Hot spots can be a common issue with automotive brake rotors. While they often diminish with usage, it’s crucial to pay attention to brake vibrations, as they can be an outcome of hot spotting. To minimize hot spotting, consider the following measures:

  1. Opt for a matched rotor and pad set: Not all brake pads have the same scrub factor, and various rotors are crafted from different types of iron. Ensuring compatibility between your brake pads and rotors is essential to reduce the risk of hot spots.

  2. Choose a slotted rotor with an adequate quantity of grooves or wider grooves if you prefer this type of rotor.

  3. Allow the brake pads ample time to bed in, and adhere to recommended bed-in procedures.

The concept of “scrub factor,” which involves the initial abrasion between the pad and rotor, plays a critical role in rotor health and helps clarify the rest of this discussion.

hot spots on rotors

While many people desire “low dust” brake pads, it’s essential to understand that without a specific scrub factor, your brakes won’t function correctly. Abrasion, in various forms, generates dust (a mixture of disc and pad materials). Therefore, a “no dust” pad, if it were to exist, would likely lead to hot spots and potential brake shuddering.

In the automotive market, cast iron comes in two primary grades, which are widely used in 99.5% of production cars. Although there are exceptions like ceramic or carbon ceramic rotors and non-iron race rotors, these options are typically expensive and seldom found in production vehicles, aside from a few high-end exotics. The focus here is on the prevalent use of iron in its two fundamental forms for the majority of vehicles.

G3500 High Carbon, featured in select German vehicles from the factory, is an excellent choice when used in combination with Original Equipment (OE) pads or those with a similar scrub factor. EBC, for example, employs G3500 for their SG2F race rotors.

G3500 is a pricier option but requires a matching pad with a corresponding scrub factor for a specific reason: during heavy braking, carbon can separate from the rotor, leading to the development of these troublesome hot spots. Using the right pad will swiftly resolve the issue, resulting in flawless brake performance.

Why opt for G3500?

It offers slightly superior heat absorption and crack resistance when subjected to substantial loads.

On the other hand, G3000 Normal Carbon, utilized in approximately 95% of all cars, is a highly suitable material for most vehicle brake systems. It is more straightforward to pair with various pads and is a more cost-effective option than the G3500.

The primary difference between them is quite minimal. Generally, rotors made of grey iron with less than 3.5% carbon content fall into the G3000 category, while those with over 3.5% carbon content belong to the G3500 category.

EBC best matches pad compounds for iron rotors

G3000 iron – Greenstuff, Yellowstuff and Bluestuff all have a scrub factor of 5-6 ( our internal measurement )

G3500 iron – RP1, RPX, SR11 and SR21

So when you buy non-EBC rotors check first which grade of iron you have been supplied, EBC plain, USR, GD, and BSD are all G3000, and EBC two-piece SG2F are all G3500 material.

We haven’t discussed the innovative EBC SR series sintered race pads here. These pads operate differently than conventional ones by depositing a film on the rotor and braking against that film, resulting in nearly zero rotor wear. It’s essential to note that the SR series is exclusively designed for track use, not for regular street driving, and is setting new benchmarks in the evaluation of race pads.

While there is a wealth of information available on these topics, a few important clarifications should be noted:

  • There is no such thing as “rotor warping.” Instead, issues arise from disc thickness variation caused by a rotor with excessive runout during installation, a problem that can only be rectified by resurfacing the rotor on a professional brake lathe like the Pro Cut.
  • Do not mistake hot spots for outline etching, where a pad’s outline stain may appear on the rotors after a vehicle is parked, typically in wet conditions.
  • It’s unrealistic to expect a completely dust-free brake pad. Nevertheless, EBC pads contain no steel fiber, which is present in most other pads. As a result, EBC pads generally produce less dust, making it easier to clean the dust from your wheels.

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