Alongside the initial three-door model revealed here, BMW is also readying a five-door version that is tentatively planned to go on sale in the UK in November.
The M135i is powered by the latest take on BMW’s widely used N55 engine. Recently launched in the 640i coupé and convertible, the 3.0-litre straight six uses a twin-scroll turbocharger along with BMW’s patented Valvetronic variable valve control and double Vanos variable camshaft control systems, along with the latest in piezo valve-guided direct injection to deliver 316bhp at 5000rpm and 332lb ft of torque at just 1350rpm.
Channelling drive to the rear wheels is a standard six-speed Getrag manual gearbox, or an optional eight-speed automatic from ZF — both featuring stop-start and brake energy recuperation functions.
The M135i’s outputs aren’t quite a match for the 335bhp and 369lb ft of the older N54 twin-turbo 3.0-litre unit used in the discontinued 1-series M Coupé. It also fails to match the 335bhp of its main rival, the all-wheel-drive Audi RS3 Sportback, although the M135i matches the 332lb ft of the RS3’s turbocharged 2.5-litre, five-cylinder petrol unit.
BMW claims, officially, that in manual form the M135i is capable of cracking 0-62mph in 5.1sec. The eight-speed automatic version cuts this figure to 4.9sec. The fastest rival, the RS3 Sportback, hits the same mark in 4.5sec.
The new go-fast 1-series also delivers a 50-75mph fourth gear split of just 4.3sec, a standing kilometre time of 23.9sec and a top speed governed to 155mph.
Combined economy is put at 35.3mpg for the manual and 37.7mpg for the automatic. The respective CO2 figures are 188g/km and 175g/km.
A claimed kerb weight of 1425kg gives the most powerful 1-series hatchback yet a power-to-weight ratio of 222bhp per tonne. In comparison, the 1575kg RS3 packs 203bhp per tonne.
The M135i is distinguished from its standard three-door 1-series siblings by an aggressively styled body kit developed in-house at BMW’s M division.
The sculpting includes a deep front bumper with larger air ducts for increased engine cooling, chunkier side sills under the long frameless doors, shapely mirror housings, a prominent spoiler atop the tailgate and a heavily reworked rear bumper with a blackened lower section housing two chromed tailpipes.
The exterior styling changes ensure the M135i retains the same frontal area as other new three-door 1-series models, but the drag coefficient rises from 0.31 to 0.33, due mainly to the larger wheels and tyres.
BMW M division insiders have already begun talking up the M135i’s on-road talents, suggesting its standard rear-wheel drive layout will ensure that it offers inherent dynamic benefits to lift it above the front-drive and four-wheel-drive competition.
As with every model developed by BMW’s M division, it has undergone extensive chassis testing, including a 6000-mile programme at the Nürburgring Nordschleife circuit in Germany.
The new car rides on a reworked version of the standard 1-series’ rear-wheel drive chassis, with MacPherson struts up front and a five-link arrangement at the rear. Stiffer springs, dampers and bushes give the car a lower ride height than other new three-door 1-series models.
Included as standard are uniquely styled double five-spoke 18-inch wheels — 7.5 inches wide up front and 8.0 inches at the rear — shod with 225/40 and 245/35 tyres respectively.
Further changes have been directed at the steering; the electro-mechanical system has been tuned for added directness and more urgent response.
The brakes, too, have been upgraded and feature 340mm ventilated discs up front and 345mm ventilated discs at the rear.
They are grabbed by newly developed four-piston calipers up front and two-piston calipers at the rear — all bearing a blue colour scheme and sporting the stylised M logo of BMW’s M division, which has been responsible for the development of all the company’s new M Performance models.
From November onwards, BMW will offer a four-wheel drive option with a similarly powered M135i xDrive, although this won’t be sold in the UK. British buyers will, however, be able to choose a five-door M135i from this November.