AC Schnitzer’s recipe is usually this: extract more power from a BMW engine, trim some fat from the chassis, and then add some glitz inside. The transformation from 1 Series M135i into ACS135i is a bit timid.

Problem is the hot hatch’s 8-speed automatic gearbox. The turbo four 2.0-litre engine’s 302bhp output is more than it can handle, so AC Schnitzer didn’t add any power.

It has instead fitted its own carbon-tipped exhaust system (PS1736), which is just like the factory system. Also, it has its own flow-formed 20in wheels (20ins) and coilovers (PS2457). AC Schnitzer also makes the suspension. Although its height, bump, rebound, and rebound can be adjusted, they come with the preferred settings of this German company.

You can also purchase a front splitter (PS831) and spoiler add-ons (PS313) as well as metal pedals (PS188), black anodized-aluminium gearshift paddles (PS295). The full conversion cost is PS11,584, including painting and fitting.

The ACS1 immediately feels more serious than the M135i thanks to the new suspension and wheels. The road can be felt through the seat and steering wheels. Even with only a thin layer of rubber on the big tires, suspension still isolates most of the real nastyness below.

The turbocharged engine is still very characterful, even with the new exhaust system. It is purposeful, practical, but not memorable.

This is also true for the gearbox. It’s too stubborn to be ignored. The shifts are blurred and slow. It lacks the snappiness of modern cars, nor the whip-crack efficiency that dual-clutch units.

The ACS1 is a stunning vehicle. The new suspension gives you more control and a better sense of the car’s grip. This makes BMW’s hot hatch a true driver’s vehicle.

Although AC Schnitzer’s modifications may seem small and expensive, the impact they make is far greater than you might initially think. They make the M135i more lively and intense and the M135i behaves with the same credibility.