Front tyre

The front tyre is the rubber cover on the front rim. It is the only contact between the front of the bike and the road, so it controls steering and most of your braking grip.

What it does

Air pressure inside the tyre carries the load. The tread pattern clears water, and the rubber grips the road. Running the tyre under-inflated makes it flex, heat up and wear on the edges; over-inflated it wears in the centre and grips less. Rubber also ages and cracks even if the tread is good.

Signs it is worn or failing

• Slow air loss or flat: Tyre slowly loses air, Flat tyre (tubeless), Flat tyre (tube).
• Cupped or uneven wear: Tyre cupping, Tyre worn flat in the centre.
• Cracks or old rubber: Tyre is cracked or old.
• Bulge or cut: Tyre has a bulge or cut. Stop riding.
• Heavy steering or wobble: Steering feels heavy, Handlebars shake.

When to replace it

Replace when the tread reaches the wear bars (small raised blocks in the grooves, marked by a triangle or "TWI" on the sidewall), at the limit in your manual, or at the legal minimum where you ride, whichever comes first. Replace if cut, bulged, cracked deeply, or about 10 years old regardless of tread.

What to match when buying

• Size, for example 90/90-17: 90 mm wide; sidewall height 90 % of the width; "-" means bias construction (R means radial); 17 inch rim.
• Load index and speed letter, a number and a letter after the size: must be at least what the manual or the original tyre shows.
• TL (tubeless) or TT (tube type). Match your rim.
• Front only or a rotation arrow: fit it the right way round.
• Date code: the last four digits of the DOT number are week and year (2423 = week 24 of 2023). Avoid old stock.
• Use the same type and tread design front and rear if you can.

Fitting notes

• Check pressure cold, every week: Check tyre pressure. Inspect: Inspect tyres.
• Line up the tyre's balance dot with the valve.
• Fitting: Replace a tyre (workshop). Never exceed the bead seating pressure on the sidewall.
• New tyres carry a mould release coating and are slippery at first. Ride gently until it wears off.
• Do not mix bias and radial tyres on one bike. If you change tyre size, change front and rear by the same step.

Reference (K-Light 125)