What to know about motorcycle tyres
The right size
The size is set by the motorcycle manufacturer, not by whatever is fitted now - a previous owner may have put on the wrong tyre. The correct front and rear sizes are in the owner's manual.
Pressure - check it cold
Measure the pressure before riding, while the tyres are cold. They warm up as you ride and the pressure rises, so never let air out of a warm tyre - it will be under-inflated once it cools. The correct figure comes from the motorcycle manufacturer, in the owner's manual or on a sticker on the frame; the number on the sidewall is the maximum the tyre withstands, not the recommended working pressure. Michelin advises checking at least every two weeks and before any long ride.
Age - the DOT code on the sidewall
The last four digits of the DOT code give the week and year of manufacture. Rubber ages even if the tyre is not ridden: ozone, heat and UV all degrade it, and none of that is visible from the outside. Michelin advises having a tyre inspected professionally every year from its fifth, and replacing it ten years after the manufacturing date regardless of how the tread looks.
Front and rear must share the same construction
Do not mix a radial with a bias-ply tyre without the approval of the motorcycle or tyre manufacturer - the two constructions behave differently under load and the bike's handling can change unpredictably. The size marking tells you which is which: R means a radial, as in 120/70 ZR17, while a dash means bias-ply, as in 3.00-18.
Balancing and wear patterns
The wheel is balanced every time a tyre is fitted. Uneven wear - a flat band worn across the centre, or scalloped wear at the shoulders - usually points at balance, suspension or pressure rather than at the tyre, so a new tyre will not fix the cause.
Puncture repair
Tyre manufacturers do not accept external plugs or liquid sealants as a permanent repair. Only a repair made with the tyre removed from the rim, so it can be inspected from the inside as well, counts as permanent. A repaired tyre can lose its original speed rating, so the manufacturer's maximum speed no longer guarantees safety.
When a tyre must be replaced immediately
A bulge or blister in the sidewall, exposed casing cords, a cut through the casing, or tread separation all mean the structure of the tyre is damaged. Remaining tread depth is irrelevant in that case.
