AP Racing RadiCal Brake Kit Review

If turning laps around a circuit track or killing cones in a local parking lot is your thing, sooner or later we know you’ll be shopping for brakes. How big you decide to go is up to your budget. Or wheel diameter. Today we’re reviewing the Stillen designed AP Racing Radical brake kit. Because we had no budget, of course.

Full Disclosure: Drive TV needed a specific BMW to test brake upgrades and selected mine. I drove my personal car from Virginia to New York on my own dime to install various brake upgrades and perform braking tests at Monticello Motor Club. In exchange, I got to keep the AP Racing brake kit. Hate away.

I met up with Mike Spinelli, Producer at DriveTV and Bill Petrow owner of Broken Motorsports on a beautiful weekday morning at Monticello Motor Club, located just 90 minutes north west of The Big Apple. If you haven’t heard of a motor club before, think of a golf country club, but instead of swinging clubs you’ll be swinging laps along side a field of breath-taking machinery. But I digress.

After a full morning of repeatedly stopping distance tests with various other brake upgrade options, it was finally time to open up the Stillen boxes. We had a full four wheel AP Racing brake kit which was made up of a 6-piston, 370mm rotor up front and a 4-piston, 360mm rotor out back with stainless steel lines. I was six years old once again and this was Christmas morning.


The box lids raised and the room lit up. The 2-piece floating rotors were nothing short of art. I could not believe the awesomeness of which I was gazing upon. And then there were the calipers. Humongous. Quite literally larger than my head. And then I realized they were for the rear. Oh. My. Gawd.

Why AP Racing

Understanding what a product does and how it will effect your car before installing it is always a smart idea. So I took the liberty of calling Stillen and had a chat with resident brake expert, Eric Hayhurst. Eric explained that Stillen is the only company authorized by AP Racing to develop brake kits for street use. The kits are tested in house and are all designed to work with the factory ABS, master brake cylinder, traction control systems and retains similar front to rear brake bias – plus or minus five percent.

We’re all familiar with Brembo, but you may not have known that AP Racing is owned by Brembo and there is a big difference between the quality of AP Racing calipers and the Brembos calipers found on “population production” cars such as the Mitsubishi Evolution, Subaru STI and Ford Mustang. Sure, they’re both big and aluminium with but that’s where the similarities end. The automakers are out to save pennies, and they do it here too.

“This is race-bred technology trickled down from an environment where parts are designed to be replaced by a pit crew in seconds”

The internal routing of brake fluid and piston seals, for example, are not optimized for track use. This is why so many Brembo calipers change color after hard track use. And while better than a single piston sliding caliper, fixed position Brembo calipers can flex like body builder. Watch this video to see for yourself. This is important because a caliper that flexes and deforms will drag a pad across the rotor. And brake drag costs power and economy. We don’t like drag.

Now let’s look at the rotors. The fronts are 370 x 36mm, 2-piece floating design utilizing aluminium hats and replaceable iron discs. Did you catch that number, 36mm? These are the Liberty Walks of brake kits. The thicker disc surface ultimately translates to increased thermal capacity. 48 cooling veins mean maximizing heat dissipation which lets the brakes operate consistently at lower temperatures. It’s all part of what AP Racing calls WDT, or Wide Disc Technology.

AP Racing J Hook Rotors
And the discs aren’t blank. They aren’t drilled and they aren’t slotted. Well, they’re kind of a curved slotted. It’s called a J-Hook – the same design used on Le Mans race cars.

What makes the J-Hook rotor superior to slotted or drilled methods of cooling? A slotted rotor has what, 6 to 8 grooves and in between is blank iron. As the rotor heats up, those iron portions are expanding and at a different rate than the cool slots. With the offset J-Hook design, there are no large iron patches. Heat distributed much more efficiently. The J-Hook also has an advantage when it comes to cleaning the pad face. The 45-degree J hooks wipes the pad surface clean and effectively throws the debris out. The leading J-Hook edge also increases friction as it bites the pad.

The components in this kit are quit literally race quality and developed to take the punishment of the track so you can focus on pushing your street car to the limits lap after lap. Far beyond what the capabilities of any track-oriented factory brake systems. They’re made to maximize thermal capacity and distribute race condition levels of heat without breaking a sweat. You’ll find AP Racing in Formula 1, Le Mans, NASCAR and on the fastest production hyper cars in the world.



There I was. Hard parking on stilts in the depths spacious garage bay of the Monticello Motor Club with my own pit crew. Cars were screaming down the front straight just outside but the only thing racing was my heart as my eyes gazed upon this most pulchritudinous of functional upgrades.

Installation of the entire four wheel brake kit was butter. With two mechanics, we clocked just about 30 minutes to mount the new hardware and bleeding of the lines just another 5 minutes or so. Seriously, folks, it’ll take longer to remove your original brake hardware than to install the AP Racing kit. Remember, this is race-bred technology, trickled down from an environment where parts are designed to be replaced by a pit crew in seconds, not minutes.

Wait, are these things even going to fit? 370mm rotors are huge but the calipers also take up a lot of space. If any wheel was going to clear these large calipers it would be a set of Volk racing wheels, right? Luckily the Volk TE37 wheels had just enough clearance!

Do we really have hide these behind a set of Volk wheels? When’s the last time you heard that? “Take those forged wheels off, I want to see the stopping hardware!”, said no hard parker, ever. Until now.

Measurable Performance

As ridiculous as this kit looks sitting behind the Volk wheels, performance on the track is nothing short of awe inspiring. Just a week prior I was turning laps at New Jersey Motorsports Park and can tell the world first hand how the factory brakes are good for about 2 laps. The warm-up lap and the first time getting hard on the brakes slowing the car down from 118 MPH on the front straight. It was at that specific moment that the wimpy factory brakes gave up the ghost.

Fast forward to today. Pro racers Spencer Cox of Speed Sport Tuning had just bed in the brakes of the freshly installed Stillen designed AP Racing big brake kit and was once again out on track, this time in a session chasing Porsche Cayman GT3’s. He returned to the paddock with great praise of power and consistency.

Testing, testing.

A photo posted by Mike Spinelli (@mikespinelli) on

Then it was time to head out to measure braking distances from various speeds. To do so, our test vehicle would reach 60 MPH just before the braking zone, make an emergency stop, then quickly circle back and repeat.

In factory trim, our 2012 BMW 328i stopped from 60 MPH in just 86 feet but that distance quickly expanded to well over 90 ft after just a handful of back-to-back stops. This is exactly what we expected. The only way to keep those distances consistent is to lower braking temperatures.

And that’s the entire point of any brake upgrade. The trick is keeping those temperatures as low as possible under the most strenuous of race conditions.

The AP Racing brake kit not only stopped my car a few feet shorter than the factory brakes, but braking distance was within inches of the shortest distance in every back-to-back test. Dozens of stops were performed. Look for the episode on Drive TV. It’s coming soon, I promise.

End Game

Investing in a big brake kit is not cheap. A kit like this MSRP’s for over $7,000. Many, many replacement rotors and pads could be purchased before a kit like this saves the average weekend warrior any money at the track. Nonetheless, at some point the limits of smaller brake “upgrades” will be reached and the only way to go faster is to brake harder. When that time comes, you might as well go with a proven source.

Technical Specifications

Application Front Rear
Rotor Size 370x36mm 360x28mm
Rotor Design 2-Piece 2-Piece
Disc Design J-Hook J-Hook
Rotor Hat Aluminium Aluminium
Caliper Size 6 Piston 4 Piston
Pad Shape D70 D55

Bonus Images




  1. Question for you – I am considering these as a brake upgrade for my car. You mention D70 pad shape, but I haven’t been able to find much pad selection here. Thus far, Stillen has mentioned Ferodo DS2500 and DS3000 as the only options. Have you had any luck finding any others?

    1. Hey Shaun! I haven’t looked at other pad options primarily because the Ferodo DS2500’s that come with the kit are superb although they do dust a lot. Do you have the same car by chance? I’ll comment or maybe update the post when if I find pad alternatives.

      1. Thanks Josh, appreciate the input. The DS2500’s have been holding up well through track use?
        I havent tried DS2500s but I was concerned about the lack of pad selection. Seems like these calipers have been around for at least 2 years but only Ferodo supports the caliper (with 2 pads only, no less!).

        I do not have the same car…but similar! Audi S4.

        1. I’ve ran Ferodo DS2500 pads in many of my previous dual duty cars at HPDEs and Time Attack. Never had a complaint other than dusting so I was pleased to hear they came with the AP kit.

          BTW, I just called Winmax and they have pads available but they aren’t in their online catalog because it’s a real race application. No doubt the other guys do too.

          1. Thanks for the info, Josh. That’s reassuring.
            Out of curiosity, do you know the piston sizes they spec’d on the calipers which came on your car? On the AP racing website, I’m able to find these under the “World Radi-cal” section, however, the specs for these all show that the 6 piston variants are intended for a 380mm rotor or greater. I can’t find the exact ones that will mate to a 370mm, and as a result, I’m not able to find piston area info!

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