If you get a puncture on the way to work, it's quicker to replace the innertube than to fix the hole. You can do the repair later – at home. These instructions assume your bike has derailleur gearing. If it doesn't, practise removing and refitting the rear wheel or see the Prevention, not cure box.
To get even a semi-inflated tyre past a rim brake's pads, you may need to undo the brake. Sidepull brakes have a lever on the calliper to open it out. With V-brakes, the J-shaped 'noodle' unhooks from the yoke. With cantilever brakes, the cable unhooks from one brake arm. Disc brakes can be left alone. For a back wheel puncture, click up the gears until the chain is on the smallest rear sprocket, turning the cranks by hand. Then turn the bike upside down.
2. Remove wheel
Front wheel: Note which side the quick-release lever is on. Undo it. You'll need to partly unscrew the knurled nut on the opposite side as the fork has 'lips' to stop the wheel falling out accidentally. Rear wheel: Undo the lever. Pull the derailleur back out of the way and lift the wheel up and out.
3. Remove innertube
Insert one tyre lever under the edge of the tyre (the bead) and lever it off the rim. Hold or secure this lever while you insert the second lever 10-15cm away on the same side. Lever up the tyre, then run the second lever around the rim, lifting the tyre bead completely away on one side. Remove the innertube's valve cap and locking ring, if any, then pull out the tube.
4. Locate puncture
Unless the source of the puncture is obvious, inflate the innertube. Feed it past your ear, listening for escaping air. Hold the innertube against the wheel, matching valve with valve hole. If you didn't flip the innertube, the hole you've found will line up with what caused it. If you don't find anything, run your fingers carefully around the inside the whole of the tyre. Remove any sharp object(s).
5. Fit new tyre/refit tyre
Pump a little air into the new tube to give it some shape. Fit the valve in the rim, then feed the rest of the tube into the tyre. Now tuck the tyre bead back into the rim. Starting opposite the valve, work both hands around the tyre in different directions, tucking the bead in with your thumbs as you go. Most of the tyre will soon be fitted, with a tight line running from 'ten to two'.
6. Fit last section of tyre
Avoid using levers, which may pinch the innertube. First let the air out of the innertube. Then, while one hand holds the tight section, work the other around the fitted section, pressing the sides together and forcing the tyre down into the central well of the rim. This will win you some slack so you can push more of the tight section over the rim. Repeat as necessary. Eventually you'll be able to lever it on with your thumbs or roll it into place with your hands.
7. Inflate tyre
Press the valve up into the valve hole to check the innertube is not trapped under the tyre bead. Pump the tyre up a little to give it some shape. Spin the wheel to ensure the tyre is mounted evenly. If not, you'll need need to push and pull the tyre from side to side until it fits neatly. Sometimes the tyre pops into place in the rim only when it's fully inflated. Do that next.
8. Refit wheel
Front wheel: Make sure the quick-release lever is open and the wheel is the same way around as before. Fit the axle into the dropouts – and, if need be, the disc rotor into its calliper. Push down to seat the wheel. Tighten the axle's knurled nut so that the lever starts to snug tight when it's half closed. Closing it fully should require firm pressure.
Rear wheel: Pull the derailleur back, align the smallest sprocket with the 'top' run of chain (i.e. nearest the ground, with the bike upside down) and guide the axle into the dropouts. Press it home, then do up the quick- release securely.
Put the bike the right way up, reconnect the brake you undid, then rotate the cranks by hand to check the chain is running as it should. Done.
PREVENTION, NOT CURE
Firmer tyres Firmer tyres puncture less often. Keep your bike's inflated to the pressure that's stamped on the sidewalls using a floor pump (track pump).
Thorny issue A thorn that's stuck in the tyre usually plugs the hole, so air seeps out slowly. If it's practical, leave it in, top up the tyre with air, and continue.
Tyre sealant Puncture sealants like Slime coat innertubes with a liquid that plugs and hardens to fix smaller holes. Some air escapes, so it's worth carrying a pump.
Puncture resistant tyres The toughest tyres are called 'something' Plus, such as Schwalbe Marathon Plus or Contintental Touring Plus. They're harder to fit but but are near impregnable.
Solid tyres Avoid. Solid tyres are slow and uncomfortable, and make your bike handle poorly. Get puncture resistant tyres instead.
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