I DON’T USUALLY write technical articles because I’m not a mechanic or an engineer. Nor do I pretend to be one on the Interwebs, though many people do. I find some of the forums frustrating as car owners are always trying to reinforce their purchase decisions, rather than providing useful information for others. So please research your decisions, as anything I say here is just my opinion supported by experience. If you want to go faster and feel safe doing it, the first thing you should do is optimize your brakes.
Brakes are a simple device with a singular purpose, yet we are always trying to defeat them. We add larger wheels and tires, create more heat by late braking, throw in more horsepower than they were designed to arrest and then complain when the pedal turns to mush. The largest and heaviest component is obviously the brake rotor.
Brake rotors come in four variations. Vented and non-vented refer to the space between the rotor faces. The vented rotor, supplied on modern Porsches, allows cooling air to pass between the two rotor faces to reduce the operating temperature and allow more friction and grip without cooking the brake and hydraulic fluid. A further improvement to a vented rotor is a directional one whose vents are curved so the air moves more efficiently in the correct direction. These are most often found on the front where the most heat is generated. The next type is the solid-faced rotor which came as stock on older Porsches. This is a smooth-surfaced rotor that mates with the pads and works well on lower-horsepower cars. The pad wear is even and the stopping power consistent. The downside of a solid-faced rotor is that water and the off-gasses from the pad compound get between the surfaces. That prevents a quick aggressive feel to the pedal.
Now we get to the modern evolution of rotors. To eliminate the off-gasses and moisture, more performance-oriented braking systems started cross-drilling the rotor. The idea being that the off-gasses and moisture could escape the pad surface through the holes and make the pedal’s feel firmer and offer more abrupt deceleration. They are also perceived to look aggressive and sporty. This is a notion that is delaying brake-rotor progress. Things have changed but manufacturers seem stuck with the image that they’ve created and are still installing cross-drilled rotors on all their sports cars.
Here are the downsides of a cross-drilled rotor. Modern brake-pad compounds don’t create off-gasses so the reason behind the holes is gone. The holes cause uneven cooling of the metal and as a result they generate stress cracks. A cross-drilled rotor develops an uneven surface and lowers the replacement pad’s ability to seat on a half-used rotor without wasting the first 25 percent of the pad. Cross-drilling reduces the amount of surface area that the pad bites against to slow down. They effectively make your rotor smaller. The holes plug up with brake dust and render themselves useless if aggressive pads are used.
To my mind, the best lapping rotor for the track is a directionally vented and minimally slotted, mated with a medium-compound pad and high-heat (600 degree) brake fluid.
The response to these issues is a minimally slotted rotor. A slotted rotor with just a few slots cleans the pads, allows any trapped moisture or debris to escape, and still gives lots of contact area. It cools more evenly, allows for even pad wear, and doesn’t destroy the replacement pads. To my mind, the best lapping rotor for the track is a directionally vented and minimally slotted, mated with a medium-compound pad and high-heat (600 degree) brake fluid.
Of course, one can reduce some rotational mass by adding a multi-piece rotor with aluminum hat, and increase stopping power with a very aggressive pad, but now we are talking about a much larger budget for one extra lap per session. I’m not a fan of throwing money away, even if you are.
You may have noted that I suggest a medium-compound brake pad for lapping use. The reason is entirely economic. The car stops due to the friction between the pad and the rotor. While a more aggressive pad bites into the rotor harder and increases the coefficient of friction, it also chews up a rotor. Can’t have it both ways. Either increase pad and rotor wear or moderate pad and rotor wear. It’s entirely up to the driver how much braking they are willing to pay for. In the leisure sport of performance driving, we don’t collect winnings or trophies, so those last few seconds only matter to the individual driver. Any good quality pad, including the OEM ones, satisfies lapping needs.
You probably noticed at the beginning of my brake-rotor diatribe I stated if you want to go faster you should optimize your brakes. Part of what we teach is threshold braking prior to turn-in at each corner. On a 10-corner track like Canadian Tire Motorsport Park (Mosport) just being able to brake one half-second later, while maintaining the car’s stability, increases progress by five seconds. That improvement can only be maintained over a full-run session with proper use and cooling. I checked Pelican Parts and the difference in cost between the Zimmermann cross-drilled rotors and the Sebro slotted ones is only four bucks for my car.
Still not convinced? Look at any Formula 1 or Indy Car brake rotor and you won’t find a cross-drilled one anywhere. I know they hire people smarter than me.
See you all soon! </>
Photos by Adrian Chan.