Bike Brake Rotor Standards: Sizes, 6-Bolt vs Centerlock, Thickness & Compatibility

Also called: ISO 6-bolt, International Standard 6-bolt, IS 6-bolt

6 bolts on a 44 mm bolt circle; M5 x 0.8 thread; Torx T25 (or 3 mm hex) heads; 4-6 Nm torque

The original and still most universal way to attach a rotor to a hub: six small bolts pass through the rotor into threaded holes arranged in a 44 mm circle on the hub shell. Any 6-bolt rotor fits any 6-bolt hub regardless of brand. Bolts are tightened in a star (alternating) pattern with threadlocker and no grease.

Why it exists: Adopted industry-wide in the late 1990s as disc brakes arrived on mountain bikes, giving every hub and rotor maker a single shared bolt pattern.

Typically found on: Most mountain bikes, e-MTBs, budget and mid-range bikes of all types, and almost all aftermarket hubs

Also called: Center Lock, CL, splined rotor mount

Splined interface on the hub; lockring torqued to about 40 Nm; internal-spline lockrings use a cassette lockring tool, external-notch lockrings use a 16-notch bottom-bracket tool

Shimano's alternative to 6-bolt: the rotor has a splined center hole that slides onto matching splines on the hub, secured by a single threaded lockring. Installation is faster and self-centering, but you need the right lockring tool. Lockrings come in two styles: internal-spline (the common type, fitted with a cassette tool) and external-notch (fitted with a bottom-bracket tool, required when a 15 or 20 mm thru-axle would block the cassette tool).

Why it exists: Shimano introduced it around 2003 to make rotor swaps quicker and more consistent than torquing six tiny bolts. Originally patented, it is now licensed and offered by most hub and rotor brands alongside 6-bolt.

Typically found on: Shimano-equipped bikes, most modern road and gravel disc bikes, and many higher-end MTB wheelsets

Also called: 140/160/180/200/203/220 mm

140, 160, 180, 200 or 203, 220 or 223 mm outer diameter, in roughly 20 mm steps

Rotor sizes step up in about 20 mm increments, and each step needs a matching caliper position (native mount or adapter). Road and cyclocross bikes use 140-160 mm; gravel and commuters typically 160 mm; cross-country MTB 160-180 mm; trail and enduro 180-200/203 mm; downhill and heavy e-MTBs 200-223 mm. Bigger rotors give more leverage and heat capacity at the cost of a little weight.

Why it exists: Different disciplines need very different amounts of braking power and heat management: a 60 kg road racer on short brake taps needs far less rotor than a 25 kg e-MTB descending alpine trails. Standardized steps let one caliper serve every size via adapters.

Typically found on: 140/160 mm on road and gravel; 160-180 mm on XC and commuters; 180-203 mm on trail/enduro; 200-223 mm on downhill and e-MTB

Also called: SRAM 200, Shimano 203

3 mm of diameter, i.e. 1.5 mm of caliper radial position

The 'eight-inch' rotor exists in two nearly identical sizes: Shimano, Hope, TRP, Galfer and most others make 203 mm rotors, while SRAM standardized on 200 mm (and 220 mm rather than 223 mm). They are close enough to look identical but far enough apart that a caliper set for one will sit wrong on the other, causing rubbing or reduced pad contact.

Why it exists: Early brands rounded 8 inches (203.2 mm) differently; SRAM later chose even 200/220 mm sizing. Both persist, so adapters and washer kits are sold specifically to convert between them (a 1.5 mm spacer under the caliper adapts 200 mm hardware to a 203 mm rotor).

Typically found on: 203 mm on Shimano/TRP/Hope-equipped bikes; 200 mm on SRAM-equipped trail, enduro, DH and e-bikes

Also called: 1.8 mm rotors

Shimano: 1.8 mm new, replace at 1.5 mm; SRAM Centerline: 1.85 mm new (some 140 mm are 1.9 mm), replace at 1.55 mm; Hayes: replace at 1.52 mm

For most of the disc-brake era, rotors have been about 1.8 mm thick when new. The braking surface slowly wears thinner; every rotor carries a stamped minimum thickness (e.g. 'Min.TH=1.5') below which it must be replaced. Wear limits vary slightly by brand, so check your rotor's own marking.

Why it exists: 1.8 mm balances weight, stiffness and pad clearance inside the caliper. Wear limits exist because a too-thin rotor overheats, warps and can fail, and because pads can over-extend past their pistons' safe travel.

Typically found on: Nearly all road, gravel, commuter and mountain bikes before ~2021, and most non-e-bike rotors today

Also called: SRAM HS2, Galfer E-bike Wave, heavy-duty rotors

2.0 mm thick (SRAM HS2, Galfer e-bike, Magura MDR-P class); some DH/e-cargo rotors 2.3 mm; sizes 160-223 mm plus oversize 246 mm options

A newer generation of thicker rotors built for e-bikes, enduro and downhill. SRAM's HS2 (160/180/200/220 mm, 6-bolt and Centerlock) is 2.0 mm thick versus 1.85 mm for its Centerline line, claiming more power and better heat handling. Galfer's MTB/e-bike Wave rotors are likewise 2.0 mm. The extra metal resists warping and fade under the sustained braking loads of heavier, faster bikes.

Why it exists: E-bikes added 10-15 kg and higher average speeds, overwhelming 1.8 mm rotors on long descents. Thicker discs store and shed more heat and stay stiffer under hard braking.

Typically found on: E-MTBs, e-cargo and commuter e-bikes, enduro and downhill bikes from roughly 2021 onward

Also called: floating rotors, alloy-carrier rotors, Shimano Ice-Tech Freeza, Hope Floating

Same diameters, mounts and thicknesses as one-piece rotors; steel braking ring riveted to an aluminum center carrier

Instead of a single stamped steel disc, two-piece rotors attach a stainless braking ring to a machined aluminum spider. This saves weight, pulls heat away from the braking surface, and lets the ring expand slightly ('float') when hot without warping. Shimano's Ice-Tech rotors go further, sandwiching an aluminum core between steel faces. Functionally interchangeable with one-piece rotors of the same size, mount and thickness.

Why it exists: Borrowed from motorcycle practice to manage heat on long descents and shave weight on premium builds.

Typically found on: Higher-end mountain and road groupsets (Shimano XT/XTR/Dura-Ace, Hope, Magura MDR-P, Galfer two-piece)

By markings

Almost every rotor has its specs laser-etched on the face: diameter (e.g. '180' or 'SM-RT64 180'), minimum thickness (e.g. 'Min.TH=1.5'), a rotation arrow, and often the model name (Shimano RT-MT800, SRAM Centerline or HS2, Galfer Wave). Shimano rotors marked 'Resin Pad Only' must not be used with metallic pads. If the etching has worn off, measure instead.

By measuring

Diameter: measure straight across the rotor through the center of the axle with a ruler or tape; you should land within a millimeter of a standard size (140/160/180/200/203/220). If you read about 185 or 170 mm you have a legacy size. Thickness: use calipers on the braking track (the shiny outer band where pads rub), taking readings at several points; compare against the stamped minimum. New rotors measure 1.8-2.0 mm.

By hub attachment

Look at the rotor center. Six small Torx bolts in a circle = 6-bolt. A single large ring holding a splined rotor = Centerlock. On Centerlock, check the lockring: notches around its outside edge = external type (bottom-bracket tool); splines inside the hole = internal type (cassette lockring tool).

By caliper hardware

The adapter between caliper and frame/fork often carries its own marking (e.g. 'PM 180', 'IS-PM 203', '+20 mm'), which confirms the rotor size the bike was set up for. On road/gravel flat-mount bikes, no adapter usually means a 140 mm rear or the frame's native size; a thin adapter plate usually means 160 mm.