Uneven or abnormal tyre wear

Warning: tires are the bike's only contact with the road — abnormal wear affects safety (grip, handling, braking) and deserves to be understood and corrected. You notice a tire wearing unevenly: a smooth center with the shoulders still fresh (or the reverse), diagonal wear (one side more than the other), or facet/scalloped wear (a sawtooth pattern). The wear pattern is an excellent clue to the cause. Center wear most often comes from overinflation (or lots of motorway riding); shoulder wear from underinflation (or lots of cornering) — in both cases, pressure is the first thing to check, and it's free. Diagonal (asymmetric) wear points to a wheel alignment fault (chain adjusters set unevenly, an impact) or sometimes a chassis problem. Facet/scalloped wear often signals tired suspension (a dead shock or fork) letting the tire bounce. Finally, riding style and the type of trips explain part of the wear (without being a fault). The distinction comes from where the wear is located and from checks (pressure, chain adjuster marks). Urgency threshold: abnormal wear isn't an immediate danger as long as the tire stays within tolerance, but it reduces grip and often reveals an underlying fault (pressure, alignment, suspension) that needs fixing — and a tire worn to the indicator must be replaced without delay. Fixing the cause early saves the next tire from being ruined too.