There are few sounds in automotivedom less pleasant than brake squeal. While increasing brake temperatures will typically alleviate squeal, keeping your Porsche's brakes at racetrack temperatures around town isn't practical. It's important to consider what is causing your Porsche's brakes to squeal, and determine whether the noise is caused by wear, or the high performance nature of your braking system. In recent years complaints about squeaky Porsche brakes have cropped up in the press. In most cases this squeal is not caused by a mechanical fault. The noise is caused instead by the construction and composition of the brakes themselves.
Causes of Porsche Brake Squeal
Every object in the universe will vibrate at a given frequency when acted upon with appropriate force. Smack a bare brake rotor with a hammer and it will ring like a gong (try it in the shop on a sleepy friend). Fastening the rotor to the braking system doesn't entirely dampen this tendency. Instead it combines the resonance of the brake rotor with the resonance of every other part in the system. When a strong enough vibration passes through one component it can transmit that vibration into other parts.
Typically squeal will originate in the brake rotor. But, the nature of the vibration will also cause the hub, caliper carrier, caliper, and other nearby parts to vibrate along with it.
The cause of this vibration is typically uneven friction across the face of the brake pad where it meets the brake rotor. During normal driving a brake pad will heat up and cool down unevenly across its surface. Depending on the intended operating range of the given pad, this can cause the pad to have a high coefficient of friction in some areas, and a lower coefficient in others. In effect the pad is repeatedly gripping and releasing the face of the brake rotor as the rotor passes across it. These high-frequency stick-slip moments cause microscopic vibrations which are then transmitted into the entire brake system.
Reducing Porsche Brake Squeal
Some measures are in place to reduce these vibrations. These include weighted dampers on the pads themselves. While these measures can negate some squeal frequencies, it is not possible or desireable to cancel out all frequencies. Unfortunately under many conditions Porsche brakes will squeal.
Unsurprisingly the issue seems to be worse in cars equipped with Porsche Carbon Ceramic Brakes. These systems are designed with higher operating temperatures in mind than their steel counterparts. Because of this, and their advanced heat-shedding properies, PCCB systems tend to squeak at lower temperatures.
Those of us who have used high performance brake pads are very aware of the pitfalls of pads designed around high operating temperatures. Many years ago I ran track pads on my Volkswagen Golf, and my car sounded like a school bus coming to a stop during normal driving. Given Porsche's requirement that their pads work both on the road and on track, it is not altogether surprising that some squeal is evident. As temperatures increase, the tendency towards squeal should lessen.
While much of this may be readily apparent to more experienced Porsche owners and car enthusiasts, it is not true for everyone. If you hear someone complaining of brake squeal in their Porsche, remind them that it may be a feature, not a bug and point them to this post to explain why.