Girodisc A1-307 front brake discs, measuring 348 × 36 mm, enhance braking endurance during sustained use on the BMW M240i (G42), M340i, M440i (G2X) (2019+), BMW X3, X4 M40i (G01, G02) (2018+), BMW Z4 M40i (G29) (2019+), and Toyota Supra GR (2019–2026). Their cast-iron pads and aluminum hubs form a floating assembly designed to manage thermal stress and facilitate pad replacement due to wear. Sold as a pair, including one left and one right disc bell.
These rotors are intended for the front axle of compatible vehicles in the configuration shown below. They retain the compatible caliper mounting; any required spacers and brake pad specifications must be observed.
The curved internal cooling fins channel air through the rotor to dissipate heat during repeated braking. The floating mounting minimizes stresses caused by thermal expansion differences between the rotor and the housing and helps the rotor center itself between the brake pads, maintaining consistent contact under heat.
The hub is made of 6061-T6 aluminum. The high-strength steel drive pins are cadmium-plated to resist corrosion. Spring washers minimize cold-mounting noise while allowing the necessary compression for the floating mount.
New brake pads must be installed with new discs or rotors. Their shape and compound must be compatible with the mounting, casting, and intended use; adhere to the specific requirements for this part number and perform the prescribed break-in procedure.
Each application is subject to its specific brake system, calipers, and any requirements for brake pads or spacers. Please verify these requirements before ordering.
Choose brake pads whose shape is compatible with the calipers, track, and/or A1-307 rotors, and whose compound is suitable for sport driving or track use. The Endless, pagid Racing, or Ferodo Racing ranges may be considered after verifying the appropriate part number.
For intensive use, we recommend compatible aviation-grade flexible hoses and high-performance brake fluid that meets the vehicle’s specifications, along with proper bleeding and fluid replacement. This recommendation complements the mounting, which is compatible with the original hydraulic system.
Replacing only the pads helps keep the controlled rotors in good condition. Reusing a rotor for up to three pad replacements is subject to inspection of its condition, its mounting elements, and the mounting instructions; this number does not constitute a guaranteed service life. Use a new mounting element each time the pads are replaced.
What are the sizes of the A1-307 discs for my vehicle? The part number shown measures 348 × 36 mm and is mounted on the front axle. The diameter alone is not sufficient: also check the brake system type and mounting requirements.
Is the product sold in pairs? Yes. It includes a left and a right disc for the same axle. Both discs come with their disc bells.
Do I need to replace the brake pads on my vehicle?Yes. Always install new brake pads with new rotors or new braking surfaces. Their shape and compound must be compatible with the A1-307 track and/or rotor and with the calipers. Then break in the rotors and pads according to the prescribed procedures.
How do I identify the left and right sides? Girodisc rotors come with a label attached to each rotor: LEFT for the left side and RIGHT for the right side, as viewed in the direction of travel. On a left-hand-drive vehicle, “LEFT” corresponds to the driver’s side and “RIGHT” to the passenger side. Follow these labels and the instructions. On models with curved internal fins, the rolling direction depends on this internal ventilation; the surface grooves alone are not sufficient to determine the side.
How do I break in this mounting on my vehicle? Follow the Girodisc procedure and the brake pad manufacturer’s instructions to build up an even transfer ply. The PDF documents below detail installation and break-in.
We have included two PDF documents below: an instruction manual for installing and breaking in the discs, and an instruction manual for installing new tracks on existing bowls. Consult the document that applies to your specific task before you begin.
