160 mm for XC, 180 mm for Trail, 200 to 220 mm for Enduro and DH. A larger disc increases the lever arm and cooling surface, thereby improving braking power and resistance to overheating. 160 mm is sufficient for XC, where the brakes are not heavily used and weight is critical. 180 mm covers most Trail and All-Mountain use. 200 mm is recommended for intensive Enduro and DH, where long descents with heavy braking generate a lot of heat. Heavier riders (+90 kg) benefit from fitting a size larger than the standard recommendation for their discipline.
Centerlock (Shimano) is fitted using a cassette tool, whilst the 6-hole (IS2000 standard) version is secured with six Torx screws. Centerlock is simpler and quicker to fit and remove: a single tool is all that is needed. The mounting ring is available in stainless steel (standard) or titanium (lightweight). The 6-hole standard is universal: compatible with all brands of hubs. Adapters allow a 6-hole disc to be fitted to a Centerlock hub and vice versa. In practice, the choice is often dictated by the hub: if the hub is Centerlock, using Centerlock discs is recommended to simplify maintenance.
When the rotor thickness falls below 1.5 mm (or 1.8 mm on some high-end models). New discs are generally 2.0 to 2.3 mm thick. The measurement is taken using a digital micrometer or a precision calliper on the friction surface, away from the cooling slots. A disc that is too thin may warp under the effect of heat during descents and cause cyclic contact with the caliper (pulsations felt by hand). The minimum thickness is engraved on some rotors or can be found in the manufacturer’s documentation.
Using a truing fork on a cold disc, make small, gradual corrections in the opposite direction to the warping. Minor warping (less than 0.5 mm) is common and can be easily corrected. Identify the warped area by spinning the wheel near the caliper and noting the side where the disc rubs. Insert the truing fork into the openings and apply a slight twist in the opposite direction to the warping. Make small adjustments: forcing the disc too much can cause it to warp in the opposite direction. Significant warping (>1 mm) or deeply scratched discs require replacement.
Coated discs (Wave, Zinc, powder-coated) offer better corrosion resistance in wet weather but wear at a similar rate. Standard 410 or 420 stainless steel discs develop surface rust in wet weather: this surface rust is normal and disappears after the first few braking actions. Coated discs (Shimano Ice Tech, Galfer Spider, Braking Silver) are more resistant to cosmetic rust, but their friction properties remain the same in the long term. Bimetal discs (Shimano Ice Tech) with aluminium inserts in the arms reduce weight by 15 to 30 g and dissipate heat more effectively.
Yes, provided the size and mounting standard match, discs are interchangeable between brands. The caliper specification dictates the compatible disc size (160, 180, 203 mm) but not the brand. A 180 mm Galfer Centerlock disc works with a 180 mm Shimano SLX caliper. Alternative brands (Galfer, Swissstop, TRP, Braking) manufacture discs compatible with all calipers, often at a price comparable to or lower than the original discs, with similar friction levels.
Isopropyl alcohol (minimum 70%) applied with a clean cloth, without greasing afterwards. Cleaning with isopropyl alcohol dissolves oil residues and pad transfer that gradually glaze the friction surface. Never use WD-40, standard degreasers or acetone. Wash the disc with soapy water first if there is mud present. Dry thoroughly before refitting. If fading persists despite cleaning, lightly sanding the friction surface (using P400 sandpaper) can restore it.
Yes, the slots and holes improve cooling, remove mud and allow the pads to self-clean. The radial slots allow gases and particles generated during intense braking to escape, reducing fading. The openings in the arms reduce weight and improve heat dissipation. Solid discs (without slots) are heavier but potentially more stable. For enduro and DH, honeycomb or 6-arm (Spider-type) designs offer the best compromise between weight, stiffness and cooling.
A rotor generally lasts 3 to 5 years with standard trail use, less with intensive use or in wet conditions. Two criteria for replacement: the minimum thickness has been reached (see previous FAQ) and warping that cannot be corrected. Deep radial grooves on the friction surface (grooves carved out by the pads) do not require immediate replacement but accelerate the wear of the next set of pads. Inspect the discs every time you replace the pads.
Yes, using a spacer adapter that moves the caliper outwards to align with the larger disc. Upgrading from 160 to 180 mm or from 180 to 203 mm requires a specific adapter (IS or Post Mount, depending on the caliper mount). Advantage: greater braking power and less hand fatigue on descents. Check that the frame/fork accommodates the desired size and that the adapter is compatible with the caliper mounting standard. High-quality adapters (Shimano, TRP, Hope) are preferable to generic parts for safety reasons.
