GREN manufactures the entire product.  We are intimately involved throughout the whole process, providing us with a unique advantage of controlling the quality of the product from casting to final machining.  We use our own designs, castings, manufacturing facility, and highly trained skilled workforce.


Our commitment to providing nothing less than the finest quality products is backed by our consistent record of having one of the lowest return rates in the industry.


Metallurgy and Casting

Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are called alloys.  The task of a GREN metallurgist is to achieve balance between material properties such as cost, weight, strength, toughness, hardness, corrosion, fatigue resistance, and performance in temperature extremes.


Casting is a manufacturing process by which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify.  The solidified part is also known as a casting which is ejected or broken out of the mold to complete the process.  GREN uses casting to provide us with more control over the finished product as well as the fact that it would be otherwise difficult and uneconomical to make brake rotors and drums by other methods.


Following the world industrial standard, SAE J431, Grade 3000 gray cast iron is used.  We combine specific amounts of Copper (Cu) and Chroium (Cr) to make up our proprietary blend during the alloying process to achieve our desired tensile strength and hardness.  This produces unique anti-heat fade characteristics specific to GREN.


We precisely control temperatures during casting to create a uniform distribution of graphite flakes.  This results in an increase in wear resistance and the ability to dissipate heat.


In contrast, premature cooling of cast iron can cause iron brittleness.   This will make the brake rotor more likely to warp or crack, especially when heated under hard braking conditions.




The overall hardness of a rotor is extremely important.  Every company looks for that perfect balance.  If a rotor is too soft it will wear rapidly, too hard and it is more likely to crack.


Producing a rotor with hardness that is uneven will result in the rotor wearing unevenly or developing hard spots that cause a pedal pulsation.   Taking into account each of these issues is important as they affect brake performance and rotor life.


Brinell Hardness Test
Dr. J. A. Brinell invented the Brinell test in Sweden in 1900.  The oldest and most accurate of the hardness test methods in common use today.  The Brinell test is frequently used to determine the hardness of forgings and castings.


In the USA, Brinell testing is typically done on iron and steel castings using a 3000Kg test force and a 10mm diameter carbide ball.


GREN’S Hardness Specifications
Based on the Brinell Hardness Test, the ideal hardness to maximize pad and rotor life is HB210-200.  GREN maintains a controlled hardness extremely close to the ideal with HB215-187.


This provides even wear between pads and rotors while delivering maximum braking ability.



Tensile Strength

Tensile Strength is the maximum stress a material will sustain with uniform elongation.  At that stress, the onset of necking will occur and will continue until the specimen fractures.  This fracture will generally occur at the point of necking.


Tensile strength is calculated by dividing the maximum load by the cross-sectional area of the specimen, yielding a value expressed as pounds per square inch (psi), kilo-pounds per square inch (ksi), or Newtons per square millimeter (N/mm2).


Tensile Strength
Tensile strength is determined by the amount of carbon used during the metallurgy process.  Our tensile strength specifications are in line with industry standards at 30,000PSI.


Achieving the correct tensile strength is a daunting task.  Too high and the rotor loses thermal conductivity and thermal shock resistance as well as reduced castability, machineability, and vibrational damping capacity.  Too low and the rotor will warp and crack more easily.


GREN’S Tensile Strength Attributes
Our metallurgist’s ensure that each batch of our proprietary blend has just the right amount of carbon to achieve our desired tensile strength.  This results in our unique ability to minimize the warping and cracking of our rotors as well as maximizes the depth of our heat dam.



Vibration and Petal Pulsation

The faces of a disc brake rotor must be flat (no more than .002 to .005 inch of runout) and parallel (within .0005 inch on most cars) otherwise it will kick the brake pads in and out when the brakes are applied, producing a pulsation or vibration that can be felt in the brake pedal as the rotor alternately grabs and slips.


Lateral Runout
The wobbly movement of a rotor running out of true is referred to as lateral runout.  Lateral runout should not exceed .002 to .005 inch, depending on the vehicle manufacturer’s specifications.  Lateral runout exceeding this range can create vibration, pulsation, or brake noise.  In addition to a pulsation, a chatter, vibration, or squeal condition may be encountered.  Excessive runout can knock the pads too far from the rotor and cause increased pedal travel. 


GREN’S Lateral Runout Specifications
< .002” on 90% of SKU’s    |    < .003” on all


Lack of parallelism is a variation of the rotor thickness.   Many of the same factors that contribute to runout affect parallelism.  A thickness variation of as little as .0005 (one half thousandth of an inch) can contribute to pedal pulsation, vibrations, and brake grabbing.  While the caliper will follow some rotor runout, the pads must track an absolute parallel surface.  This is why a thickness variation of as little as .0005 inch will cause pedal pulsation. 


GREN’S Disc Thickness Variation
< .0005”