Don't mess with a good thing. You can imagine these words hanging above the engineers and designers who created the redesigned 2012 BMW 3 Series. It wouldn't be far-fetched to call the 3 Series a legend, as it has collected countless accolades, a devoted customer base and excellent sales during its five previous generations. It has consistently been the benchmark for which all others in its price segment are judged. In other words, it's a big deal when a new 3 Series is introduced.

For this year, BMW is introducing the new sedan only. The coupe, convertible and wagon (all of which we still highly recommend) are unchanged other than gaining some extra standard equipment. As for the sedan, its evolutionary look draws liberally from the 5 Series, but the 3's new nose is a break from tradition, with headlight clusters that meet widened kidney grilles. The interior gets a far more visually interesting design than the rather plain one it replaces. The addition of three optional "equipment lines" -- Luxury, Sport and Modern -- bring with them different color schemes and trim materials that add to the 3's customization potential.

The new 3 Series sedan is larger than the outgoing car but actually weighs less, thanks, in part, to increased use of aluminum in the revised suspension. The steering is now electrically driven; this helps to increase fuel efficiency, though it's lost a bit of that trademark BMW steering feel in the process. Like all recently introduced BMW models, the 3 Series gets Driving Dynamics Control, which allows the driver to select among four modes that alter throttle response, steering effort and shift patterns of the automatic transmission.

Under the hood, the base model 328i sedan loses its naturally aspirated inline-6 in favor of a turbocharged four-cylinder that produces more power and torque and also achieves truly incredible fuel economy. BMW purists may cringe at the words "four-cylinder," but it's quicker than the old car and vastly more efficient to boot. Those purists will at least be happy to hear that the 335i's turbocharged inline-6 carries on. A new, optional eight-speed automatic transmission and a fuel-saving auto stop/start system round out the powertrain changes.

The redesigned BMW 3 Series sedan is, for the most part, improved for 2012, and yet its stronger competition makes choosing one harder than it's ever been. The Audi A4 and S4, Infiniti G and Mercedes-Benz C-Class are all excellent choices. Each of those also offers different body styles that are for the most part similarly appealing. Nevertheless, the new 3 is still a winner even if BMW decided to mess with a good thing.

The 2012 BMW 3 Series is available in sedan, coupe, hardtop convertible and wagon body styles. The coupe, convertible and wagon belong to the previous-generation body style, whereas the sedan is an all-new model.

Every body style starts off in 328i guise. The sedan comes standard with 17-inch alloy wheels, adjustable drive settings, automatic headlights, foglights, automatic wipers, cruise control, automatic dual-zone climate control, a tilt-and-telescoping steering wheel, eight-way manual front seats, leatherette premium vinyl upholstery, a leather-wrapped steering wheel, Bluetooth phone connectivity, the iDrive electronics interface and a premium sound system with a CD player, HD radio, an auxiliary audio jack and an iPod/USB audio interface.

The coupe differs with a sport-tuned suspension, while the convertible gets a fully powered retractable hardtop and 10-way power front seats with memory functions. Both two-door body styles add adaptive xenon headlights and a 60/40-split-folding rear seat. The wagon differs from the sedan's equipment with 16-inch alloy wheels and a panoramic sunroof, while not including the auxiliary audio jack and iPod/USB audio interface. None of the above include the sedan's adjustable drive settings or Bluetooth, but the latter is an option.

The 335i primarily represents a more powerful engine and is available on all but the wagon. On the sedan, it also adds 18-inch alloy wheels, adaptive xenon headlights, automatic high beams, a sunroof, eight-way power front seats (with four-way power lumbar) and an auto-dimming mirror. The coupe and convertible are similarly equipped, but lack the auto-dimming mirror and automatic high beams. The convertible adds heat-reflective leather upholstery.

The 335is coupe and convertible get an upgraded engine, sport exhaust, a sportier suspension calibration, 18-inch wheels, unique styling elements, sport seats and a sport steering wheel.

Most of the extra items on certain body styles and trims are available as options on the others. There are many other options available as well, most of which are available both within packages and as stand-alone options. These include larger wheels, an automatic parking system (sedan only), headlight washers, parking sensors, keyless ignition/entry, an active steering system, heated front seats, heated rear seats (sedan only), a heated steering wheel, a power rear sunshade (coupe only), BMW Assist emergency communications system (includes Bluetooth), a navigation system (includes BMW's iDrive electronics interface), a head-up display (sedan only), satellite radio and a Harman Kardon surround-sound audio system.

Finally, the sedan can be equipped with three optional equipment lines -- Luxury, Sport and Modern -- that include different wheel designs, color schemes, trim types, seats, steering wheels and even suspension tuning.

The 328i sedan is powered by a 2.0-liter turbocharged four-cylinder that produces 240 horsepower and 255 pound-feet of torque. Rear-wheel drive and a six-speed manual transmission are standard; an eight-speed automatic is optional. Both come with an auto start/stop function that turns off the engine when the car stops in order to save fuel. In Edmunds performance testing, a manual-equipped 328i went from zero to 60 mph in 5.9 seconds -- quicker than all its four-cylinder competitors. EPA-estimated fuel economy is 24 mpg city/36 mpg highway and 28 mpg combined with the automatic, and 23/34/27 with the manual -- these are both exceptional for the class.

The 328i coupe, convertible and wagon get a 3.0-liter inline-6 that produces 230 hp and 200 lb-ft of torque. Rear-wheel drive and a six-speed manual are standard; a six-speed automatic and all-wheel drive are optional. BMW estimates a manual-equipped coupe would go from zero to 60 mph in 6.2 seconds -- all other transmissions and body styles would be within a second slower than that. EPA-estimated fuel economy is 18/28/22 for the rear-drive coupe regardless of transmission. The other body styles and all-wheel drive achieve 1 or 2 mpg worse in each cycle.

All 335i models regardless of body style get a 3.0-liter turbocharged six-cylinder that produces 300 hp and 300 lb-ft of torque. Each body style gets the same transmission and drivetrain choices as their respective 328i versions. BMW estimates a 0-60 time of 5.4 seconds for the sedan, and in Edmunds performance testing the coupe was a little quicker than that. Fuel economy estimates for the 335i sedan are an impressive 23/33/26 with the automatic and 20/30/23 with the manual. The coupe gets a still solid 19/28/22 with rear-wheel drive and the manual. The automatic and all-wheel drive drop those estimates by 1 or 2 mpg depending on body style.

The 335is has a twin-turbocharged 3.0-liter six-cylinder good for 320 hp and 332 lb-ft of torque. There is also a temporary overboost function that bumps max torque up to 370 lb-ft. A six-speed manual is standard, and a seven-speed automated dual-clutch manual known as DCT is optional. In Edmunds performance testing, a manual-equipped 335is Coupe went from zero to 60 mph in 5 seconds. Fuel economy with the manual is 18/26/21 and 17/24/19 with DCT.

Every 2012 BMW 3 Series comes standard with antilock brakes, traction and stability control, front side airbags and side curtain airbags. The sedan gets front knee airbags. The convertible lacks the side curtains, but the regular front side airbags extend up to head level and there are also pop-up rollover hoops. The stability control system integrates several features designed to improve braking performance, such as periodically wiping the brake rotors dry when the windshield wipers are in use and automatically snugging the pads to the rotors when the driver abruptly lifts off the throttle. BMW Assist emergency communications is optional.

In Edmunds brake testing, a 328i with 18-inch summer tires came to a stop from 60 mph in 115 feet, an average distance for this type of car with summer tires.

The Insurance Institute for Highway Safety gave the 3 Series sedan the highest possible rating of "Good" in the frontal-offset, side and roof strength tests. The convertible received a "Good" in its frontal-offset crash test and the second-lowest "Marginal" score in the side-impact test.

With its new turbocharged four-cylinder base engine, electrically driven steering, multiple drive settings and all-new chassis, the 2012 BMW 3 Series sedan provides a slightly different driving experience than before. It still has sharp reflexes, but its steering doesn't offer quite as much feedback as the previous model. Driving enthusiasts will likely prefer the slightly crisper and more dynamic feel of the carry-over coupe and convertible. The new sedan does ride better and remains a wonderful long-distance cruiser, boasting both a supple ride and a hushed cabin. But in terms of being exceptionally fun to drive, the 3 Series is no longer a standout for the sport sedan class.

Still, we have no complaints about the 328i sedan's new turbocharged four-cylinder engine. It provides quick acceleration and a healthy boost to fuel economy. Most shoppers will be pretty happy with this engine. But should you want the traditional inline-6 experience, the 335i adds a huge wallop of turbo torque that's always on tap, while the 335is goes a bit further and sounds especially delectable to boot.

The redesigned 3 Series sedan cabin gets a more contemporary update compared to the other body styles, especially around the dash, doors and center console. Sharper angles and bisecting trim pieces replace the former generation's more austere lines and bulges, while trim finishes range from cool aluminum to textured faux-wood.

But BMW hallmarks remain: classic analog gauges, sensible ergonomics and a restrained overall aesthetic. The new sedan comes with three choices of equipment lines -- Luxury, Sport and Modern -- that, among other things, change the color scheme and trim type in the cabin. It's a nice touch that allows a greater amount of customization.

The base seats are comfortable and supportive, while the Sport package's purpose-built seats are even more so. Materials and build quality are exceptional; even the standard leatherette (vinyl) upholstery looks and feels better than one would expect. The convertible's available heat-reflective leather does a wonderful job of keeping occupants' posteriors cool. The intuitive iDrive electronics interface is one of the best of its kind, made better in the new sedan with a 6.5-inch widescreen display that looks like a large smartphone standing on its side. The monitor helps weave through BMW's dense menu structures, but really shines when paired with the optional navigation system.

The 3 Series' backseat is one of the more spacious in the entry-level luxury segment regardless of body style, and the new sedan's length adds a little legroom front and rear. Trunk space is average in the coupe, while the wagon offers a maximum cargo capacity of 61 cubic feet. The convertible offers a reasonable cargo hold when the hardtop is up, but predictably shrinks considerably when the top is lowered. Still, it's possible to store a standard roller suitcase back there or two smaller bags.