For rim brake bikes, open the brake quick-release to give the tyre enough clearance to pass through the brake pads. For disc brake bikes, brakes don't need to be opened. Open the wheel quick-release lever (or loosen thru-axle). For the rear wheel, shift to the smallest sprocket first — this makes removing and refitting much easier as the derailleur is under least tension. Lift the chain off the small sprocket as you pull the wheel out.

Release all remaining air from the valve. On Presta valves, unscrew the locknut at the top first, then depress the pin. On Schrader, depress the pin in the centre. Insert a tyre lever under the bead about 10cm from the valve and lever it over the rim edge. Hook the lever tail onto a spoke to hold it. Insert a second lever 10–15cm away and lever that section over too. Once you have a few inches of bead unseated, you can usually run a tyre lever around the rest by hand.

Once one bead is unseated, start at the valve — push the valve through the rim from outside (Presta: unscrew the locknut fully first). Pull the tube out around the rim. You don't need to remove the tyre completely to change a tube — leave the other bead seated. This saves time and reduces the chance of missing a thorn still in the tyre.

Put a small amount of air in the removed tube and listen and feel for escaping air. If you can't find it by feel, submerge the tube in water (a puddle, bidon, or bowl) and look for bubbles. Mark the hole with a fingernail or pen. Now match the hole's position on the tube to the same position on the tyre — rotate the tyre to the 12 o'clock position relative to the valve, then check the corresponding section of tyre tread and inner wall.

Carefully run your fingertip along the inside of the tyre in the area corresponding to the hole. Feel for thorns, glass, or wire fragments. Many puncture causes are invisible to the eye but easy to feel. Remove anything you find with tweezers or a fingernail — don't push it in further. A hole in the tube with no corresponding object in the tyre means the object fell out — check the road surface area where you flatted if you can.

Roadside: swap in a fresh tube. It's faster and the join is stronger. Take the punctured tube home to patch. For patching at home, use a proper vulcanising patch kit (Rema Tip Top is the benchmark): roughen the area with the sandpaper in the kit, apply rubber cement thinly and let it go tacky (2–3 minutes — don't rush this), then press the patch on firmly and hold for 60 seconds. Self-adhesive "glueless" patches are temporary — good for roadside emergencies but not as reliable for long-term use.

Put a small amount of air in the new tube — just enough to give it shape. Push the valve through the rim hole and tuck the tube inside the tyre all the way around, making sure it's not twisted or kinked. Starting at the valve, push the unseated tyre bead back onto the rim with your thumbs. Work away from the valve in both directions. The last section near the valve is the tightest — push the valve inward to give more slack and work the bead over with your thumbs. Avoid tyre levers for refitting — they can pinch and puncture the new tube.

Before inflating fully, inflate to about 20 PSI and check all the way around both sides that the tyre bead is seated evenly on the rim — look for the moulding line on the tyre sidewall, which should be visible and even all the way around. An unevenly seated bead will balloon out and blow off the rim at pressure. Once satisfied, inflate to riding pressure. Check the Tire Pressure Calculator for your weight and tyre width if unsure.