BMW M135i F21
Specifications
Overview
| Country of origin | DE |
|---|---|
| Fuel type | Petrol |
| Drivetrain | RWD |
| Chassis code | F21 |
| Gearbox | 8-speed ZF automatic |
Performance
| Power | 324 PS |
|---|---|
| Torque | 450 Nm |
| Kerb weight | 1515 kg |
| Power-to-weight | 211.2 bhp/tonne |
| 0-62 mph | 5.1 sec |
| Top speed | 155 mph |
Powertrain
| Engine | 3.0-litre straight six |
|---|---|
| Cylinders | 6 |
| Induction type | Turbocharged |
Running Costs
| Combined MPG | 37 mpg |
|---|---|
| CO2 | 175 g/km |
The BMW M135i F21 arrived in 2012 as the three-door version of the second-generation 1 Series, and it was a very BMW-flavoured answer to the rising premium hot-hatch market. Where many rivals were moving toward transverse four-cylinder engines and all-wheel drive, the M135i kept a longitudinal engine layout, rear-wheel drive, and a turbocharged straight-six. BMW’s own launch material called rear-wheel drive “unique for a vehicle in this class” and described the M135i as the first BMW M Performance model for the compact segment, using a 3.0-litre straight-six with 235 kW / 320 hp.
On paper, it was extremely serious for a 2012 hatchback: 320 hp, 450 Nm, a choice of six-speed manual or eight-speed automatic, and rear-drive as standard, with xDrive versions appearing later in some markets. BMW’s later retrospective lists the rear-drive manual at 0–100 km/h in 5.1 seconds, the rear-drive automatic at 4.9 seconds, and the xDrive automatic at 4.7 seconds, with top speed electronically limited to 250 km/h. It was not a full M car like the 1M Coupé, but that was part of its appeal: Top Gear framed it as a fast, entertaining, “not-quite replacement” for the 1M that was also much cheaper.
Its impact came from being different rather than simply being the fastest. The Mercedes-Benz A45 AMG, Audi S3, Audi RS3, Volkswagen Golf R, and Golf GTI were all part of the same broad hot-hatch conversation, but the M135i offered a small-hatch version of the classic BMW formula: big engine, rear-drive balance, and understated styling. Autocar praised its value, noting that even with the optional eight-speed auto it was around £5,000 less than the Mercedes-Benz A45 AMG when new, while also describing it as outstanding value for money. Evo later grouped the Golf R and Audi S3 as direct rivals and highlighted that the M135i’s engine felt more responsive and characterful than the S3’s, even though the BMW was not the final word in body control or steering feel.
As a driver’s car, the M135i was quick, compact, and a bit unruly in a way that made it memorable. It had huge mid-range shove, a smooth six-cylinder soundtrack, and enough rear-drive adjustability to feel more like a small sports saloon than a typical hot hatch. The downsides were also part of the character: it could feel firm, the steering was accurate but not especially rich in feel, and the standard open differential meant it was not as sharp or traction-rich as it might have been with a factory limited-slip diff. Evo noted that a limited-slip differential was available as a dealer-fit option, but that most cars would not have it.
Reliability reports are generally more positive than frightening, but the M135i is still a high-performance turbo BMW, so condition matters. What Car? says the engine and gearbox “tend to be bulletproof” and that owners report few problems, while also advising buyers to check bodywork, wheels, alignment, brakes, tyres, exhaust smoke, and full service history because many cars will have been used hard. Autocar’s used buying guide is more specific: it flags water pump and thermostat issues, occasional coil-pack problems, possible carbon build-up from too many short journeys, wheel bearing failures, worn front ball joints, bent wheels, and rear brake wear caused by hard driving and stability-control intervention.
The engine itself, the N55, is usually regarded as one of BMW’s better modern turbo straight-sixes, but it has known weak points. Commonly reported areas include valve-cover leaks, oil-filter-housing gasket leaks, oil-pan gasket leaks, electric water pump failure, charge-pipe cracking, ignition wear, and cooling-system plastic fatigue. FCP Euro’s N55 guide describes the engine as generally reliable but still prone to classic BMW straight-six oil leaks and electric water-pump/cooling issues, and it notes that the factory charge pipe can crack as the plastic ages. In short, a standard, well-serviced F21 M135i can be a brilliant used hot hatch; a badly modified, overheated, oil-leaking, or maintenance-starved one can quickly become expensive.