Brake Literature

Brake Literature/DISC Literature

What is residual stress?

residual stress

Residual stress is a structural weakness that occurs in the casting process of iron, the main material used in brake discs.

During normal street-use, residual stress does not cause any problems with the discs. When the discs are used at race circuits at high temperature conditions for an extensive of time, the residual stresses within the disc can lead to thermal cracking and deformation. The heat treatment process relieves the residual stresses to prevent thermal cracking and deformation from occurring.

Comparison chart of the performance difference of a heat treated disc and non-heat treated disc
    non-heat treated disc heat treated disc
Crack resistance When a one-make series Honda DC5 Integra is driven at 2min 10sec/lap on the Motegi race circuit Hairline cracks occur on the braking surface after 1 hour of use. Hairline cracks occur on the braking surface after 2 hours of use.
When an street legal Honda DC5 Integra is driven at 2min 20sec/lap on Motegi race circuit Hairline cracks occur on the braking surface after 2 hours of use. Hairline cracks occur on the braking surface after 5 hours of use.
Judder resistance When a one-make series Honda DC5 Integra is driven at 2min 10sec/lap on the Motegi race circuit Minor juddering (vibrations) occur after 1 hours of use. Minor juddering (vibrations) occur after 2 hours of use.
When an street legal Honda DC5 Integra is driven at 2min 20sec/lap on Motegi race circuit Minor juddering (vibrations) occur after 2 hours of use. No juddering (vibrations) occur after 4 hours of use.
  • ※The comparison test above was done using a non-heat treated disc by another manufacturer and our heat treated HD disc. The R01 brake pads were used for both tests.
  • ※All of the testing above was done on the Twin Ring Motegi race circuit.
  • ※The data values above can vary depending on the conditions (weather, pads used, vehicle set-up, driver, lap time).
  • ※The data values should only be used as a reference to better understand the performance differences.
What is Heat treatment process?

■the temperature changes in the heat
treatment(imaginary figures)

At DIXCEL, a strict temperature control is implicated at each step of the heat treatment process.
The details of the time and temperatures of the heat treatment process cannot be disclosed, so hypothetical values will be used to explain the heat treatment process.

First, the temperature is increased by 5 degrees centigrade every 10 minutes. When the temperature reaches 300 degrees centigrade, the temperature is kept the same for 8 hours.
Next, the discs are cooled by temperature being lowered by 5 degrees centigrade every 10 minutes. The graph on the left shows that the temperature control is very ideal.

The whole heat treatment process is completed over a period of 24 hours. This allows for slow and gradual process under perfect humidity control.
This helps prevent deformation, strengthens the bonds between the molecules, and allows for an increase in heat resistance.
※The temperatures and times listed in this explanation are hypothetical values. The actual temperatures and times that DIXCEL uses are different.

When driving on a race circuit, the benefits of brake discs with slots and/or heat treatment.

The advantage of having using the slotted disc is an increase in stopping power. The advantage of the heat treated disc is an increase in durability.
For the slotted discs, our testing results showed an average braking power increase of 15-20 percent. The heat treated discs have better protection against thermal cracking, juddering, and distortion.
They also increase the life of both the pad and disc. For users who want best of both worlds, DIXCEL recommends the FS or HS series discs.

Brake Disc Material

Cast iron and carbon are the two main materials used to make a brake disc. The benefit of Carbon is that it has a high thermal resistance and is lightweight. The downside is that Carbon is expensive, so it is used mainly by high budget racing teams. Cast iron is the more commonly used base material. There are three types of cast iron, each type has different graphite composition; grey cast iron, CV cast iron and ductile cast iron. Grey cast iron (flakes graphite cast iron) has excellent processibility and anti-abrasion capability. Grey cast iron has the advantage of being easily mass-produced, making it the most commonly used by discs manufacturers. The drawback is that it could be deformed or cracked under repeated sharp changes in temperature in the high temperature range (about 800℃). Ductile cast iron is an excellent material. The tensile strength of ductile cast iron is equal to that of steel. Ductile cast iron also has an high anti-heat capacity (stability against expansion and contraction). Unfortunately, it has low surface hardness, which can cause abnormal wear and/or abnormal heating due to its high exothermicity, if the material is used for brake discs. CV cast iron (Compact Vermicular cast iron) has an intermediate character between grey cast iron and ductile cast iron. The quality control of CV cast iron during the manufacturing process is extremely difficult, so the quality varies. Sometimes its closer to grey cast iron but other times is closer to ductile cast iron. After extensive testing, grey cast iron with special additives are being used in DIXCEL brake discs. OEM Products often use grey cast iron with FC150〜200 (FC is numeric representation of the strength of cast iron). DIXCEL uses grey cast iron with FC200〜250 for higher durability. After extensive research and development, DIXCEL developed a disc which has special additives to strengthen the disc's vulnerability to sharp temperature changes in the high temperature range. The superior precision and balance of the disc goes without saying.

The structure and the shape of a brake disc

The two most popular types of brake discs are solid and ventilated discs. Ventilated discs have cooling vanes between the braking surfaces which allows air to flow through, and has a cooling effect on the disc. More cars are becoming equipped with ventilated disc on the front brakes, and high-performance cars have ventilated discs on the front & rear.

  • ■Solid disc Solid disc
  • ■Ventilated disc Ventilated disc
  • Straight fin
    Number of fin being 24-48 as standard
    Less number of fin → light weight
    More number of fin → higher rigidity

    Straight fin

  • curved vane fin
    Swirl form able to exhaust cooling air to outside smoothly

    curved vane fin

  • Pillar type fin
    Less obstruction for wind for smoothness

    Pillar type fin

The precision machining of brake discs

Brake disc engineering involves the precision procedures Disc Thickness Variation (DTV), run-out, Mounting Surface Flatness (MSF), friction surface parallelism, and balance.

DTV・・・Disc Thickness Variation
Disc Thickness Variation is a measure to see if there are any variation in brake disc thickness along the entire braking surface. DIXCEL tolerance is ±1/100mm
Run-out is a test to see if the disc will spin without any vibration. The parallelism of the mounting surface and the outer friction surface is measured. DIXCEL tolerance is ±5/100mm.
  • Run out1Run out
  • Run out2MSF
    (Mounting Surface Flatness)
  • Run out3Friction Surface parallelism
MSF (Mounting Surface Flatness)
This is a measurement to make sure the disc will not vibrate after installation on the car. The flatness of the disc mounting surface is measured, and DIXCEL tolerance is ±5/100mm.
Friction Surface Parallelism
Friction surface parallelism is a check to see if the two friction surfaces are parallel. The parallelism is check on the entire friction surface. DIXCEL tolerance is ±2/100mm
The balance is to check if the weight balance of the disc is evenly distributed. If there is an uneven distribution of weight, it can cause unwanted vibrations. The uneven balanced is fixed by adding balance weight or shaving off excess weight.

f any of the precision machining standards are not met, the risk of a disc developing juddering will be high. On top of the five precision machining standards, the friction surface of the disc is machined to improve the bedding process of the new brake pads, and provides more stable braking from initial use. The groove between the mounting surface and the friction surface of the disc is designed to optimize the cooling effect, which will prevent thermal cracking and distortion. At DIXCEL, we put all discs through a thorough final product inspection. Be rest assured our products are of the highest quality.

Bedding-in of the Brake Pads
■Street use only
It depends on combination of pads and conditions of road you drive on, it takes roughly 300km〜1,000km of running-in on ordinary roads. During that period, please refrain from fast or abrupt driving or do not drive in a way as to force the temperature up. Running in of rotors will be completed simply via normal driving.
■Circuit use
istortion or cracks in rotors happen easier if optimum driving on a circuit is conducted straight from the beginning this in turn causes judders. When using a new rotor for the first time on a circuit, start with 50% braking for about 5 minutes and then go back to the pit once and take at least 5 minutes interval. After that, repeat 70〜80% braking for about 10 minutes. Pit in again and take an interval of about 10 minutes. After that, gradually increase from 80% to 100% braking and the running in of rotors on circuit is completed.
Advantages and disadvantages of having slots

Generally more slots the higher operating friction level, but increases air noise (noise from the discs rotating) and faster pad wear.


What is the heat resistance temperature of brake discs?

Unlike brake pads, it is not precise to indicate disc heat resistance temperatures in the form of 'up to ℃'. All brake discs are made of generally the same material, so they all run the risk of possible thermal cracking and distortion when temperatures reach 600℃ or higher.

Many different factors cause these problems, so we do not specify the heat resistance temperatures of brake discs.

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