Tyre technology beyond conditions: regrooving, retreading standards, dual spacing

• Source / publisher: Michelin (regrooving booklet + operating advice), ETRTO Recommendations (tyre care/maintenance standard), TMC RPs on dual matching/spacing (member-gated)
• Type: guide | standard
• Topics: regrooving legality & method (3–4 mm remaining tread, rounded blade, width/depth per pattern), steer-axle regrooved-tyre rules, tyre rotation patterns (inner/outer swap, turn-on-rim, direction of rotation), dual matching (diameter/circumference tolerances), dual spacing, retread authorisation context (ECE R108/R109)
• Vehicle scope: truck | bus
• Region: global (EU-centric conventions; universally applicable)
• Language: en
• Link: Michelin regrooving guide (UK): tvs.michelin.co.uk ; Michelin operating advice (rotation + regroove timing): professional.michelin.dk ; ETRTO Recommendations ed. 2 (09/2024) — regrooving/repair/retread sections: etrto.org
• License/access: public
• Notes: complements (does not duplicate) the retread-process RPs and the TMC condition guide — this is the "extend the casing" chapter: when to regroove, when to rotate, when retread. Michelin advises against retreaded tyres on steer axles — flag where local rules differ.