Stoptech ST60 Big Brake Kit Initial Impressions and Installation Tips
Stoptech big brake kit offers plug-and-play braking performance upgrade.
When it comes to track cars, there are a few upgrades that most everyone will want to eventually work on. Most people start with a dedicated set of track wheels and tires. After all, those nice, sticky tires aren’t exactly daily driver material, and, vice versa, daily driver tires usually aren’t great on track. Then there are braking upgrades. Some cars come from the factory with fancy multi-piston brake calipers and large, vented rotors. These factory big brake kits are usually talked about in the forums as the end all be all, or the best OEM upgrade to get, if you have a less potent model.
Interestingly, my car, a BMW 135i, is one of those aforementioned cars with a ‘factory big brake kit.’ The front braking setup is a semi-floating, vented rotor and a six-piston caliper, designed by Brembo. The rear braking system is also a vented rotor, though, with a two-piston brake caliper setup. That sounds great, at least, on paper. In the real world, however, this package leaves a lot to be desired, especially in a track day scenario.
Breaking down the 135i OEM ‘BBK’
Those vented rotors look big, but are actually only large in diameter. Rotors are measured by overall diameter and in thickness, and the OEM 135i rotors are rather narrow. That means that, as a heat sink, which is what rotors are, they can only handle and evacuate so much heat. When the rotors get scorching hot, so do the brake pads, and, in turn, so does the brake fluid. Boiled-over brake fluid means an ineffective brake pedal, and a possible code brown scenario on the race track when the car doesn’t slow down in time.
Then there are the calipers. While the six-piston design looks promising, the real world effect can be devastating. 135i owners who track their cars eventually experience caliper piston failure. The piston faces chip away due to the poor heat management, which is exacerbated by the thin rotors. Once the piston faces chip away enough, the calipers eventually leak. Needless to say, stomping on the brake pedal at 150 MPH approaching a corner, and watching it go to the floor as brake fluid explodes out of the wheel well is what industry experts call ‘not good.’
Oh, and did I mention that the 135i OEM front caliper uses a bespoke brake pad design? Since no other caliper shares this pad shape, brake pad selection is limited, and expensive.
After campaigning the car for several years with constant braking issues, I gave up on the OEM brakes. Even with good pads, fluid, some ducting, and an expensive caliper rebuild kit promising a fix, the inconsistency of the factory brakes made lapping the car feel dangerous.
Continue reading about the Stoptech ST60 big brake kit.