trim grades of the 3 Series Mk6, including the entry-level ES, feature climate control, DAB radio, Bluetooth connection for your smartphone, cruise control and a 6.5-inch colour screen for the infotainment system. Alloy wheels are universal, too, although their size and style differ between grades.
The climate control is upgraded to dual-zone for the SE, which also has automatic lights and wipers, as well as rear parking sensors. Gloss black exterior trim pieces, sports seats and red interior trim details identify the Sport, while the M Sport has a distinctive aerodynamic body kit, lowered and stiffened suspension, even more aggressively bolstered sports seats and leather upholstery.
In conjunction with the 320i and 320d EfficientDynamics models, which were aimed at high-mileage company car drivers, BMW offered a Business Edition trim grade. This featured sat-nav, heated front seats, Dakota leather upholstery and a BMW Business Media Package as standard.
For a short while you could also order your 3 Series Mk6 with a couple of styling packs, Modern and Luxury. Modern was based on the SE trim grade and swapped out the piano black interior trim inserts for a set made from a matt chrome material, but Luxury raised the game a little with the inclusion of plusher leather upholstery and wood veneer inserts for the dashboard and door trims.
If you see a 3 Series Mk6 badged as an xDrive, this denotes the fact that it’s four-wheel drive, an option offered for drivers who wanted optimum mobility and security through the slippery winter months. Electronically controlled dampers were another intriguing option – they automatically alter the softness or firmness of the suspension depending on what settings you put them in, and how the car is being driven. This option is a good one to hunt down if you fancy the good looks of the M Sport 3 Series Mk6 but can’t cope with the stiffness of its standard sports suspension.
From May 2014 all models fitted with sat-nav and an automatic gearbox came equipped as standard with BMW’s Proactive Driving Assistant. Even when the sat-nav is switched off, this system uses GPS data to detect when you’re approaching a bend, or roundabout, or motorway exit, and automatically instructs the gearbox to change down a gear to improve the level of engine braking.
How safe is the BMW 3 Series Mk6?
When crash-tested by the Euro NCAP safety organisation, the 3 Series Mk6 proved exceptionally safe and was awarded a full five-stars rating. Its score for adult occupant protection was a remarkable 97%, and it scored 87% in both the child and pedestrian protection categories, and 86% for the effectiveness of its safety assistance systems.
Practicality and boot space
While not huge inside, the 3 Series Mk6 seats four adults in reasonable comfort and has space for their luggage, too
As long as none of them is too tall, a driver and three passengers can travel comfortably in the 3 Series Mk6. And provided that it’s for a weekend away rather than a month-long tour of Europe, the boot will accommodate their luggage. Available as an option when the car was new was a split-folding rear seat, which enables you to carry long items such as flat-packed furniture, but a slightly tight boot aperture will dictate what size items you can transport.
How big is the BMW 3 Series Mk6?
While it’s referred to as a compact executive saloon, the 3 Series Mk6’s external dimensions may initially tax your parking skills if you previously owned a family hatchback. Its overall length is between 4,624mm and 2031mm depending on the model, and it’s 2,031mm wide and 1,429mm high.
How much space is there for passengers?
Passengers up to about six-feet tall – as long as the person they’re sitting behind in the front is no taller than they are – should find adequate space for their head, knees, shoulders and feet. A middle passenger in the back puts a big squeeze on shoulder room, which is fine for a lift back from the pub, less than satisfactory for all concerned if the trip reaches a double-digit mileage. The central part of the rear seat isn’t really shaped for long-term occupancy anyway, and the fact that whoever sits there will have to splay their legs either side of the hump in the floor (the transmission tunnel) is further discouragement.
ISOFIX child seat mounts for the two outer rear seats are standard on all 3 Series Mk6s, although the back doors don’t open especially wide, which can make manoeuvring the kids inside a bit of a pain.
Storage options include large front door bins, a sizeable glovebox, a brace of cupholders in the centre console and map pockets on the back of the front seats.
How big is the boot?
At 480 litres, the boot of the 3 Series Mk6 compares well with those of key rivals. Flat walls and floor make it easy to pack, and it will swallow a weekend’s-worth of bags for four people.
The boot aperture is tighter than it looks in some pictures, and it can limit what you can physically stuff into the boot. A 60:40 split-folding rear seat was an option when the 3 Series Mk6 was new and it allows you to haul longer items such as flat-pack furniture. The trick is, of course, finding a car that was fitted with said option.