Last week we talked about how long you can run rotors after they begin cracking. The design of rotor you use plays a large role in how long they’ll last. A question I often hear is “What type of rotors should I get?”
Long story short: If smooth rotors are working for you, GREAT. If you are having one of a couple possible issues, slotted may help. Save the drilled rotors for cars-n-coffee crowd. YES, I know some supercars come with them, that doesn’t mean you should. Keep reading to find out why.
Rotors are there as a surface for the pads to do their job. There may be minute differences in pedal feel between smooth, slotted, and drilled.. but not much. If you are driving and having a problem with stopping power, rotors are the LAST place you should turn. If full braking pressure isn’t able to lock up the brakes, look at your pads. If you lock up your brakes too easily, check your tires. Brake Fade? Check your pads and brake fluid. Spongy pedal? Re-bleed the system.
The internet is full of stories like: “I know someone whose brakes worked way better with upgraded rotors!” – This may be the case if their previous pads weren’t bedded into the rotors correctly, over-torqued wheels, bad hubs, bad calipers, old fluid, or most likely: They replaced brake pads on along with the rotors. Rotors without obvious defect are VERY RARELY the cause of any issue, however an “upgrade” to a slotted or drilled is such a visual improvement that they usually end up taking all the credit.
If you are new to the track and prepping your car, you do not need to upgrade to drilled or slotted rotors.
Smooth Rotors:
Smooth rotors, or “blanks” are what the name implies, smooth. For many cars, these will do just fine on track. If you are using them without issue, continue to do so. They are also the cheapest, so replacing them in time will be less money than the alternative options.
Spec Miata racing is HARD racing, but they are admittedly very easy on brakes. With 120 horsepower and 2400lbs, they don’t work too hard (For a race car). Yet, a full season of racing and HPDE with Hawk DTC 60’s and Toyo RR’s (racing slicks) is still not easy work. Despite that- My smooth rotors hold up just fine, with just a bit of heat-checking showing after a year of events. Front rotors can last two years without issue, and rears… well… I’ll let you know when I replace them.
Slotted Rotors:
Slotted rotors are a popular choice for track and racing cars that aren’t getting what they need from smooth rotors. These are typically the faster, heavier cars where the brakes need to stop much more than a Miata. There isn’t a simple formula like you need slots if your car weighs over “X” weight and makes over “Y” power, as there are several factors… if your blank rotors are doing the job, keep them.
What do the slots do?
The slots give a place for debris to escape, avoiding unwanted pad deposits on the rotor. The largest benefit of the slots, is they wipe, clean (or shave) the pad surface which helps prevent glazing pads and unwanted deposits from building on the pad surface. However, their largest benefit is also their largest compromise as they’ll eat through pads considerably quicker than smooth rotors.
Frequently, the pulsating brake pedal most often associated with “Warped Rotors” is largely from uneven deposits of pad material on the brake rotor (Other possible causes include over torqued wheels and improperly bed brake pads). If the same feeling returns with new pads and rotors, an upgrade in pad quality may prevent it. If upgrading pads doesn’t, slots may be the answer. Slotted Rotors are a popular upgrade on track, but also have some merit with tow vehicles as the extra loads often lead to overworking the front brakes.
Drilled/ Drilled and slotted Rotors:
Do not run drilled rotors. Walk around the field of a car show and you will see plenty of cars with drilled rotors. Walk around the paddock at a racetrack and you will see smooth (blank), or slotted rotors… with maybe a few cars with drilled rotors here and there, but they are rare.
The internet is filled with a lot of mixed information about drilled rotors. The important thing is to look at WHO is saying what. Typically only bench racing forum jockeys and cheap rotor salesmen are pushing for anyone to “upgrade to” drilled rotors on a track car, or even a street car. Are there any advantages? Properly drilled rotors provide much of the same advantages of slotted. Are there disadvantages? YES. Drilled rotors are much more prone to cracking, and typically do it much sooner than their smooth and slotted counterparts.
Do drilled rotors detract from overall performance? Well, since they don’t provide any benefits over slots, but are more prone to cracking, I’d say YES.
Drilled rotors were designed over 70 years ago to help pad gasses escape under heavy braking. Modern pads do not off-gas anywhere near like they used to.
Some supercars come with drilled rotors… You can bet that they are not simply the “Drilled” option available for your Altima on Rockauto. “Real” racing rotors are incredibly expensive (and still crack sooner than their drilled or smooth counterparts). Many performance brake companies either do not sell drilled rotors, or recommend them only for customers seeing only street or minimal track use. If a rotor description spends as much (or more) time talking about the look as they do the performance, think twice before buying as a performance upgrade.
Why is the demand for drilled rotors still there? Why do some manufacturers still deliver new cars with them? In my opinion: it’s mostly for the bling factor. Rotors diameters are HUGE and getting larger, and wheels are getting more and more open… so those giant rotor faces need to be sexy to their target audience. Old habits die hard, and the general “motoring” public still expects to see holes in their rotors to “prove” how well they perform. Thankfully, we are seeing a trend of many companies moving away from drilled and towards slotted/scalloped and the like. 
For me? I’ll stick with my $17 blank rotors. These are tempting though…
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