I have been asked several times about punctures. A bike is normally a very reliable machine, but sometimes things need attention.
Most things that wear, or get out of adjustment will be OK until you get back home, but the one thing that needs attention right away is a puncture.
In a group of riders there is usually someone who can fix it, but it is a good idea to know how to do it yourself.
First thing is to take the whole wheel off the bike: loosen the two nuts on the axle and pull the wheel out. Many bikes have Quick Release levers so you don't even need a spanner. If the brakes get in the way they can easily be released, either by unhooking the cable or with a special in built lever in some cases.
Look at the outside of the tyre to see if there is any obvious cause for the puncture, like a thorn, that you can remove.
You will need a couple of tyre levers to unhook one side of the tyre from the wheel. If you pinch the tyre into the middle of the wheel rim it will come off more easily.
Once the tyre is off, pull out the inner tube and take it off the wheel - you may need to unscrew a little nut that holds the valve in place. Save it for later !
To make life easier it is better to carry a spare inner tube, so that you can just swap it over. So much quicker than finding the leak and glueing a patch on it beside the road. Do this later at home in the dry and warm!
Before you fit the spare tube, feel all round the inside of the tyre for any sharp object that caused the puncture. If you find it, pick it out from the outside. If you leave it there it will almost certainly puncture a new tube as soon as you pump it up.
Tuck the new tube into the tyre all the way round as far as you can. It helps to have just a little bit of air in it which you can do with one or two strokes of the pump, but I find that I can blow enough in with my mouth.
Pop the valve through the hole in the rim of the wheel and start to ease the tyre and tube back on, pinching the edges into the middle of the rim again. The last six inches or so start to get harder to push over the rim and if this seems to be too difficult, make sure that the tyre is really squeezed into the middle all the way round.
I carry a very tiny bottle of washing up liquid or a piece of soap that I can rub on the inside of the tyre at this point if I need to lubricate it , to help it slip over the edge.
Once it is in place, put the wheel back on the bike, do the nuts up, and inflate the tyre a bit. Check that the tyre is seated all the way round then pump it up hard. Refit the brakes if you unhooked them, and the valve nut, put the tools away , and off you go!