If your BMW F20/F21 M135i or M140i feels fast in a straight line but nervous in corners, you’re not alone. Factory suspension geometry and soft bushings limit front-end grip and rear stability – especially during fast road or track driving. The following BMW M135i/M140i suspension upgrades fix these issues and more…
From our experience setting up the M135i and M140i for fast road and track use, the same themes appear repeatedly: limited front-end grip, vague steering under load, and rear axle movement when accelerating hard.
The good news is that the core platform is excellent – it simply needs proper geometry and solid mountings to come alive. Below are key upgrades manufactured by Suspension Secrets in the UK that transform the F20 and F21 M135i/M140i chassis.
F2x Suspension & Handling Overview
The M135i was manufactured from 2012 to 2016 with an ‘N55’ straight-six turbo engine producing 320hp. The replacement M140i arrived in the summer of 2016 with a 340hp ‘B58’ motor, and continued in production until mid 2019. Six-speed manual and eight-speed automatic transmissions were available.
The F2x M135i and M140i use MacPherson strut front suspension and five-link independent rear suspension. Staggered 18- or 19-inch wheel and tyre setups could be teamed with Adaptive M dampers.
The layout itself is fundamentally strong, however BMW made compromises in the bushings, alignment settings and geometry control. BMW engineered these cars for daily comfort first, fast road driving second.
When driven enthusiastically, that compromise becomes obvious.
M135i & M140i Suspension Limitations
From our testing – both on road and track – the same traits repeatedly appear:
- Noticeable front-end understeer
- Limited factory camber adjustment
- Soft front control arm bushes affecting braking stability
- Rear axle movement under hard acceleration
- Inconsistent rear toe control
- Body roll during quick direction changes
- A slightly vague steering feel
None of these problems are dramatic in isolation. But when combined, they limit confidence when pushing on. The M135i and M140i feel quick in a straight line yet unsettled when really leaned on through corners.
The good news is that these issues can be resolved with bolt-on suspension upgrades.
Common Handling Problems (And How To Fix Them)
The BMW F2x M135i and M140i suspension upgrades detailed in this guide allow you to achieve the following…
F2x M135i / M140i Suspension Fixes:
1. Increase front camber and significantly reduce understeer
2. Improve the clarity and weight of steering communication
3. Reduce unwanted geometry change caused by soft factory bushes
4. Stabilise rear toe under load and increase traction on corner exit
5. Enhance overall handling precision and consistency
With these changes implemented, the F2x chassis responds to steering, braking and throttle inputs far more enthusiastically. Turn-in becomes sharper, the front axle generates more grip mid-corner, and the rear feels much more planted.
BMW F2x M135i & M140i Suspension Geometry & Alignment Setup (Top Tip)
A proper geometry setup ensures all suspension upgrades perform at their absolute best.
BMW’s factory alignment settings are conservative. They’re designed for tyre longevity, ride comfort and broad market appeal rather than enthusiastic driving.
Benefits of a professional fast-road or track alignment:
- Increased front negative camber
- Optimised rear toe settings
- Correctly balanced chassis side-to-side
- Maximised caster angle (where possible)
Corrected geometry improves turn-in response, reduces understeer and enhances steering feel. It also increases traction on corner exit and improves tyre wear consistency.
Even on a completely standard M135i or M140i, corrected alignment alone makes a noticeable difference. However, you need more adjustment range than the factory provides to fully unlock grip.
That’s where Suspension Secrets upgrades come in…
Essential BMW M135i & M140i Suspension Upgrades
This section covers essential BMW F20/F21 M135i and M140i suspension upgrades that serve as a great first step in your pursuit of handling improvements. These upgrades form the basis of Suspension Secrets handling packages and are the ideal starting point for both road and track-focused builds.
Adjustable Camber & Caster Plates
The standard F20/21 does not run enough front camber for hard driving. As you load the outside front tyre in a corner, the tyre rolls onto its outer shoulder. That’s where much of the factory understeer comes from.
Adjustable camber plates allow significantly more negative camber to be applied to the front axle.
Benefits of M135i & M140i Camber Plates:
- Sharper turn-in
- More front end grip mid-corner
- Reduced outer tyre shoulder wear
- Increased steering feedback
When combined with the increased caster manufactured into our camber plates, you also gain dynamic camber as steering lock is applied. The steering becomes more communicative and weighted – something these cars benefit from greatly.
For fast road use, moderate camber works beautifully. For track use, higher camber settings transform consistency and front-end bite.
Solid Front Control Arm Bushes
One of the biggest hidden weaknesses in the F20 (five-door) and F21 (three-door) chassis is the front bushes.
BMW fitted soft rubber, oil-filled bushes in the front lower control arms. Under braking and cornering loads, these bushes flex. That deflection changes suspension geometry dynamically, which is why the car can feel slightly vague under heavy braking or initial turn-in.
Replacing them with Suspension Secrets Solid Front Control Arm Bushes eliminates that unwanted movement.
Solid Bushes Improve
- Braking stability
- Steering precision
- Consistency under load
- Front end confidence
The steering feels more direct. The car holds its geometry instead of moving around on soft rubber. For fast road cars, this is one of the most worthwhile upgrades you can make.
Adjustable Rear Toe Arms
If there’s one area that causes rear-end nervousness in the M135i and M140i, it’s rear toe compliance.
The factory rear toe arms use soft bushes that allow the rear wheels to steer slightly under load. When accelerating out of a corner, that movement can make the rear feel unsettled.
Solid-mounted adjustable rear toe arms from Suspension Secrets solve this issue completely.
What Rear Toe Arms Fix
- Maintain consistent alignment under load
- Improve traction on corner exit
- Reduce rear steer effect
- Increase confidence on throttle
Once fitted and correctly aligned, the F2x rear axle feels far more planted and predictable – particularly on the more powerful M140i models.
M135i & M140i Suspension Packages Explained
For owners wanting to overhaul the chassis, Suspension Secrets offers three staged handling packages, plus a full kinematics solution for serious builds.
Handling Pack 1 (Fast Road)
Designed for fast road use, this package focuses on eliminating the most significant compliance issues while retaining daily usability.
This package includes:
- Suspension Secrets Adjustable camber plates
- Suspension Secrets Solid front control arm bushes
- Suspension Secrets Adjustable rear toe arms
- Supporting components to optimise geometry
- Lowering springs or coilovers (if required)
Best For: Enhancing handling performance on the road
Handling Pack 2 (Clubsport)
This is aimed at drivers who regularly attend trackdays but still drive the car on the road. This M135i/M140i suspension upgrades achieves greater body control, increased camber range and improved balance under sustained load.
The package includes:
- Choice of 1.5-way or 2-way adjustable coilovers
- Suspension Secrets Adjustable camber plates
- Suspension Secrets Front & rear drop links
- Suspension Secrets Solid front control arm bushes
- Suspension Secrets Adjustable rear toe arms
- Suspension Secrets Adjustable rear upper camber arms
- Suspension Secrets Rear upper third link arms
- Suspension Secrets Solid rear control arm bushes
Best For: Cars used on the road and track
Handling Pack 3 (Track)
Handling Pack 3 is for serious circuit use. This comprehensive kit removes all unwanted compliance in the M135i/M140i suspension system and provides full geometry adjustment front and rear.
The result is consistent tyre contact under heavy load and precise chassis balance at high speeds.
This package includes:
- Choice of adjustable coilovers
- Suspension Secrets Adjustable rear toe arms
- Suspension Secrets Off-centre caster control arm bushes
- H&R anti-roll bars
- Suspension Secrets Adjustable rear upper camber arms
- Suspension Secrets Rear upper third link arms
- Suspension Secrets Adjustable rear traction arms
- Suspension Secrets Solid rear control arm bushes
Best For: Driving on circuit with semi-slick and slick tyres
Full Kinematics Kit
The Suspension Secrets Full Kinematics Kit replaces the remaining compliant factory components with fully adjustable, solid-mounted arms and bushes.
Designed to work with upgraded coilovers, this kit allows full rear camber and toe control, and eliminates geometry change under load. It also increases rear stability and provides proper alignment for aggressive track settings.
The package includes:
- Suspension Secrets Adjustable rear toe arms
- Suspension Secrets Adjustable rear camber arms
- Suspension Secrets Adjustable rear traction arms
- Suspension Secrets Solid rear control arm bushes
- Suspension Secrets Solid front offset caster bushes
- Suspension Secrets Adjustable rear upper third links
Best For: The ultimate chassis upgrade for serious track drivers.
Why You Should Upgrade
The BMW F20/F21 M135i and M140i are genuinely capable cars, but the standard suspension setup holds them back when you start driving them properly. Soft factory bushes, underwhelming alignment settings, and limited camber adjustment contribute to the understeer and unsettled rear end many owners notice.
From our experience developing suspension upgrades for these cars, a proper geometry setup combined with the right performance parts makes a huge difference. Adding Suspension Secrets adjustable camber plates, solid front control arm bushes and adjustable rear toe arms removes much of the unwanted movement in the chassis and allows the suspension to do its job properly.
Once these fundamentals are sorted, the BMW F2x platform really comes alive. The steering feels clearer, the front end grips harder and the rear axle becomes far more stable – turning the M135i and M140i into the engaging driver’s cars they always had the potential to be.
See the full range of Suspension Secrets upgrades for the BMW F20/21 M135i and M140i.
