The AC Schnitzer ACS1 Improves The M135i Massively, But Doesn't Fully 'Fix' It

When we drove the inline-four BMW M135i for the first time a few years ago, we didn’t much care for it. In some ways, it improved upon its six-pot predecessor, namely with a more sorted-feeling chassis. But sweet lord, was it dull for a 302bhp car.

The engine lacked sparkle, the all-wheel drive system had no interest in making things excited at the rear axle, and the gearbox wasn’t brilliant either. And despite having ditched the old car’s longitudinal, rear-drive layout for a less interesting but easier to package transverse one, it didn’t seem any roomier inside.

BMW, for its part, recently treated the M135i to a whole host of dynamic tweaks despite the car being relatively young. We’re yet to try one of these fettled cars, but what we have driven is an aftermarket take on the car from AC Schnitzer. Enter stage left, the ACS1.

What it doesn’t have is more power. Not because the engine can’t take it - the Aisin-supplied eight-speed automatic gearbox is the limiting factor. The highest output the German tuner could safely extract would be around an extra 20bhp, a modest increase deemed not worth it. Instead, the focus here is on the chassis and the looks.

On the latter front, we’ve lots of good news. No, we’re still not quite used to the ‘F40’ 1er’s front end, but it doesn’t seem so bad in light of even more controversially-styled modern BMWs to emerge since. This one also looks a lot snazzier at the front end thanks to some subtle bronze trim pieces, notably for the kidney grilles and the air curtains. Just below is a sizeable front splitter, but nothing low enough to make you sweat about speed bumps.

Filling the wheel arches without looking excessively large is a set of 20-inch ‘AC4’ wheels, while at the back, there’s a neat little ‘bridge’ that clips onto the middle of the factory-fitted boot spoiler. The interior has been largely left alone, save for the addition of some lovely CNC-machined aluminium shift paddles.

In terms of the chassis, the brakes have been left alone, but that’s just fine. The standard stoppers are more than up to the task of hauling the M135i to a standstill, and with no more power extracted from the ‘B48’ inline-four, extra braking clout simply isn’t needed. The chassis has undergone a pretty sizeable change, though, with the ACS1 swapped onto bespoke ‘RS’ adjustable dampers that can drop the ride height by 30 - 40mm.

With the aesthetic tweaks, more low and the very sage choice of San Remo Green paintwork (referencing the Nurburgring‘s ‘Green Hell’ nickname, along with the ‘HEII ACS’ number plate), this is easily the best-looking current 1-series we’ve yet seen. And yes, it is far more interesting to drive.

There’s a new carbon-tipped exhaust adding a touch more bass to the inline-four’s soundtrack, which remains uninspiring on the whole. What makes a far greater difference is those dampers, here set to a 30mm drop. A lower centre of gravity makes for a car that’s keener to change direction, and the extra stiffness means body roll - hardly an issue in the stock car anyway - is non-existent.

Plus, the previously numb steering now has a whole lot more life in it, giving noticeable kickback through the feel. This is not a car you’re going to drive and forget about immediately, as was the case before. It’s exciting and feisty, and yet still endlessly surefooted thanks to the M135i’s all-wheel drive system. On a cold, damp day like today, there’s not much that’d get away from this thing.

As soon as I heard the words “lowered by 30mm” before driving this car, alarm bells started ringing. That’s a sizeable drop for a road car, but the decrease in ride height and suspension travel hasn’t resulted in an unacceptably firm ride. Around town, the damping can be a little abrupt, and on rougher roads, you are in for a choppy time, but it settles at higher speeds.

It’s still a very committed option, though. If it was me, I’d want to be taking my M135i to the track fairly often before considering the suspension stuff. What all owners should be eyeing up, however, are the paddle shifters. For a relatively low cost (£309.51 on their own), they make manual control of the car’s auto ‘box so much more interesting than when operating the miserable little pieces of plastic BMW fits on the wheel.

Other elements aren’t quite so cheap. The splitter for example is £872.14, while the wheels are £3151.32 before tyres are taken into account. The RS dampers are £2577.17 (£104 more if you’re swapping from adaptive dampers), or if you’d prefer there’s a lowering spring kit that’s £387.27. The rear spoiler is fairly affordable at £328.04, and finally, the exhaust is £1820.78.

Together, this stuff makes for a massive improvement. But enough of a leg-up to worry some of the hot hatch greats around right now? Not quite, and that’s all down to the car AC Schnitzer has to use as a starting point. This is a clear step in the right direction, though, and the upgrade programme is well worth a look if you are set on an M135i despite our best efforts to put you off.

The good news is all of this stuff fits on the more engaging front-wheel drive 128ti. The dampers, the paddles, some of the aesthetic bits would go nicely with a power upgrade that lifts the 128ti into line with the M135i’s output, although the latter is something AC Schnitzer doesn’t offer just yet.