This is going to be a quick-and-easy blog post. Most of you have probably done this before, but if you’re still taking your bike into the shop when you have a flat, today’s the day you become just a tad more self-sufficient.
Getting the old tube out
On a mountain bike, you might not even need tire irons for this. Just let any remaining air out of the tube, pull the tire sideways away from the rim, and the bead will probably unseat itself. Slide the bead off around the full circumference of the tire (remember, you don’t need to take both sides of the bead off the rim) and pull the tube out.
On a road bike, you might not be able to do this by hand, so you’ll need tire levers. Thread the wedge-shaped end of the tire lever under the bead, pry it off the rim, and hook the other end of the lever on the spokes (if your levers have hooks) to hold them in place. Insert the other lever in the gap and slide the bead off the rim.
Checking the tire
This is an important step, and one that’ll save you a lot of money on tubes. It’s often the case that whatever gave you the flat tire in the first place — thorn, glass, staple, whatever it might have been — is still in the tire. If you put a new tube in, that little sharp thing will poke a new hole in the new tube and you’ll still have a flat tire. Take a piece of tissue, or a sock if you’re on the trail and don’t have a tissue with you, and run it around the inside of the empty tire to see if it catches on anything.
Putting in the new tube
You’ll probably find it easier to put the new tube in the tire if it has a little bit of air in it, so give it a pump or two so it can hold its shape. Feed the tube into the tire, then start to seat the bead of the tire on the rim. This will start easy and then get more difficult as the bead gets tighter and you work your way around the rim, and that’s where the pitfalls usually come in. On a mountain bike tire, seating the bead can often be done by hand without much trouble, since beads are looser and rims are wider. On a road bike, it can be a real pain.
Use the levers to gradually seat the bead on the tire, being very careful not to pinch the tube between the bead and the rim. Here’s where you’re likely to have one of two problems: you’ll either pinch the tube and create a hole in it, or you’ll miss a spot when seating the bead. When that happens, you won’t notice until you get pressure into the tube, at which point it’ll explode very loudly out of the gap in the bead. It won’t hurt you, but it’ll make your ears ring and scare the pants off you, so you want to avoid it.
In order to avoid those two problems, you’re going to re-seat the bead of the tire slowly and carefully, making sure to push the tube into the tire before you follow it with the bead. Once the whole bead is seated, work your hands around the entire circumference of the tire, pinching it together to make sure that the bead is fully seated on the inside of the rim and that there’s no tube pinched between the bead and rim.
Now you’re ready to inflate. First, inflate to 10-20 psi. Repeat the whole pinching process, pushing the bead inward to make sure it’s seated properly. Deflate the tube. This time, inflate it to maybe 30 psi. Repeat. By gradually inflating, pinching, and deflating, you force the tube to adjust itself and straighten itself out, thus avoiding the blowouts that ruin tubes and frighten your pets. For a mountain bike, this’ll only take one or two intermediate inflations. For road bikes, it might be 3-4. But once you blow out a tube — and believe us, eventually you’ll blow out a tube — you’ll see why this is worth it. Once the tube is fully reinflated, you’re ready to go. Enjoy the ride!