The BMW M135i is already a hugely capable performance hatch, combining BMW’s N55 turbocharged engine with excellent chassis balance and everyday usability. However, for owners looking to push their cars further, there are several key areas where targeted upgrades can transform reliability, handling, and driver confidence.
For this 2015 BMW M135i, we carried out a series of carefully selected upgrades designed to improve both performance and longevity, while maintaining the car’s usability on the road.
Engine Reliability Upgrades
As part of the build, we fitted a fresh set of upgraded rod bearings to provide additional peace of mind under higher load and spirited driving conditions. The N55 engine is strong, but preventative maintenance is an important consideration on performance vehicles that see hard use.
To further support the engine during enthusiastic driving, we installed a baffled sump. This helps improve oil control by reducing oil surge during heavy cornering, braking, and acceleration, helping maintain consistent oil supply when it matters most.
Improved Rear Subframe Control
One of the biggest improvements for the F20 chassis comes from reducing unwanted movement in the rear subframe.
We manufactured our own Senior Performance solid aluminium rear subframe bushes in-house, replacing the original compliant factory bushes with a much more rigid mounting solution. This creates a stronger connection between the rear subframe and chassis, improving rear-end stability, response, and overall handling precision.
By reducing subframe movement, the car feels more connected, especially during cornering, acceleration, and direction changes.
Chassis & Handling Improvements
To complement the upgraded rear subframe mounting, we fitted uprated anti-roll bars to further improve chassis balance and cornering performance.
The combination of improved subframe control and upgraded anti-roll bars gives the M135i a sharper turn-in response, reduced body roll, and a more predictable feel through corners without compromising everyday drivability.
Precision Setup with Four-Wheel String Alignment
The final stage of the build was a full four-wheel string alignment.
A performance alignment ensures the chassis is working correctly and allows us to fine-tune the vehicle’s geometry to suit the owner’s requirements, whether that’s fast road driving, occasional track use, or a balance of both.
The Finished Result
This M135i is now a more focused and capable version of an already impressive platform. With improved engine protection, a more controlled rear chassis, upgraded suspension components, and precise geometry setup, the result is a car that feels sharper, more responsive, and better prepared for performance driving.
At Senior Performance, we focus on developing upgrades that deliver genuine improvements in reliability, feel, and driver confidence — using parts that are designed, tested, and manufactured with performance in mind.
