Girodisc Replacement Rotors

Girodisc replacement rotors deliver many layers of performance braking improvement offering great value to aggressive street and track Porsche owners.  Depending if you have an older Porsche or later base or a GT model, Girodisc replacement rotors can improve cooling, reduce weight, improve durability, reduce replacement cost or improve braking feel.

2 piece Rotors

Many non GT Porsches, especially older models have solid brake discs.  2-piece rotors are a great braking improvement for any aggressive street or track day owners.  2-piece rotors have several main features and value like floating outer rings, lightweight aluminum and cooler running hats and potentially lower replacement costs.

Floating outer ring allows a hotter outer ring to expand and naturally shift independent vs the hat which can be hundreds of degrees cooler than the ring when on track or even aggressive canyon carving.  By allowing the running to expand and shift independently from the hat, there is less stress between the two significantly reducing the potential to crack.

2-piece rotors allow for the hats to be made in a much lighter weight aluminum potentially reducing several lbs/kgs off the rotor weight.  The hats don’t experience anywhere near the temperature of the rings and thus don’t need to have the high heat strength of iron.  Even though rotor hats are technically rotational weight, you will not get the 4-5X static weight multiplier benefits as wheel weight savings as the weight is closer to the rotational center and doesn’t require as much force to accelerate or decelerate.  However, taking a few lbs/kgs off the hats provide an unsprung weight benefit allowing the wheels undulate faster improving the suspension dynamics and tire contact during dynamic movements.

Additionally, 2-pierce rotors also reduce heat transfer from the rings to hat and thus heat transferred into the wheel hubs.  Heat transfer between 2 different materials is lower than a single solid material.  Overheating wheel hubs will increase wear that can lead to premature failure or replacement.

Finally, 2-piece rotors can reduce replacement costs for some models as dealer rotor replacement costs can be high.   Thus, replacing only the rings vs the entire rotor can reduce total cost of ownership for some models.

Curved Vanes

Another feature that Girodisc replacement rotors have that some Porsche OEM rotors may not are curved vanes.  Curved vanes provide 2 main cooling benefits.  First, curved vanes act like an impeller accelerating air faster through the rotor versus straight vanes improving cooling.  Additionally, curved vanes are longer than straight vanes and generally provide more overall surface area increasing heat transfer from the hotter disc to the cooler air accelerating through the rotor.

Slotted Rotors

An often-overlooked benefit is slotted rotors vs drilled rotors.  We have to admit, drilled rotors look great and in some situations even shed weight.  However, the biggest issue with drilled rotors is they provide stress risers for cracks to initiate.  It doesn’t take much effort to search for “Porsche cracked brake rotors” and you will find countless concerns from owners.  Further proof of fragility of drilled rotors is that you will not find any advanced racing cars running them.

Additionally, slotted rotors provide another benefit of keeping the brake pad clean and deglazed.  Dirt and debris can land on the rotor contaminating the pad.  Additionally, during extreme braking events, the pad can temporally exceed its material temperature range causing it to glaze changing its surface friction.  Glazing can escalate creating a thick tough layer of reduced friction pad material that feels wooden.  Slotted rotors continuously keep the top layer fresh preventing it from glazing over.  Almost all top-level racing uses some form of slotted rotors to provide a consistent pad feel.

Potential Larger Diameter

For some non GT Porsches, Girdodisc rotors provide 10-20mm larger diameter further improving cooling while still reducing overall weight.  Slightly larger diameter rotors further increase the impeller effect and the surface area for heat transfer mentioned previously.  For several models, the extra rotor diameter is an additional bonus.

Girodisc Upgraded Diameter Replacement rotor for 981 Boxster/Cayman

Carbon Replacement

Carbon rotors are widely accepted to be lighter weight and handle higher temperatures than iron, so why would anyone want to replace carbon rotors with iron?  Carbon rotors are thousands of dollars to replace and that is an extreme maintenance cost for a relatively high wear item.  We can offer a set of Magnesium wheels with much more weight reduction for a similar replacement cost of carbon rotors.

Additionally, Carbon rotors don’t provide the control of iron rotors as they don’t modulate well.  Carbon rotors can feel on or off depending on the temperature, meaning you either get full braking or no braking.  There are many great pad options for iron disc providing controllable braking from full to moderate to light forces that are needed in varying situations.  You don’t always want the hardest braking possible and carbon rotors simply doesn’t provide the modulation that iron disc do.

Important Questions Answered

Q: What is required to install the Girodisc system?

A: The Girodisc system is a direct replacement for the OE disc.
No modifications are necessary. The disc will bolt directly to the car and work with OE calipers and pads perfectly. Once the Girodisc system is in place, simply replace the cast iron rotor when needed. Some discs are larger in diameter and come with caliper spacers. If longer bolts are required, they are also supplied.

Q: How does reducing weight of the braking system benefit the vehicle?
A: The Girodisc will generally weigh between 4 – 8 lbs less than the oe disc it will replace. This is due to the heavy cast iron hat section being replaced with lightweight, high strength aluminum. The mass of any vehicle requires energy to accelerate or decelerate. Reducing the vehicle mass improves acceleration, and requires less energy to be dissipated during deceleration. Rotating mass requires additional energy in order to increase or decrease its speed of rotation. Decreasing the mass of the disc has a great benefit due to reduction in rotational inertia. This will allow more of the braking force to be available to decelerate the vehicle, not the disc.
Additionally, the mass of the brake system is also unsprung mass. Reducing the unsprung mass has the additional benefit of improved suspension performance, resulting in enhanced ride and handling. Rotating masses require additional energy to vary the plane on which they turn. The lighter the disc, the quicker the response of the vehicle steering due to the reduction in gyroscopic effect/rotational inertia of the disc. As an example, compare the weight of the Ferrari 360 OE disc at 18.2 lbs, and the Girodisc at 14 lbs. The Girodisc is 4.2 lbs lighter per disc. Replacing all four discs will save 16.8 lbs of rotating, unsprung mass.

Q: Why slotted discs?
A: The edges of the slots continuously clean and refresh the pad surface. This will allow the pads to have a maximized friction surface always available. Additionally, they prevent containments from collecting between the pad and disc interface.
The disc is lightened, decreasing its rotational inertia.
Slots prevent the formation of a water film on the disc in wet weather, maintaining the best brake response.

A note on drilled discs:
Girodisc does not recommend drilled discs for high performance applications. The rapid heating and cooling cycles will cause cracking on the friction surface of a drilled disc. The use of high friction or racing pads will exaggerate this condition. Most pad manufacturers specifically recommend that their race pads not be used on a drilled disc for this reason. Girodisc can drill discs for an additional fee,  if the customer is aware of the potential hazards of drilling the discs.
Note as example the cracking in this OE Ferrari 550 drilled disc after one track day. Also note this custom front disc of a Porsche 993 Turbo after hard use.

OE Ferrari 550 drilled disc showing cracks after one track event	Drilled disc showing cracks after one weekend of hard track use

Q: Should new discs and pads be bedded in and if so, how?
A: The answer is yes, for optimum performance, any time different friction materials or discs are introduced, a bedding procedure should be carried out.

Q: Which direction should the discs rotate?
A: For maximum airflow and superior cooling, the Girodisc system uses curved vanes. For a curved vane internally vented disc, the geometry of the vanes dictates the direction of rotation. A curved vane disc must be installed with the vanes running back from the inside to outside diameters in the direction of rotation. Your discs will come with labels indicating their correct placement on the vehicle. Orienting the disc in this manner creates a centrifugal pump. The rotation of the disc causes air to be pumped from the center of the disc, through the vanes, and out through the outside diameter of the disc. This greatly enhances the disc’s ability to dissipate heat. Discs installed backwards have very limited cooling.