Tyre construction, compounds, break-in and reading wear (web-validated)

This guide covers what a tyre is made of, what the compound codes mean, how to scrub a new tyre in, why race tyres "wear out" by heat cycle, and how to read the story a used tyre tells. Pressure and choice-by-condition are covered separately - see tyre-pressure-by-condition, tire-choice-by-condition, enduro-tyre-mousse-guide and track-tyre-warmers-and-temperature. Every substantive number below is traced to a named source; where a figure could not be validated, only the direction is given and it is flagged as a principle.

Construction: bias-ply vs radial

• Bias-ply (cross-ply): the fabric plies run diagonally bead-to-bead, typically at 30-45 degrees, with successive layers crossing. Bias tyres do not shed heat as well and are not the first choice for sustained high speed, but they carry load well and clear/conform on varied terrain, which is why they persist off-road and on smaller/older/heavier bikes (RevZilla, Dunlop, Witchdoctors).
• Radial: cords run straight across (about 90 degrees) from bead to bead, paired with stabiliser belts. Radials dissipate heat better (so they suit high speed and track), give a larger, more even contact patch, and have more flexible sidewalls that provide more feedback (Dunlop, Michelin, RevZilla, Witchdoctors).
• Chassis caveat: a radial's construction is fundamentally different, so fitting radials to an old bike not designed for them can overload the frame/swingarm and handle poorly - ask the tyre maker before swapping construction types (Michelin technical manager, via Bennetts BikeSocial).

Dual-compound. Many road/sport tyres use two compounds across the tread - a harder centre for durability under the kilometres spent upright, and softer shoulders for cornering grip (2CT = "Two Compound Technology"). Michelin's first road dual-compound tyre was the Pilot Power 2CT (dual-compound tech dating to the 2005 Power Race) (Two Tyres, Michelin history via Rider/Motorcycle.com).

Compounds: soft, medium, hard - and what each is for

A softer compound grips harder and warms up faster but wears faster; a harder compound is more durable and works over a wider temperature range but gives less outright peak grip. Crucially, a compound is designed for a temperature window, not simply "grip vs no grip".

Pirelli Diablo Supercorsa SC (verbatim from Pirelli): compounds run in sequence from soft to hard - SC0 (softest), SC1, SC2, SC3 (hardest). Pirelli's own guidance

• SC0 - softest, for high temperatures and smooth (low-grip) tarmac; a soft compound can penetrate a hot, slick surface better.
• SC1 - also soft, more pliable, wider temperature/tarmac margin than SC0.
• SC2 - intermediate, suited to lower temperatures and more aggressive tarmac (rough cold tarmac gives more mechanical grip but can tear a soft tyre, so more mechanical strength is needed).
• SC3 - hard, wide temperature range including cooler conditions; Pirelli explicitly recommends SC3 front and rear for typical track-day use because it works over a wide range, suits smooth or aggressive tarmac and lasts longer. Pirelli warns not to trust the words "hard" and "soft" alone: consistency varies with temperature, and running a soft SC0 too cold does not give maximum performance and can damage/tear the tyre (Pirelli).

Michelin, Dunlop, Bridgestone and Metzeler use their own soft/medium/hard designations on their race ranges; treat the maker's own chart for your exact tyre as the authority rather than cross-mapping brands by feel.

Off-road terrain compounds (see tire-choice-by-condition for the full pattern-by-terrain table): MX tyres split by terrain - soft/sand, soft-to-intermediate, and hard/hardpack knobblies. Dunlop's Geomax range spans this (e.g. MX33 soft-to-intermediate, MX34 intermediate-to-hard), Michelin's Starcross family and Pirelli's Scorpion MX likewise. On loose ground the open pattern (scoop) matters more than the rubber; on hard ground a tougher carcass and closer knobs resist tearing.

Breaking in a new tyre (scrub-in)

A new tyre has a smooth, slightly slippery surface and handles differently from the worn one it replaced, so it must be worn in progressively before hard use. Makers still warn about this even where mould-release agents are no longer used, because - in Michelin's technical manager's words - "the vulcanisation and cooling process of every tyre still causes oils and waxes within the rubber compounds to raise to the surface and form a sheen. This can be very slippery and take a number of kilometres to wear off, even where non-stick tyre moulds have been used without a mould release agent" (Bennetts BikeSocial, quoting Michelin).

Maker-stated run-in distances (verbatim, road):

• Michelin: at least 100 km.
• Bridgestone: ride slowly/carefully for the first 100 km.
• Pirelli / Metzeler: ride very cautiously for the first 100-200 km.
• Avon: minimum 160 dry km before maximum power, then re-check pressure.
• Dunlop: approximately 160 km before maximum power, abrupt lean or hard cornering; re-check/adjust pressure after the tyre cools at least 3 hours. (All the above from Bennetts BikeSocial, which sourced them directly from the makers.)

Technique: avoid hard acceleration, hard braking and high lean until scrubbed in, and progressively use the unworn tread by leaning a little more each corner - a small amount first, then more, overlapping worked areas, and doing both left and right sides. Do not ride 80 km of motorway upright and then try to get a knee down at the first roundabout (Bennetts, Michelin, Dunlop). On track a good rider scrubs a new pair in over a few progressive laps rather than road kilometres.

Heat cycles (track / DOT-race tyres)

A heat cycle is one complete warm-up from ambient to the tyre's working temperature followed by a complete cool-down back to ambient (Tire Rack, Grassroots Motorsports). Track and DOT-competition rubber is heat-cycle limited: repeated heating/cooling gradually hardens the compound and reduces grip, so a race tyre can lose pace from heat aging before it physically wears out.

• The first heat cycle matters most. Running a brand-new DOT-competition tyre too aggressively, too hot or too long on its first outing breaks some of the stronger internal bonds and permanently reduces grip and wear (Tire Rack). The recommended practice is to bring it up to temperature gently on the first cycle, then let it rest.
• Rest after the first cycle. Sources advise letting a freshly heat-cycled tyre relax (commonly stated as around 24 hours) so the rubber's molecular bonds re-link, which is said to improve consistency and life (Tire Rack, Grassroots Motorsports).
• How many cycles? This is tyre-specific and stated as a range by track sources, not a single manufacturer figure: DOT R-compound tyres are commonly quoted as heat-cycle limited to on the order of a dozen or so true cycles (various track sources cite figures around 6-12, others 15-20). Treat the exact number as directional - the tyre still functions past its heat-cycle "life", it just no longer sets a best lap. (Tire Rack, UsedRacingTires, Grassroots Motorsports.) A specific per-model cycle count from a tyre maker was not validated here, so no fixed number is asserted.

Warmers relate directly to this - see track-tyre-warmers-and-temperature for warm-up time and setting hot-target pressure on the warmer.

Reading wear - the tyre tells you what happened

Road / track

• Graining: a rippled, many-tiny-tears look where surface rubber shears and re-fuses. Typically the surface is being worked while too cold/too hard for the load - e.g. pushing a cold tyre hard, or a compound too hard for the day (Life at Lean, Suspension Secrets).
• Cold tear: deeper tears; the surface heats but the carcass stays cooler and resists, so the surface rubber tears. Associated with the tyre running too cold and/or over-inflation (contact patch too small to generate heat across the carcass) (Bennetts, Suspension Secrets, Life at Lean).
• Hot tear: shallower, more spread-out tearing / a molten, shiny smear at the edge; the tyre is overheating - classically under-inflated for the pace (or too soft a compound), so the contact patch is too large and works too hot (Bennetts, Suspension Secrets, Life at Lean).
• Blueing / greasy sheen: motorcycle tyres contain oils that keep the rubber soft; after heavy heat and cool-down (a heat cycle) those oils rise to the surface as a blue/green tint or greasy film. The more heat cycles, the more oil is lost and the less the rubber works - a sign the tyre is heat-aged and greasing off (Life at Lean).
• Centre vs shoulder wear (pressure/geometry): Michelin states over-inflation wears the centre faster and under-inflation wears the shoulders faster; uneven or one-sided wear also points to pressure, alignment or suspension. Both shoulder and centre wear count toward the legal limit - if the limit is reached at any one point, replace the tyre (Michelin wear-and-tear and tread-depth pages). "Cupping/scalloping" (scalloped dips) is commonly linked to suspension damping/pressure issues rather than compound; this is stated here as a directional principle, as an exact single-cause manufacturer statement was not validated.

Motocross / off-road

• Knob tearing / chunking / rounding: knobs tearing at the base, chunks breaking off, or knobs rounding over are read as a compound-to-terrain mismatch (often too soft a compound and/or too-low pressure for hard ground), and an aged tyre is more prone to ripping and chunking as the rubber hardens with age (Vital MX, Dunlop care page). Rounded, torn or missing knobs mean the tyre has lost its bite and edge - replace it. Match the terrain first (see tire-choice-by-condition).

The wear indicator and legal depth

Tyres carry moulded Tread Wear Indicators (TWI): small raised bars in the main grooves. Michelin states these appear (grooves become smooth/level) at about 0.8 mm remaining tread; Michelin marks their location with the "Michelin Man" symbol, other brands print "TWI" on the sidewall (Michelin). Legal minimum tread depth is jurisdiction-specific and NOT a single number: the EU passenger-car limit is 1.6 mm, but motorcycle-specific limits differ by country - e.g. the UK requires 1 mm across three-quarters of the tread width (with visible tread on the remainder) for motorcycles over 50cc, and France sets 1 mm; mopeds up to 50cc must simply show the full original pattern (Michelin, Two Tyres, cashforcars). Check your own country's rule. Verify: EU car figure (1.6 mm) is validated; the "1.0 mm motorcycle over 50cc" figure is validated for the UK specifically, not as a blanket EU number.

Age and when to replace

• DOT date code: the last four digits after the DOT code on the sidewall are the build date - the first two are the week, the last two the year (e.g. 1420 = 14th week of 2020). Only one sidewall carries the full code (utires, Front Wheel Up, MotoFomo).
• Rubber ages even unused. It oxidises and dries out with exposure to air, heat and UV, hardening and losing flexibility and wet grip; storage conditions, repeated heat cycles and running low pressure all speed this up (utires, Dunlop).
• Inspect from about 5 years, replace by about 10 years. Common maker/industry guidance is to have tyres inspected once they reach roughly 5 years old and to replace them by about 10 years from the date code even if tread remains - sooner if you see cracking, hardening or poor grip. Bennetts notes motorcycle tyres are generally guaranteed for around 5 years from manufacture, dependent on storage (Dunlop, Front Wheel Up, Bennetts). The exact "5 / 10 year" wording varies by maker, so treat it as the widely-stated principle and defer to your tyre maker's own statement.

Starting point, not a safety guarantee - always inspect yourself and follow the manufacturer's specifications.