BMW M135i / M140i & M235i / M240i Dynamics Package Upgrades

Birds B1 and B2 Dynamics Packages for the BMW M135i / M140i and M235i / M240i are combinations of exclusive suspension and differential performance upgrades, developed in-house on our own development cars, designed to transform the ride, handling and traction of the standard car on UK roads.

Prices and Applications

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Package breakdown

Quaife ATB limited-slip differentials increase the torque presented at the tyre contact patch with the road, which increases the force exerted on the road, which, in turn, increases the rate of acceleration. In low grip situations, the standard "open" diff. allows one wheel to spin, triggering the traction control and limiting the engine power. The Quaife ATB Differential prevents the wheel with the least grip from spinning, traction control is therefore not triggered, and the car accelerates to it's true potential. Check out Autocar and EVO Magazine's Quaife review on the M135i.


B-Series Sport Suspensions – Birds' B1 (M135i/M140i) and B2 (M235i/M240i) Sport Suspension. Standard suspension systems are a compromise between comfort and safety components whereas the sporting expectations play a minor roll. After all, the high costs involved in the long suspension development process must also be taken into account. Birds' finely tuned B1/B2 sports suspension offers a more sporty drive and maximum safety without loss of comfort – an uncompromising alternative perfectly designed for our bumpy U.K roads. Now available in "OE Black".


A note about tyres...

If your M135i / M235i is equipped with Run-flat tyres, we cannot stress enough how important it is to rid yourself of these performance sapping devices! In our opinion, the arguments proposed by BMW for these tyres is totally misjudged, and we know of no customer who regrets installing conventional tyres.

A second note. All tyre brands do not perform similarly. Our recommendations are based on UK road conditions, and provide the best in wet weather grip and handling. If you want race style tyres, we can provide them.

Additional options

Anti-Roll Bars – B1/B2 anti-roll bars complement the chassis balance and trim. Fast drivers will immediately note the prevalent under-steer inherent in the standard BMW chassis. As a consequence we provide significantly more rear stiffness than the front, biasing away from under-steer. Again, these stabilisers have been manufactured to our own specifications. These are not off-the-shelf, close-enough items.



Brakes – Alcon Ø365x32mm curved vane ventilated and grooved discs for the front axle, featuring low weight alloy hubs, with a unique floating rotor system to prevent vibration and fade. Six piston alloy callipers for reduced weight and mighty stopping power. The feel and progression of these brakes allow fierce braking right up to the point of ABS actuation, both in the wet and dry. Fully protected against corrosion, and they work from cold right up to racing temperatures. The M135i requires  a minimum of 19” wheels.








Why we did it

Our mission at Birds? To create a high-performance, real-world alternative to BMW’s M-Power creation, uniquely designed for British roads.

Every year we purchase the latest non M-Power BMW, analyse the car for its strengths and weaknesses, and develop upgrade packages with a hollistic approach in an attempt to deliver a truly gratifying "ultimate driving machine" without sacrificing the practicality and elegance of the standard car.

For many of us, BMW’s M-Power models aren’t the right choice for an all-round car. They’re expensive (to buy and to run), uneconomical, and too aggressive.

But while BMW’s 'm-performance' models such as the M135i, M140i, M235i, M240i, etc. are fantastic all-round packages, and tick all of the boxes for many, they fall slightly short of delivering pure driver enjoyment.


The BMW M135i and M235i were used as base cars for development of our upgrades


The ride and handling is one of those shortfalls. Given that the suspensions on these cars were developed on German roads, it didn’t surprise us to find that the ride quality is quite poor on our bumpy British B roads (as was the case with the previous E82/E87 1 series).

Although slightly improved compared to the last 1 series, a 'fidgety' rear end and lack of composure when pushing on over these road surfaces was clearly evident.

The lack of traction is another. Equipped with stiff suspensions, engines producing large torque figures, and sometimes run-flat tyres, the absence of a mechanical limited-slip differential is very noticeable for anyone during quick driving, especially in less than perfect conditions. RWD performance cars need power to both wheels (the M-Powers always come equipped with an LSD, of course).

The Birds Dynamics Package is designed to transform the standard car’s ride, handling and traction on British roads. No more crashing into pot holes, no more sudden changes of direction or lack of composure on bumpy roads, and no more power-sapping traction control intervention. 



Below are some of the reviews of our Birds B1 M135i and B2 M235i models. To see all reviews, please click here.

"Our M135i out-punches the M2 by 25bhp and 51lb ft of torque, so it feels stronger through the mid-range and more urgent near the redline. But with less power to deploy to the road, and wider tyres with which to do it, the M2 does have better traction..."


"Not only was the ride quality better than before, ultimate body control improved on our bumpy B-roads and the steering feel improvements were in a different league."


Editorial - F20 M135i - Long term review before and after B1 upgrades - Autocar Online - January 2018

Follow Autocar's long-term M135i review online here, including details on our B1 upgrade development project and their thoughts on the results. 


Editorial - F22 M235i - Autocar Magazine - July 2017

"Without exaggeration, the B2 conversion is transformative. There’s more composure in the ride quality and the uprated suspension is much better equipped to deal with uneven roads."


Editorial - F22 M235i - EVO Magazine - June 2017

"The meaty engine responses are sharp without being edgy and delivered without the faintest hint of reactive nerves from the chassis. Although the helm answers inputs alertly and accurately, it filters out the rigours of bumpy roads with poise..."



Kevin Bird on the Dynamics Package development

"The primary aim? To provide the driver with the best possible combination of ride, handling and traction attributes for fast and safe road driving.

Secondly, and perhaps more importantly, to give the driver feedback. How to describe this... The thrill of driving? The joy of driving? We don't think anyone has yet put the meaning of this into words. Happily, though, we are confident that the products of our work adequately translate into the correct experience. Maybe it's easier to feel it rather than express it.

Finding the problems in the standard car isn't too hard. With more than 300hp at the driver's command, yet without a limited-slip differential to distribute that power and torque to both rear wheels, there is no possibility of gaining 100% traction in the first, second, or even third gear without some artificial regulation of the engine performance. There is hard evidence gained via data logging that the engine performance is limited in the engine management in the first few gears, and that's before the irritating traction control chimes in!

Interestingly, the traction control warning lamp has also been suppressed, and we can only imagine that BMW don't want the driver to "see" the results of pedalling the car too hard.

Then we have the ride quality and body control issues. Apart from the suspension tune, which BMW invariably get wrong for UK roads, the quality of the dampers seems to be the achilles heel of all the F-Series chassis. If you have run to the additional expense of Electronic Damper Control (EDC), you might be particularly disappointed to find that Comfort is too soft for meduim speed driving, Sport is too hard and crashy for slow speeds, and is definitely not at all pleasant on bumpy roads at high speeds. Those settings also interfere with throttle and gear change attributes, when they are not wanted. Even if you like the attributes, why do you have to press a button to get the car to handle properly?

Irritatingly, it's clear that BMW do know how to tune a chassis properly. Think of the 1986 E30 M3, with it's truly wonderful chassis, body control, ride and handling, superb steering feel, an altogether wonderful driving experience.

We believe our B-Series Dynamics Packages get very close indeed, and certainly match the M3 for body control and traction, even with more power than the M3. Maybe we could improve the steering more than we already have, but that would be beyond the realms of reasonable affordability.

Speaking of which, significant efforts were made to contain body roll without resorting to the useful method of adding anti-roll bars to the package. Yes, they control the body roll, and can be tuned to bias the chassis away from under-steer. However, there are unwanted characteristics such as "head-rock" where they react to changes in camber when running in a straight line. Yes, it feels sporty, and reduces body roll, but if that can be achieved through tuning of the dampers, then it's an expense that can be avoided.

So we have packaged the Quaife, together with our own springs, Bilstein dampers specially valved to our own specifications, alongside increased track width for the front axle, and front and rear geometry changes to improve stability. We are totally sure there is no more competent package out there.

Just going back to the E30 M3 for a moment. The original version on 15" wheels was pretty much perfect, but the design was "evolved" into something different. BMW M were tasked to make the car sportier because some customers demanded it. They installed 16" wheels, different dampers and springs along with some stiffer bushings, along with some engine tweaks. Some would say that the car handled worse, but many believed it was better, and certainly felt "sportier".

We can't speak for every customer, but there will definitely be some out there who want an additive sportive flavour. For that reason, we also offer anti-roll bars biased to remove under-steer, and will also cater for those who express a desire for 19" wheels. The Joy Of Driving has no measurable units. It's entirely dependant on what satisfies each individual."


Our promise

As with all Birds Conversions, expert advice comes as standard. We treat all customers as individuals, and recognise that every individual has their own set of desires and criteria. We have more than 30 years experience in the BMW tuning arena, more than any other organisation in the UK, and know how to get the best performance from BMW cars. We are enthusiasts and are happy to discuss in detail every aspect of the performance of your car. Options are many, but please let us guide you toward 'Ultimate BMW Performance'. We will deliver pure driver appeal and superior performance from your BMW.