BMW M135i long-term review

Why we travel: To find out how you can improve this used BMW M135i with a little help from our friends the Birds

Month 1 Month 2 Month 3 – Specific

Life with a used BMW M135i: 3 Month

To change the M135i tyre pressures – 18 October 2017

Having replaced the suspension with springs and shock absorbers, I have played with tyre pressures.

I wanted to find the perfect compromise between ride quality, tire grip and stability. I found the 29psi was great for the ride and grip, but the tires squidged around too hard in a curve.

But 37psi distorted the race and did nothing for the taking, so I have settled on 32psi. Perfect.

Mileage: 32,150

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Life with a used BMW M135i: Month 2

To deal with the M135i suspension – September 13, 2017

Perhaps the single biggest upgrade that will do to our used M135i is also the first – the suspension.

Outside of BMW’s Electronic Damper Control equipment in favour of a set of Eibach springs with passive Bilstein shock absorbers, both optimized specifically for the M135i.

The birds, the specialist we’re working on this project, recruited the former pilot James Weaver and experienced race engineer Peter Weston to optimize the new suspension.

Between them, Weaver and Weston has selected appropriate off-the-shelf springs for the car, while also specifying the right shock curve of Bilstein, who built the damper kit accordingly.

The result is that the Birds suspension upgrade for the M135i is the owner. You can’t get anywhere else. The new suspension took half a day to measure, at a cost of £1554.23 with the installation, but not VAT (which brings the total to £1865.08).

“I drove the car standard and it was a little bit the eyes to say the least,” says Weaver. “The ride quality was pretty poor. The problem is that in Germany, the new cars have to be able to do 124mph, five-up and a full load boot, normally on smooth roads.”

Accordingly, as Weston explains, modern cars are desperately over-damped most of the time, when they have only one or two occupants. They are, moreover, often is not optimized for the UNITED kingdom is broken, bumpy road network.

This means that most of the cars, the M135i is included, they offer a lot of room to improve, which certainly tallies with my experience of the car.

Weaver and Weston conducted a standard test M135i, using a loop of about four miles – in a large part of the narrow and bumpy lane – near the Birds’ Buckinghamshire home.

They found that the ride quality was poor, mainly because there was too much rebound in the standard set-up, and the car also lacked grip, traction and steering precision.

“The damping I have incorporated in the shock is what we have learned over the years with James in a racing environment, with a high-performance car on a bumpy circuit of Sebring,” says Weston. “That experience taught us a lot about how to support a car on the springs and the safety of damping that allows you to go over bumps. Blows the theory that for a car good on bumps you need soft springs – which is not always the case.”


The Birds M135i project really gets going today. To get the springs and shock absorbers mounted. Will make a huge difference.

— Dan Prosser (@TheDanProsser) August 11, 2017

The set-up, the pair eventually arrived at includes springs that are 15% stiffer at the rear, and about 10 percent stiffer at the front, with a 10mm drop in ride height over the front axle.

The returns of damping is much less bounce, allowing a certain wheel to quickly remove out of his wheel rather than hang in there.

If the exceedance of a bump in the road, a pothole or sunken drain cover, less rebound damping will massively improve the ride quality.

I’ve covered a couple of hundred miles on the new set-up and is definitely a great step forward. What surely is not very stiff, track-focused set-up.

Instead, the car now feels much more stable on bumpy roads at speed. No longer jumps on with the tires losing contact with the ground.

Is more comfortable even now, the new suspension rounding-hole and choke on the broken, rough patches of asphalt.

The body control is also much better and the car no longer feels as if it is going to bounce off the road, over the ridges and the undulations of the ground.

The steering update, in the meantime, is simply a pair of spacers 10mm on the front axle that subtly adjust the geometry. The steering now feels sharper and more direct, even if it is not a night-and-day improvement.

The next update will be a Quaife limited-slip differential to further improve traction and make the car easier to control on the throttle right at the limit of grip. Only then will we be able to go anywhere near the engine.

Mileage: 31,706

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Life with a used BMW M135i: 1 Month

Welcoming the BMW M135i to our fleet – 16 August 2017

My new long-term test car is not new. In fact, it is coming up to five years.

By today’s standards, the throwaway society, that probably means that it is halfway to the scrapheap already, but we have big plans for it anyway.

The BMW M135i was launched in 2012, making this 62-plate example, one of the first cars. The M135i has been so well received by the press and car-buying public that couldn’t read more than 15 internet forum post without someone telling you to get one.

Five years on, the cheapest, leggiest M135is have lost more than half of their value. You can take a 70,000-mile car today for about € 14,000, which looks like a very good value, in fact, for a modern rear-wheel drive hatch with the 316bhp.

This particular car is covered of 30,000 km and a cost of £17,500. The spec is only on spot: the three-door, manual transmission, black leather.

The M135i cost a fiver under £ 30,000 when it was new, which meant that there was not much more expensive than high-performance Volkswagen Golf, Renault Sport Méganes, and the like. But it was more powerful, had more prestigious badge, and, of course, much more rear-wheel drive. Little wonder that it has proved so popular.

Years later, it’s still an interesting package. The turbo six-cylinder engine gives strong performance in the straight line, the rear-driven chassis is well balanced, and much less interesting side, it is practical and quite stylish.

However, it is actually a bit flawed. I can’t say too much on this style, except that I never much liked the large, triangular headlights, but I like that you can tell just from looking at it, in which the energy is sent: the cabin is pulled back over the car and the distance between the base of the windshield and the front axle line to give it away.

The biggest problem, however, is to do with the dynamics. Now, the M135i is a very good car up to about seven tenths, but when you really start to peddle, or when the road is particularly difficult, everything starts to unravel.

There is no steering precision, or the tight-fisted body control that you need to really fling it around with confidence.

And when you start to lay the ridges and small jumps and compressions in the mix, the damping feels all at sea. No matter which of the two shock absorber mode of choice, the frame is never able to smooth out lumps and bumps in the road, but also to maintain the body locked under tight control.


New long-termer the day today! Even if the car is not really new at all…

— Dan Prosser (@TheDanProsser) July 7, 2017


To be honest, only the best cars do those two divergent things at a time, with any degree of flair.

The M135i, you soon find yourself give up, because the body is to pull up and down like a boat in a storm, or because the rear is tracking some strange circular pattern behind you as you bob up and down while flopping and out of the curve.

And then there is the lack of a limited slip differential. For the most part, that is not really a problem at all, but this does not mean that the car leans on its traction control, all too often, even in the wet. And when you are really getting after the thing in the wash and you have all those systems off, it is frustrating to feel downloaded to the inside rear wheel spin up, unnecessarily, as you try to neatly slide out of a corner.

There is, therefore, a great amount of space for the improvement. Then, this M135i is our new design of the car and in the coming months, we intend to update all of the most important bits and pieces to turn it into a vehicle we believe it should always have been.

Work with BMW tuners Birds, we’re going to replace standard, under the specified suspension with much higher quality Bilstein components developed specifically for the M135i, we’re going to fit a Quaife limited-slip differential, and we’re going to lift power from somewhere, approaching 400bhp. You can still do a couple of other changes, too.

When it is up-to-date Birds B1 specification, it should be quite a car. We tested the company M235i demonstrator – updates are interchangeable between the sedan and coupe and found it to be a great improvement over the standard machine.

What makes us so sure that we, automobile magazine, and an independent garage, can build a car better than BMW?

Each component in a mass-produced car is built to a strict price units. The cars are designed for a wide cross-section of drivers and countries on opposite sides of the world. We, however, are able to spend a lot more on the suspension parts, BMW could justify and we also have a precise idea of how you want the car to feel once it is finished.

The M135i will be updated in the course of time, you can follow our progress in these pages.

Please do get in touch via the usual channels and let us know what you think of our new project car.

Second opinion

The M135i promised a better car and it delivered.

The standard machine vertical control of the body is the thing most in need of improvement.

A slippy diff has the same odds of damaging the handling balance, as it has done to improve, so hopefully it will be well-set. I look forward to finding out.

Matt Saunders

BMW M135i specific

Specifications: Used Price £17,500; The New Price Of£29,995

Test data: Engine 6 cyls, 2979cc, turbo, petrol; Power to 316bhp at 5800 rpm; Torque 332lb ft at 1250-5000rpm; maximum speed 155mph; 0-62mph 5.1 sec; Sustained fuel economy 35.3 mpg; Test of fuel economy 30.0 mpg; CO2 188g/km; Flaws None; the Costs of Suspension upgrade (£1865)

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