Upgrading Your Brake Rotors

Upgrading your brake rotors. This is an upgrade that can be exciting to your Subaru especially if you’re making decent power, or if you have worn or warped rotors that are causing a vibration during braking. As you can see on our website, you will see many brake rotor options that have slotted grooves, drilled holes, or a combination of the two. Most of you will know the purpose of cross-drilled or slotted rotors, but for those inquiring minds in a nutshell, drilled holes or slots on the brake rotors are designed to combat heat. But the function stretches a little further than cooling, there is a performance advantage as well especially if you enjoy weekend SCCA or local sanctioned track events, or if you have a track-dedicated race car then 99% of the time you will have drilled or slotted rotors.

 

HOW HEAT CAN CAUSE BRAKE FAILURE – ESPECIALLY IN MOTORSPORTS

In reality, there isn’t a shelf life with brake rotors. Some people will drive their cars for a decade without replacing their rotors, and it could be that they only commute within their own town limits, lack of commuting in general, or simply neglect. Not everyone is a ‘car person’, and for those who are not, many don’t even know the difference between their engine and transmission and will only see a mechanic once they hear metal to metal noises while braking. But for those of us enthusiasts who are acutely aware about the maintenance of their vehicles in terms of what oil type we use, the turbo size, spark plug gap, we also overprepare especially if there is a weekend track day coming up. Now with autocrossing, your car is racing through a large parking lot dodging cones, and you are running the car at lower speeds because you typically never click into fourth gear, and if you get into third gear, it’s only for a few brief seconds. When you are done making your run, you can go back to your parking spot, adjust air pressure, and allow your engine to cool.

Now when you are racing at an amateur track day, an open track day, a club race event, NASA, HPDE, or other sanctioned events where you are on a racetrack, this is where your brakes will really get cooking. While prepping for these types of events, many who properly prepare their vehicles will change all fluids with the exception of power steering. The oil needs to be fresh, coolant can be flushed to make sure there is no internal debris, and the key fluid is making sure your brakes are bled with fresh performance brake fluid with a higher boiling point. In these types of track events, there are many mechanical fail points that can happen to your engine, but especially your brakes. These fail points have one common denominator, and that is heat. So, let’s discuss two key failure points in your braking system due to heat:

 

BRAKE FADE

What is brake fade? Brake fade is where you are on the brakes for a prolonged period, and your rotors will get so blazing hot that your brake pads will melt material over the discs, which prevents friction. Your rotors will be glazed over with a film of brake pad so that you could literally lose your braking function. When does brake fade happen in normal driving situations? If you’re driving through a mountain pass, and you see signs directing to a “Runaway Ramp”  for 18-wheelers and semi-trucks, this means that these units hauling heavy loads are highly susceptible to brake fade due to the weight. Because the heavier your vehicle, the harder it will be on brakes.

 

 

Now this example applies to just about any vehicle. Prolonged braking while traveling downhill without utilizing your lower gears on a manual or automatic transmission to help engine brake will result in brake fade. The same science applies to racing, because we are frequently braking during higher speeds, thus allowing the temperatures in our rotors and pads to climb very quickly. Here is an example of brake fade at a weekend track day:

 

 

LOSING YOUR BRAKES COMPLETELY DUE TO BOILING BRAKE FLUID

This instance is more prevalent than brake fade mainly in track conditions. You will almost never at any moment in time, get your brake fluid so hot that you are boiling your fluid in normal commuting, unless you are traveling downhill for miles after reaching the crest of a mountain pass. Then in that case, it’s very possible. But while going to work or getting groceries, this will never happen. Now in racing, it happens often, and this is the reason why for those who participate in weekend track events, bleeding brakes with fresh fluid is always on top of the checklist. Track enthusiasts will always use a high-temp racing brake fluid because losing your brakes while at the track is deadly.

CLICK HERE FOR ALL BRAKE FLUID

The danger with boiling brake fluid is that it creates air within the hydraulic system. Air inside the brake lines means that your brake pedal will go to the floor. When this happens, racers have no other choice than to save their car to the best of their abilities to avoid any sort of impact. Because of these reasons especially for dedicated race cars, this is why owners or crew chiefs will make sure that there is fresh fluid bled within in the system before any race to avoid any chance of moisture, corrosion, or air from a previous race.

 

 

HOW DRILLED AND SLOTTED ROTORS HELP FIGHT AGAINST HEAT

Centric Premium OE-Style Cross Drilled Front Rotors 2018-2021 STI

 

Take these cross-drilled rotors for example. The drilled holes on the rotors serve 2 key functions. One of which is to help vent the hot brake gases into the vanes of the rotor. The vanes are the vented slots in the middle of the rotor, and in many cases, these vanes are directional. The drilled holes in the rotor also collect brake pad residue which will also shoot both heat and dust out of the rotor vanes. If you have drilled or slotted rotors for that matter, and if you remove your wheel just after a track day, many times you can see a black ring inside your inner wheel barrel and that is hot brake pad residue that your rotor vanes have expelled.

The ’argument’ about cross-drilled rotors is that they are more prone to cracking. And yes, this is true because you have a vented disc that has holes drilled through it which will affect the overall structural rigidity of the rotor. But this is more prevalent in dedicated race cars because they are constantly stopping a 2-4k lb. vehicle at higher speeds, and they are perpetually hot.

Bottom line, if you decide to purchase cross-drilled rotors, don’t cheap out on them by getting cheaply mass-produced units online (yeah we know we’re an online business we talking about online auction sites). Get yourself a set of rotors made from an established brand that has been tested and has stringent manufacturing methods. We have examples like above, that are great for daily driver and weekend track events, and we have examples from Brembo that can endure the stress and heat associated with racing.

 

DBA 4000 Series T-Slotted Front Brake Rotor Single 2004-2017 STI

Slotted rotors have the same function as drilled rotors but handle heat in a different design. The slots will collect both heat and brake pad residue in the slots, where the slots will sling the hot gases and pad dust out so that your brake pad always has a clean contact surface with the rotor.

Compared to cross-drilled rotors, slotted rotors do have a little better structure because there are not holes drilled all the way through. However, the slots are bore prone to wearing down especially if you are frequently performing heavy braking after high speeds which should only be done at the track.

 

Stoptech Drilled and Slotted Rear Rotors Pair 2008-2017 STI

Drilled and slotted rotors are for those who want the ultimate in cooling efficiency during high-performance driving conditions. When these rotors are paired with a brake pad that can withstand more heat, you will always get a nice caliper bite during braking.

 

DBA 5000 Series 2-Piece Drilled and Slotted Rotors Front 2015-2017 STI

Now 2-piece rotors are mainly included in aftermarket big brake kits where you have a larger 6-piston caliper. With 2-piece rotors, you have the rotor hat which is the inside piece where your bolt holes are that attach to your knuckle. Then you have the outer ring rotor itself that bolts to the rotor hat. The purpose of this design is that it is lighter to reduce rotational mass of the wheel. With heavier larger brake calipers, it makes up for the weight, and there are aftermarket examples like the DBA units pictured above that are direct replacements for your OEM units that are lighter and are drilled and slotted to provide you with the best braking performance and fight against heat in performance driving conditions.

 

 

CLICK HERE FOR ALL BRAKE ROTORS

 

 

THE IMPORTANCE OF PAIRING YOUR BRAKE ROTORS WITH THE RIGHT BRAKE PAD

For novices out there, this is where you need to pay attention. Because we carry all of the performance brake pad options. You could absolutely overdo it or underdo it. Take these brake pads for example:

 

Carbotech XP10 Front Brake Pads 2018-2021 STI

 

These are Carbotech’s XP-10 brake pads, and these are track-only. So, if you make “because racecar” your entire personality on your daily driver, you’re going to be really disappointed when trying to brake especially in the cold weather. Race-only brake pads are designed to withstand extremely higher temperatures than normal brake pads. This means that they are much harder in terms of mass, and they won’t actually work until they get some good heat in them. When watching a race on TV, you will notice race cars driving and swerving back and forth during the warmup lap before they get the green flag. What is happening is that drivers are getting heat in their tires, so they have grip on when they come blasting into the first turn. But more importantly, they are getting heat inside their brake pads so that they will have that good first initial bite when coming to a stop.

If you have track-only brake pads on your bone stock 2023 WRX, and you get out of your driveway or parking spot, when you approach the stop sign even at 25 mph, your car will not have that initial bite, and it will feel as if you have bricks as brake pads as you roll passed the stop sign.  This is because the pad material will need heat in them before they can even work properly, and they usually need a lot of heat.

The same applies to race cars that try to use a street or daily driver brake pad. Because of the constant heavy braking during higher speeds, race cars would cook street pads very quickly, or experience brake fade as the material melts over the rotor.

And then you have another spectrum, where enthusiasts build 800-1500+ HP cars with fully built forged motors, billet main caps, giant turbochargers running 40lbs of boost, and they do back-to-back highway pulls, or if they race in sanctioned roll racing or standing mile events and try to strop at 170+ MPH on Amazon or Autozone brake pads, this will lead to boiling brake fluid or brake fade really quickly. This is why it is important to think about what brake pads will work the best with how you use and how you drive your car. Here are some examples:

 

DAILY BRAKE PAD:

Stoptech PosiQuiet Semi-Metallic Brake Pads Front 2004-2017 STI

 

STREET AND TRACK BRAKE PAD:

EBC Yellowstuff Street and Track Brake Pads Front 2015-2021 WRX

 

TRACK ONLY BRAKE PAD:

DBA XP650 Track Performance Front Brake Pads 2004-2017 STI

 

CLICK HERE FOR ALL BRAKE PAD OPTIONS

 

 

REMEMBER, BE SENSIBLE WITH YOUR ROTOR UPGRADE

The good thing about cross-drilled, slotted, or the combination of the two when it comes to upgrading your brake rotors, is that yes, they are streetable. We have several performance street pad options that will pair greatly with any rotor option you choose, and it will give you better stopping performance on the street, and for the occasional track day. If you have a dedicated race car, then you are most likely well-versed in brake knowledge, and know exactly what to get. So, make sure you have good rotors, get yourself a good set of pads, make sure you get a proper brake fluid. Lastly while you’re upgrading rotors, look into upgrading your brake lines with braided stainless-steel units. These will not expand under pressure and will improve the braking response especially from the brake pedal to the caliper.

 

CLICK HERE FOR ALL SS BRAKE LINES