OK, here's my full description, so be ready for a read!
1. Remove wheel from bike. Not as easy as you might think! Refer to quick release discussion in previous section.
2. Look for whatever caused your flat. (Note - if while riding you see a thorn/tack/etc. in your tire DON’T PULL IT OUT! Leave it ‘till you get home or any other good place to fix your bike other than the side of the road. If you pull the offending object out - pssss! There goes your air!) Take note of where the object is in the tire.
3. Remove tire from rim. Use your tire levers to get one bead of tire over rim flange. It’s best to remove a section of tire that’s 180 degrees from the valve stem. Pinching tire beads together all around the wheel just prior to initial removal will make this step easier. Be sure to slide tire lever under the bead only - do not catch the inner tube underneath. If you do, you may pinch another hole in your tube. Once you’ve gotten a 4-6” section of bead over the rim it will loosen up, making further removal easier. Only after you’ve gotten one bead off should you proceed to the next. After removing the tire, inflate the tube a little bit before taking it out of the tire. Listen for hiss and find spot at tire where air is leaking.
4. Remove object from tire. This is a crucial step. I know a PhD who fixed his/her flat four times only to finally realize that it wasn’t coincidence that his tube had holes in the same location, but rather that what he/she ran over was still in the tire re-flatting the tube every time. While you’ve got the tire off, go ahead and check the entire circumference of the tire. Check inside and out. You may have a piece of glass or two that hasn’t worked its way through the casing. Get any foreign objects out now.
5. Install fresh inner tube. Inflate slightly - just enough so tube takes its shape. Put it in the tire while tire is completely off rim. Locate valve stem next to tire label. This is a good habit that will make you rich and popular!
6. Install tire on rim - the hard part! And here’s the coup de gras: Don’t use any tools to reinstall the tire! “Crazy” you say? With a little practice and knowledge, you will be able to do it every time! Note tire directional arrows and orient tire correctly. Start at the valve stem (opposite from removal). Put valve stem through rim and pull one bead over rim. Next, pull second bead over. Here’s where it gets tricky - with about 3-4” to go it gets hard. Before killing yourself trying to get that last bit over, first go back to the valve stem and push the valve up into the tire a couple of times. Then pinch the tire beads together. And if the tube has a little too much air in it, let some out now - but not all. The tube should still take its shape in the tire. Now attack the last section. Many people push the bead over with their thumbs. Try this method. For me, I find rolling my palms over the bead really does the trick. Now if you can’t get the tire on, try letting a little more air out of the tube. If you’re still not having luck, take a five minute break. That may give your hands a needed rest and allow the tire to “nudge” into place. Pull last section on. Ta-Da!
7. Inflate tire. Not as simple as you might think! Before inflating, if you didn’t push the valve stem into the tire in the last step, do that now. The tube has a ring of extra thick rubber around the valve stem. This little dohicky really causes trouble - it can get stuck under the tire bead during tire installation. When you fill the tire, that little bit of tube will go “kaboom!” when under pressure. Now put about 10-20 psi in the tire. STOP! Now check the tire sidewall to be sure the tire is seated evenly on the rim all the way around. Check the line on the tire; it should be equidistant from the edge of the rim all the way around. If not, pull or push on the side of the tire until it is. Now you can inflate the tire to the desired psi level. Double check seat before installing on bike. If something starts bulging - let the air out ASAP!