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

"Working with BMW tuners Birds, we’re going to replace the standard, under-specified suspension with much higher-quality Bilstein components tuned specifically for the M135i, we’re going to fit a Quaife limited-slip differential and we’re going to lift power to somewhere approaching 400bhp. We might yet make a few other modifications, too..."

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