Uneven or abnormal tyre wear

This is by far the most frequent cause of abnormal wear, and the simplest to fix. Pressure determines the shape the tire takes under load, and therefore which area bears the weight and wears. Underinflated, the tire flattens and bears mainly on the shoulders (the edges wear fast), while also overheating excessively (a risk to the carcass); overinflated, it bulges and bears mainly in the center (the center wears down and flattens, giving a "squared" profile). Incorrect pressure therefore prematurely ruins the tire while also degrading handling, grip, and braking. The check must be done cold (riding heats the air and skews the reading), with a reliable gauge, at the manufacturer's values (a sticker near the swingarm or the manual), which differ front/rear and by load. This is a basic, free job, to be done regularly (every two weeks). Correcting pressure stops further abnormal wear, but doesn't "repair" rubber already worn away: if the tire is too far gone, it will need replacing. Important: a tire that keeps losing pressure despite being correctly inflated has a leak (valve, rim, puncture) to fix. This is the first cause to check for any abnormal wear, before suspecting alignment or suspension. Regular pressure checks are the most cost-effective maintenance habit for tire life and safety.

If the rear wheel isn't perfectly in line with the front wheel, the tire (especially the rear) "drags" slightly sideways and wears diagonally, meaning more pronounced on one side of the tread than the other. The most common cause is chain adjusters set differently on each side: the two sides of the swingarm adjusted unevenly shift the wheel out of line. An impact (curb, pothole) or a bent swingarm/frame can also cause misalignment. Beyond premature tire wear, misalignment also wears the chain and sprocket faster and degrades handling (the bike may pull to one side). Diagnosis is accessible: compare the marks etched on the chain adjusters on each side of the swingarm (they should match), and if in doubt, measure the distance from a fixed point on the swingarm to the wheel axle on both sides (they should match to within about 1 mm). Adjusting the chain tensioners and retightening the axle to torque is intermediate-level; a precise alignment (laser or straightedge) by a professional is ideal, especially after an impact where the geometry also needs checking. Distinguish this from pressure-related wear (which is symmetric, center or shoulders): here, the wear is clearly asymmetric, diagonal. Correcting alignment stops this type of wear and improves both handling and drivetrain life.

Warning: suspension is a safety component, and its diagnosis is reserved for a professional (expert-only). A rear shock or fork at the end of its life (dead hydraulics, sagged spring, leaking seals) no longer controls the wheel's movement: over irregularities, the tire bounces and momentarily loses contact with the road, creating characteristic facet or scalloped wear (small, regular wave-like patterns on the tread). This "stair-step" wear is the signature of suspension that's no longer doing its damping job. Beyond tire wear, dead suspension badly degrades handling, grip, and braking, and stresses other components. This cause is rarer than pressure or alignment issues, but serious. Diagnosis (checking damping, leaks, the spring, the fork's condition) and repair (servicing or replacing the shock/fork, seals) require specialized tools and experience: leave it to a professional. Before considering this, rule out the simple causes (pressure, alignment). Distinguish it from other wear types by its very distinctive facet/wave pattern. Dead suspension shouldn't be neglected: it compromises safety, especially at high speed and on poor road surfaces, and keeps ruining tires until it's repaired.

Repair to be left to a professional.

This isn't a fault, but an explanation worth factoring in: some wear simply comes down to how you ride and the trips you take. Lots of motorway and straight-line riding wears mainly the center of the tire (which flattens into a "squared" profile); lots of winding roads wears the shoulders more; very sporty riding (hard acceleration, heavy braking, lean angle), or a bike often heavily loaded, speeds up overall wear. This is normal and inherent to use. The "fix" is to understand this wear so you can adopt a few habits that make tires last longer (checked pressure, slightly calmer riding) and, above all, to better choose your next set of tires based on your actual use — a harder, more durable sport-touring compound if you do a lot of motorway riding, a softer sport compound if you do a lot of cornering. This is a basic step, with no immediate cost. Be careful, though, not to blame "riding style" for wear that's actually caused by incorrect pressure, a misalignment fault, or dead suspension: those causes do deserve correction. Wear that's consistent with your usage, on properly inflated and maintained tires, is normal; just make sure to replace tires before they reach the wear indicator (1 mm minimum by law in France).