Brake pads, fluid and bedding-in - the deep guide

Brakes are safety-critical. This is a deeper companion to "Brakes: pads, lever feel and braking setup" (slug: brakes-and-braking-setup) - that article covers lever feel and the setup-serves-technique idea; this one goes into pad compounds, the bedding-in procedure with cited numbers, brake-fluid chemistry and boiling points, telling fluid fade from pad fade, and disc/pad wear limits. Every number below traces to a named source in the sources list. Where a figure is model-specific or could not be pinned to one authority, it is given as a principle, not a fabricated value.

Pad compounds

Compound sets bite, feel, heat capacity and disc wear - pick for the job, not by price.

• Sintered / metallic - metal particles fused under heat and pressure. Strong, consistent bite, holds up when hot and in wet/dirt, and lasts longer than organic in aggressive use; can be grabby cold and is harder on discs. Sintered pads keep a consistent friction coefficient up to about ~425 °C, resist wear, and keep bite in the wet (Hardheaded Ram / Dennis Kirk). Best for track, hard road riding, and off-road mud/sand.
• Organic / resin - fibres (aramid/Kevlar, carbon, glass) in a resin binder. Softer, more progressive initial feel, quieter, gentler on discs, but less heat capacity so they fade sooner under sustained hard use (Dennis Kirk / Motorcycle.com). Best for road and lighter use where feel and low noise matter.
• Ceramic - a subset of sintered using ceramic instead of metal content. Handles high race heat loads but takes longer to reach temperature, so it is less ideal cold on the street; some riders feel it has less bite than sintered (Motorcycle.com). Best for track/race where the pad stays hot.
• Carbon - road "carbon" pads are actually hybrids (sintered-carbon or carbon-ceramic); true full-carbon brakes are MotoGP/F1 only and need to be very hot to work (BikesRepublic). EBC's Carbon TT/X off-road pads are a carbon-copper hybrid aimed at cooler disc temps and reduced rotor wear (EBC).

Sintered pads take roughly 3-5 times longer than organic to bed in geometrically to a worn disc (EBC).

Bedding in new pads (and discs)

Bedding-in transfers an even layer of pad material onto the disc and heat-cures the pad ("green fade" - the resins cure and burn off). Skip it and you get a wooden lever, uneven bite and glazing (Galfer / EBC). The principle for every brand: a series of progressively harder stops from speed, WITHOUT coming to a full stop and without dragging the brake, letting them cool between runs. Do not stop with hot discs - the transfer keeps depositing in that one spot and creates a thick patch (EBC).

Cited procedures (they differ by brand and pad type - follow the maker of your pad)

• Galfer (motorcycle): start with slow stops of about 15-25 km/h, increasing in blocks of ~15 km/h up to about 65-80 km/h; repeat the sequence 2-3 times, then ride normally. Bed onto clean rotors (Galfer).
• EBC organic (street): drive gently for the first ~500-650 km, braking lightly and intermittently; expect an odour/smoke as surface volatiles burn off during the final high-end bed-in (EBC).
• EBC sintered SR race series: no chemical bedding - just mate to the disc, about 3-5 snubs from ~145 to 30 km/h with full acceleration between snubs if the disc is flat/new (EBC).
• Brembo: bedding lasts about 300 km, using brief and gradual braking to align the pad to the disc; avoid sharp/violent braking which overheats the friction material (Brembo). Brembo's car-side procedure gives the underlying pattern - at least ~30 light-to-medium applications of ~3 seconds from varying speeds, at least ~800 m apart, to raise temperature without thermal shock (Race Technologies, Brembo partner).

When you fit new discs, add bed-in time: even a flat disc has to "square up" to reach ~90% contact - watch the contact patch widen across the disc before you ride hard (EBC).

Brake fluid and fade

Two chemistries. Do not mix across them.

• DOT 3 / DOT 4 / DOT 5.1 are all glycol-based, hygroscopic (they absorb water) and mixable with each other (Brake fluid, Wikipedia; getradingeg).
• DOT 5 is silicone-based, hydrophobic, NOT mixable with glycol fluids and not suitable for ABS (silicone holds air bubbles that ABS pulsing injects, giving a spongy feel); mixing causes sludge and seal damage (getradingeg / freeasestudyguides / Wikipedia).

Dry vs wet boiling point. Dry means fresh fluid from a sealed container; wet means the fluid has absorbed 3.7% water by volume, per the FMVSS/SAE test (Epic Bleed Solutions). FMVSS 116 minimums

• DOT 4: dry >= 230 °C, wet >= 155 °C (r1concepts / Epic Bleed Solutions).
• DOT 5.1: dry >= 260 °C, wet >= 180 °C (Motorex; FMVSS 116). These are the spec MINIMUMS; a specific branded fluid can be higher (e.g. EBC BF-307 quotes a 307 °C dry point) (EBC). Use the number on your bottle, not the minimum.

Why fluid fades over time. Glycol fluid absorbs roughly 1% or more water per year; a two-year-old system can hold 2-3% water, and about 2% water drops a DOT 4 fluid's boiling point by roughly 45 °C (LinkedIn/Mucevski; MISCO). Lower boiling point -> under hard braking the fluid boils, forms compressible vapour, and the lever goes soft. That is why fluid is changed on time, not mileage: EBC advises changing fluid about every two years for street use (and every 2-3 events, or every event, for track/race); many vehicle makers specify every 12 or 24 months (EBC; LinkedIn/Mucevski). Follow your bike manufacturer's interval.

Fluid fade vs pad fade - how to tell them apart:

• Fluid fade (boiled fluid): the lever goes soft/spongy or pulls to the bar with little stopping power - air/vapour is compressing (Demon Tweeks).
• Pad fade (glazing/overheat): the lever still feels firm, but stopping power drops however hard you squeeze - the pad binder has overheated and smeared (Demon Tweeks). Firm lever + weak braking points to the pad; soft lever points to the fluid.

Bleeding (brief)

Air in the lines compresses, so a system with air feels spongy - the fix for a spongy-from-air or old-fluid lever is a proper bleed with fresh fluid until the lever is firm. This is a careful job (correct fluid, no air ingress, no contamination, keep the reservoir topped); if you are unsure, have a workshop do it. Fitting thicker new pads raises fluid level, so check the reservoir is not overfull, which can drag the brake (Galfer). Principle-level only here - see a service manual for the exact procedure.

Lever feel

Set lever span so your fingers reach it with a slight bend and pull to the bite point without trapping the other fingers, with a little free play before the bite; too far out makes you stretch, too close and you run out of travel under hard braking. Match the rear pedal height so you can cover it without lifting your foot. One- or two-finger braking frees the rest of your hand for grip and control. This mirrors the lever guidance in brakes-and-braking-setup - see that article for the setup-serves-technique framing.

Discs and wear

• Minimum disc thickness is stamped on the disc (or given in the manual); replace the disc at or below that MINimum THickness, or when you find deep circular scoring, radial cracks, blue/dark heat spots, or measurable deformation (Brembo). The exact number is model-specific - as a cited example of the concept, one bike quoted a ~5.0 mm new front disc with a ~4.5 mm service limit, others stamp a lower figure right on the rotor (community/forum reports). Always read the number on YOUR disc; do not assume one value.
• Warping / uneven thickness shows up as pulsing or judder through the lever.
• Pad wear: replace before the friction material runs out. The UK legal limit is 1.5 mm; a common conservative rule is to start planning a change around 2 mm and replace before 1.5 mm, and to check the service limit in your manual (Trodo; MTX Braking). Also replace pads that are glazed, contaminated (oil/fluid), or unevenly worn.

Off-road notes (MX / enduro)

• Mud and sand are brutal on pads - some pros get only ~30 minutes from a set; heavy-duty sintered (e.g. EBC R series) is the usual choice for mud (Motocross Action / EBC).
• The slotted pattern on off-road discs helps fling mud off the disc; keep pads and disc clean of mud/grit so they can bite (Motocross Action / Brembo).
• Oversize discs give a noticeable increase in braking power over the OEM disc, usually needing an adapter to reposition the stock caliper (24MX / Motosport).

Safety

Startpunkt, keine Sicherheitsgarantie - Bremsen sind sicherheitskritisch, im Zweifel Fachwerkstatt. Starting point, not a safety guarantee - brakes are safety-critical; if in doubt, use a qualified workshop.