The basics

When to replace it

Schwalbe, a major tyre maker, gives these signs:

• The tread is worn through: you can see the puncture-protection layer or the casing threads. Replace the tyre straight away.
• The sidewall is damaged: a cut, a hole, rubber torn away showing the casing. The sidewall often fails before the tread.
• Cracks: a few large cracks high on the sidewall come from a tyre often ridden underinflated; small cracks all over the sidewall come from age.
• You puncture often: a thinner tread protects less. Replacing it a little earlier can be worth it.

Reading the size on the sidewall

The sidewall often shows three sizes. Only one is precise: the ETRTO size, two numbers separated by a dash.

• The second number must match your rim. A 622 tyre goes on a 622 rim, nothing else. The most common: 622 ("700C" or "28-inch" wheels: road, city, gravel), 584 (27.5-inch or 650B mountain bikes), 559 (26-inch mountain bikes).
• The width must suit your rim. Park Tool advises a tyre 1.5 to 2 times as wide as the inside of the rim: a rim 25 mm wide between its walls takes a tyre of about 37 to 50 mm. Also check it clears the frame and fork.
• The inner tube must match the new width.
• Hookless rim: tubeless tyres only (marked TLE, TLR), never above 5 bar.

Steps

1. Remove the wheel and the old tyre

Same as for a puncture: wheel off, tyre fully deflated, one bead out with a tyre lever, then the tube, then the other bead. It's all in Fix a flat tyre.

2. Check the rim tape

The rim tape (the strip covering the inside of the rim) must cover every spoke hole, without overlapping the edges where the tyre sits. If it's cut, shifted or damaged, replace it: otherwise the edge of a hole punctures the tube.

3. Find the tyre's direction

Look for an arrow on the sidewall (1): it shows which way the wheel turns as you ride forwards. Not every tyre has one.

4. Fit the first bead

Put one side of the tyre onto the rim by hand, all the way round. Inflate the tube just enough to hold its shape, push the valve straight through its hole, then tuck the tube into the tyre.

5. Fit the second bead, by hand

Push the second bead into the rim with your thumbs, pressing the parts already fitted into the centre channel of the rim: that gives the slack you need for the last bit. Only use a tyre lever as a last resort, never a screwdriver or a metal lever.

A new tyre is often tighter than the old one: a little soapy water on the beads helps. Never grease or oil.

6. Centre the tyre, then inflate

Inflate gently, then look at the moulded line (2) just above the rim (3), on both sides: it must stay the same distance from the rim all the way round. If it dips or rises somewhere, deflate, work the tyre at that spot and try again. Only then inflate to the pressure you want, between the minimum and maximum written on the sidewall: see Get the right tyre pressure.

Check it's done right

• The tyre is the right way round.
• The wheel spins without a bump or "hop" as you watch it turn.
• The tube doesn't show anywhere between tyre and rim.
• The pressure holds the next day.

Common mistakes

• Buying the wrong size: trusting "28-inch" or "700 x 35" rather than the ETRTO size.
• Fitting the tyre backwards when it has an arrow.
• Pinching the tube with a tyre lever at the end.
• Inflating hard without checking it's centred.

What next

Log the change in your logbook, with the tyre's make and model: you'll know how many kilometres it lasted. Check the pressure at least once a month, ideally every week.

Sources

This guide was checked against the following documents:

• Park Tool, Tire and Tube Removal and Installation (direction, centring, soapy water, label at the valve)
• Park Tool, Tire, Wheel and Inner Tube Fit Standards (ETRTO, tyre and rim width)
• Schwalbe, wear and lifespan (in German)
• Schwalbe, size designations (in German)
• Schwalbe, mounting (in German)
• Schwalbe, tyre and rim dimensions, hookless rims (in German)

Values vary between models: your part's manual always takes precedence.