1 Detach the wheel
The front wheel is easy: release the brake, open the quick-release lever, loosen the nut and pull the wheel from the fork dropouts. The back wheel is harder. Shift the gears to the smallest cog to make reinstallation easier. If you’re on your bike when you notice the flat, shift as you slow down. Loosen the brakes and nut, pull down on the derailleur (as pictured) and slide the wheel out. Lie your bike, chain-side up, on its side.
2 Take the tyre off the wheel
If you use tyre levers, jam the flat end of the lever between the wheel rim and tyre, and scoop it under the tyre edge. Then push down on the lever and hook the other end of it to a spoke. Insert another lever less than five centimetres away from the anchored one, and repeat, which should loosen the edge
of the tyre and allow you to unseat it all the way round. When you have done so, remove the inner tube.
3 Inspect the tyre
Using your fingers and eyes, check the tyre inside and out for whatever caused the puncture. Take your time and remove all suspicious matter. Back-to-back flats are bad news in training or a race.
4 Install the new tube
Twist open the valve of the new inner tube and pump in a little air, which makes it easier to stuff into
the tyre. Thread the valve into the hole in the wheel rim; this will serve as an anchor as you push the rest of the tube into the tyre.
5 Ease the tyre back onto the rim
The key to preventing part of the tyre slipping off just where you put it on is to start at the valve and stretch the tyre with both hands, moving way from the valve. Use a lever for the last little bit if you need to, but be very careful not to pinch any protruding bits of tube. To check it, squeeze both sides of the tyre as you work around the wheel, making sure the inner tube is enclosed by the tyre; then pump it up.
6 Reattach the wheel
On the front: fit the fork onto the skewer (the quick-release lever goes on the left side of the bike) and tighten the nut, then flip the lever closed and tighten the brakes. For the rear wheel, hold the bike's back half, then focus on getting it positioned so that the cogs are anywhere in between the chain. Then set the bike down and tweak until the frame and wheel are properly married up - this can take a minute or two. Tighten the nut, quick-release lever and break, and you're ready to go.
On the road
The single best way to avoid a flat is to inspect your tyres regularly for cuts (if you can push your fingernail into a cut, it's time for a new tyre) and to pump the tubes to 100 or 110 psi before every ride to minimise the chances of a pinch flat. These are often caused when an under-inflated tube is pinched between the rim and a sharp, hard object.
You're less likely to get a flat tyre if you invest in puncture-proof tyres, such as Specialized Armadillos, which feature a protective Kevlar barrier.
By removing and refitting your tyres at home, not only will you feel fully prepared for whatever you may meet on the road, you'll also loosen the tyres to make repairing a flat tyre easier the next time round. Tyres stretch with time, which makes them a little easier to manipulate.
Carry everything you need to repair a flat tyre. This means a spare inner tube, two tyre levers, a pump and a puncture-repair kit.
Pump it up
Buy the biggest pump that will fit on your bike. The bigger the pump, the more air it pushes per stroke, and the quicker you'll fix a flat.