Brake Discs | Size Matters

Do different brake discs affect overall braking performance?

With so many different brands offering varying styles of performance brake discs all claiming their design is industry leading, it is becoming extremely difficult to differentiate truth from marketing when it comes to choosing your next set of replacement discs.
 
In this article we break down the main features of a brake disc, why they matter and how they affect your braking performance and longevity.
 
Heat is the biggest attribute to premature/irregular disc and pad wear resulting in thermal distortion and the various associated symptoms.
In isolation, disregarding external factors such as aftermarket brake cooling, the disc manufacturer will typically take the following aspects into consideration during design.
 

  • Material - The material of which the brake disc is cast from; its tensile strength, stability against expansion and contraction, surface hardness and other factors. This is achieved by each manufacturers' own proprietary R&D process where mixtures of additives, carbon content and iron compositions will determine the quality, stability and durability of the finished product.

  • Size - The diameter of the disc determines the brake torque generated by the calipers and pads. Increasing or decreasing the radius will change the brake torque and bias between both axles. 

  • Thermal Capacity - Determined by how much weight or mass is located in the outer ring section of the disc. This is the area where the friction surface of the disc meets the internal vanes. The more mass located in this area, the more thermal capacity a disc has.

  • Unsprung Weight - Critically affects chassis dynamics, so a calculated balance between weight reduction and thermal capacity is crucial.

  • Air Gap, Vane Design, Heat Dissipation - This is where two identically sized discs can perform at vastly different levels based on their internal designs, and usually where the differences in manufacturing costs occur. We will look at these design aspects in further detail later.

  • Slot Design - Slot depths, shapes and lengths all influence braking characteristics such as noise, initial bite, modulation, pedal release and pad/disc wear.

 
Each brand has their own strategy to market their chosen designs, however not every design will work optimally for every given application. The reasons are rarely explained accurately so the result is generalised into a blanket negative experience toward that brand entirely. A good example would be seeing a brand that values weight reduction as its key quality and fitting them to a 1000 hp, extremely front-biased RS3 road car paired with an aggressive sprint type pad. This combination is guaranteed to produce judder almost immediately as the discs struggle to cope with the amount of heat generated.
 
The air gap and vane design are crucial design components that effect disc cooling efficiency. Below is an example of how different vane designs look and function. It is important to note that designs favouring weight reduction will typically have lower thermal capacity and this is where picking the correct disc will determine the performance vs longevity.
It is essential to pick the correct disc design to suit your intended application. Heavy turbocharged vehicles will typically require high-thermal discs, even for short races or time attack style events. Please speak to us to understand which discs are fit for your purpose.
 
 
How do disc face types affect brake performance?
 

Brembo drilled disc assembly

Drilled: drilled brake discs are suitable for a wide range of applications, operating temperatures and driving environments (especially wet weather).

  • Benefit: offers the highest initial response of all the available disc face types while continuously refreshing the braking surface and being also typically a bit lighter.
  • Drawback: Drilled discs are generally more prone to heat checking and thermal cracking if used consistently at extremely high temperatures. This however, really depends on the track, driver, and chassis setup.
 
Brembo Type 1

Type-1: Brembo “8 straight – slot” face type with an emphasis on stable brake feel and improve resilience against thermal cracking.

  • Benefit: stable braking feel at all temperatures, low disc wear, and continuously refreshing the braking surface for optimum performance.
  • Drawback: The Type-1 standard disc face has the lowest “initial response” or “bite” compared to Brembo Drilled, Type-3 or Type-5 discs.

 

Brembo Type III Disc assembly

Type-3 (Aggressive Face Type): motorsport developed face type with an emphasis on high initial response while maintaining a smooth pedal release.

  • Benefit: highest overall braking confidence, control, and allows driver to spend less time on the brake pedal. When chasing the fastest lap time, less time on the brake pedal typically leads to a quicker lap time.
  • Drawback: Any disc with an aggressive face type like the Type-3 will have a higher chance to mechanically abrade the pad and disc surface leading to quicker or uneven pad wear. However, this really depends on variables such as car setup or track layout

 

Brembo Type V Disc assembly

Type-5 (Endurance Face Type): motorsport developed face type with marginally less initial response compared to the Type-3 face type. The Brembo Racing Type-5 face type was also designed to have lower pad and disc wear for certain long distance endurance races (mostly 10, 12 and 24 hour races).

  • Benefit: braking modulation and control similar to Type-3, while offering lower overall pad and disc wear on the track.
  • Drawback: While the most well balanced of all Brembo face types, Type-5 discs generally do not have as high of an initial response compared to the Type-3.

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