Girodisc Front 2-Piece Floating Rotor Set - E46 M3, E85/E86 Z4M

These Girodisc 2-piece rotors are a direct replacement for the E46 M3 345mm rotor found on Competition Package (ZCP) and CSL models. Weighing in at 17.5 lbs per rotor versus 19 lbs per factory rotor, these fully floating assemblies help shed unsprung weight and rotating mass from the front axle of the vehicle.

The rotor rings are machined from a proprietary casting made of high-carbon steel formulated to Girodisc’s specifications. This superior metallurgy results in a rotor that holds up better, and the 48 curved vanes act as a centrifugal pump pulling air in through the hub to effectively cool the rotors under hard use. The 2-piece design means a reusable hat which can be attached to new rings (part number D1-012) when they need to be replaced.

All major components including the hats, rotor rings, and drive pins are manufactured in-house at Girodisc's facility in Bellingham, WA from domestically sourced materials. The hat is made from 6061-T6 aluminum and coated in a black anodize finish. The drive pins are made from a high-strength steel alloy and cadmium-plated for corrosion resistance. All rotors are assembled with spring clips and Belleville washers for race-ready float while also being street-friendly with no noise from loose hardware.

Our E46 M3 rotors have been designed with common aftermarket caliper setups in mind, in addition to the stock sliding calipers available on ZCP and CSL cars. These setups include the Brembo calipers from both the Porsche 996 and Megane RS swaps.

Diameter: 345mm
Thickness: 28mm
Weight: 17.5 lbs per rotor assembly

The minimum thickness at which we recommend replacing these rings is 26mm. We also recommend replacing them if a crack leads to the edge of the ring.

Sold/priced per pair.

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This application is only for E46 M3 Coupe and Convertible, E85 Z4M Roadster and E86 Z4M Coupe models fitted with the ZCP or CSL braking system.

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The primary purpose of the Girodisc system is to reduce unsprung and overall vehicle weight. The secondary purpose is to increase the ventilation and cooling capacity of the brake disc while retaining it's original dimensions. This is accomplished by using two-piece disc construction. The central “hat” section of the disc is made from 6061-T6 aircraft specification aluminum.

The disc is made from cast iron, to the same specification and material as used by professional racing organizations. It is a curved vane design, developed in racing to act as a centrifugal pump to force cooling air through the disc. The rotor and hat have a floating mount system, which utilizes  high strength alloy steel drive pins, manufactured by Girodisc to our own specifications and cadmium plated for a long lasting corrosion resistance. These pins take the load from braking actions while maintaining the axial and radial float between the hat and disc. The pins are secured by grade 12 cap screws with hardened washers. In order to keep the rotors from making noise when cold, the pins are mounted with anti-noise spring clips on the rotor side which allow the rotor to grow with heat expansion but eliminate the rattle and noise associated with floating rotors. This float also allows the rotor to self center between the pads.

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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.

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.

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.

Girodisc does not recommend drilled discsfor 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 (see photos).

Should new discs and pads be bedded in and if so, how?

Which direction should the discs rotate?