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Behind the Speed: StopTech Big Brake Kit

Project 335i gets some massive stoppers

Behind the Speed: StopTech Big Brake Kit

Project 335i has seen major upgrades in almost every area, and up until the recent heavy track days, it’s been pretty well balanced on all accounts. However, with 140mph straightaways and 20-minute track sessions, the E90’s factory brakes were struggling like a T-28 Soviet tank at Le Mans. Confidence is key when it comes to lap times, and if there’s one thing that kills confidence, it’s no brakes into The Corkscrew, just a foot off a GT3s bumper.




With the seats folded down, the 335i was packed with boxes as we continued our journey south from LA to visit our buddies at European Auto Source (EAS), in Anaheim. Steve and Tom at EAS are like family at this point, since we worked together on my last project, a 650hp E46 M3, and I’ve shot plenty of their insane builds over the years. They’re no strangers to the track prep hustle dance, either, nor do they ever skip a bit with their BMW prowess and keen attention to detail.


We started by emptying each box and I couldn’t help but organize the kit in my typical OCD fashion. Once the factory brakes were off, the install was a breeze and went without a hitch, which meant I had time to ogle at the sheer beauty of this kit and appreciate the quality you get when you go with StopTech. I mean, just look at those calipers!




So, what’s in the box?


The 335i kit is offered with an ST60 6-piston front caliper on either a 380x32mm or 355x32mm rotor. Running something as large as the 380 would lock us into using 19” wheels, so we opted for the smaller 355mm discs that’ll fit behind 18’s. Out back, we have an ST40 4-piston caliper on a 345x28mm rotor.  StopTech’s rotors are dubbed AeroRotors, and ours are slotted, but they’re offered cross-drilled and zinc-coated as well. These rotors are patented with curved, airfoil-shaped vanes and an air channel between the discs that widens at the trailing edge of the vanes. The aluminum AeroHats are lighter and have directional stand-offs between the rotor and mounting hat that increase airflow to the hotter (outside) face of the rotor by 15%. This pattern is meant to keep the rotor cool as it spins at speed, exhausting hot air with every rotation.


Each kit comes with application-specific hard-anodized 6061-T6-billet aluminum mounting brackets with stainless steel studs. The studs and set screws offer strength and durability, but most of all, since they’re specific to each application, precise and proper fitment is guaranteed, and likewise, so is an easy installation.


Being that the 335i isn’t a full track car, we haven’t done anything with brake ducting yet, and truthfully, the design of StopTech’s rotors do a hell of a job keeping the brakes cool, providing consistent performance on track. Ask me how I know!




The hero of this kit is no doubt the 6-piston ST60 caliper in all its massive glory. StopTech offers some of the stiffest calipers on the market with their two-piece modular design, even stiffer than some single-piece monobloc calipers, they claim. What this means for you, though, is that the brake pads are applied to the rotors evenly, thanks to how rigid the caliper is. Paired with the included stainless steel brake lines, stable and predictable braking with a firm pedal is what you’ll get, and that means you’ll be more confident than ever before.  


While externally, StopTech’s caliper line looks the same, internally they are application specific as well. Each caliper has specific piston sizes matched to the car’s master cylinder for optimum brake balance, and each piston has high-temp silicone brake boots that’ll hold up on track. This isn’t all a sales pitch, either; we sat down with StopTech’s Lead Engineer, Tyler Hauptman, to hear more on what sets these stompers apart.


“I think StopTech stands alone in how we test our product,” he said, “We test every brake kit dynamically in 40-0, 60-0, 100-0 mph tests and also perform J-turn tests to see how well our brakes maintain stability of the car, factoring in ABS interaction during brake application and while cornering.” Think about that for a minute… StopTech produces brake kits for over 25 different manufacturers, ranging from current generation models all the way back to 60’s 911s, and they test every one.



“We don't release a system unless it performs better than stock,” said Tyler, “We also have three brake dynos and a friction lab with a group of dedicated test engineers that gather huge amounts of data all day, everyday. All of this testing and wealth of data gives us a deep understanding of everything brakes. We have a good grasp on all the mechanisms, metallurgy, and design that makes brakes perform better,” Tyler explained. “This is why I have been here for 6 years; I 100% believe in the product.”


I’m inclined to believe him, and the proof is in the lap times. They stayed mostly within a second of one another for twenty minutes straight. The brakes just wouldn’t give up an ounce of stopping power, and paired with StopTech’s own SR33 race pads, fade was nonexistent. They were so good, so unfathomably responsive, that I found myself braking too early for most turns. Sure, Laguna Seca was pretty new to me, and so were track pads, but having this much braking ability does a number on your brain when you’re so trained to expect poor performance and wild inconsistencies, lap after lap.




StopTech’s new line of racing brake pads compliments the rest of their lineup without a doubt. The pads are engineered to provide the absolute maximum levels of friction for shorter stops, increased control through superior pedal modulation and resistance to extreme racing temperatures. Currently, they offer four compounds: SR30, SR32, SR33 and SR44. BimmerWorld suggested the SR33 compound which fall somewhere in the middle with a medium friction level and a flat torque curve with temperature rise; the pads were flat out amazing. With no prior experience in the department, I can’t say I needed anything less or more – the pads were flat out amazing. They do get LOUD, of course, and we’d never suggest running them on the street unless stopping unnecessarily short and squealing like a city bus is your thing. Of course the BBK comes standard with StopTech’s Sport pads as well, which are great for spirited driving, Autocross, light track duty and the daily grind alike. Thanks to the easily removable center bridge, pad changes take about 5 minutes a caliper – insane.


StopTechs at all four corners led us to a 2nd place finish in a field of 22 with a best lap of 1:46.2. Our project 335i has a full interior, stock seats that sent me flying into the center console and door a few times, and weighs over 3600lbs. Safe to say, the brakes are taken care of and now match the rest of the car’s performance, leaving us on a quest to find proper race buckets and some much-needed weight reduction in the future, and I suppose some more seat time and driver improvement could be helpful too.


Special Thanks To:



European Auto Source

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