A spare tube or a patch kit
Allen Key/Spanner (for bolt through axles)
First up, you need to stop safely. If you have a sudden flat, you’ll end up with reduced control as the tyre rolls across the rim. On the back this tends to cause a little oversteer, but on the front this can result in total loss of control. In both cases you need to try to stay in as straight a line as possible, and be very gentle with the brakes, much the same as in a car with a flat tyre. If the tyre is only slowly deflating this is less of an issue.
Once you’ve managed to safely stop, you need to remove the wheel from the bike ( If you’re replacing the front tube in a bike with a Cannondale Lefty, you can skip this part). Flip the bike upside down, and undo the quick release. If you’ve got bolt through axles you’ll need to be carrying the appropriate tools for this. If you’ve got rim brakes you’ll need to disengage these now. For V-brakes push the arms together, then flip the cable out of the slot. For other styles of rim brake, you’ll need to work out how to disengage them, but it’s normally fairly easy to work out. Disc brake users have it easy – you don’t have to worry about disengaging the brakes.
Once you’ve got the wheel off, run your hands around the tyre, pushing one side of the tyre against the other. This makes it easier to get the tyre off by getting the bead of the tyre out of the channel in the rim it normally sits in. Now put a tyre lever in to the side you’ve pushed in, roughly opposite the valve, and lever it up so that the bead swings over the rim. Depending on the rim/tyre combo you may be able to do this with your fingers or with one tyre lever, but often you’ll need two or three tyre levers to get the bead off. If you do need to use multiple levers then work around the rim in an orderly fashion. Good quality tyre levers make this easier – the large flat yellow ones made by Michelin are the duck’s guts. Cheap tyre levers can bend and break, particularly when you’re using a tight tyre/rim combination, like a 1.5″ slick on a Sun Mammoth rim! If you don’t have tyre levers be inventive – I’ve seen screwdrivers, allen keys and even table spoons used in a pinch!
Once you’ve got one side of the tyre off, pull the dead tube out. It’s often worth inspecting the tube or even inflating it to look for the holes. If it’s a pinch flat, with a hole on each side of the tube, then you’ve probably just hit a rock with not enough pressure in your tyre. If it’s a single hole it’s worth inspecting the inside of the tyre for any sharp objects which could puncture your spare tube. If you’re getting a lot of pinch flats try increasing the pressure in your tyres, or riding a little nicer. If all else fails consider getting a premium tube like the Hutchinson greens.
If you’ve got a spare tube, you can use it now. If you haven’t (you’re a bit of a dill, aren’t you? ), then you’ll have to use a patch kit. Use the sandpaper or metal rasp to rough up and area about twice the size of a patch, centred on the hole. This is to get rid of the release compound used in making the tube, so that the glue sticks to it. Since it’s bad for the glue to not stick, really rough up the tube. Once you’ve done that, smear a very thin layer of glue around the roughed up area.
Basically you want to get an even covering that is as thin as you can get while not leaving any dry patches. Leave for a few seconds until the glue gets a little bit tacky, and pull the foil backing off the patch while you’re waiting. Push the patch on nice and smoothly, then hold it there firmly for at least 30 seconds. Ideally you should patch a tube and leave it 24 hours before using, but if it’s all you’ve got you should be OK to use it after a few minutes.
Put just enough air into the tube to make it hold its shape. Now put the valve through the hole in the rim and push the tube into the tyre the whole way around the rim. Starting at the valve stem, push the loose bead of the tyre back into the rim, moving around the rim in both directions. Again you may or may not need tyre levers to get the last bit of the bead seated. Make sure you don’t catch the tube between the rim and bead while doing this – that’s one of the reasons for partially inflating the tube before you put it in the tyre.
Once you’ve got the tyre back on, pump it back up to your desired pressure. Put the wheel back into the dropouts. If you’re using rim brakes it can help to use your foot or a friend to hold the brakes on, which self centres the rim. Tighten the quick release or axle, and double check the brakes run freely. If they don’t, loosen the quick release and adjust the angle of the wheel – you can normally move the rim through about 3mm each way, so you should be able to get your wheel running freely, provided it’s relatively true.
Flick your bike upside down, pick up any patch bits, old tubes, or other trash, give your bike a final check, and you should be right to go!