Even after years of bicycling for transportation, I have plenty yet to learn.

I got on my bike one afternoon and heard "thunk thunk thunk". I know that sound. That's the sound of a flat tire! I keep a flat kit at all times so although I'd be late to my next appointment, no big deal.

But I didn't have my bike pump with me. I probably took it out of my basket at some point and forgot to put it back. A nearby gas station had air.

I took the wheel off.

I took one bead of the tire off.

The next step is to find the leak, so that I can identify the cause of the flat. If you skip straight to putting a new tube in, you'll likely just get another flat from the thorn or nail still lodged in the tire.

I started to put a little air into the tube, so that I could feel the escaping air and find the hole.

Bicycle tubes have two types of valves, presta or schrader. Schrader are the same kind that are on car tires. My bike has presta valves. Gas station air compressors aren't equipped for presta valves, so I couldn’t put air into the tube to find the leak.

I put the tire back on, walked my bike to my last appointment, and got a ride home from there.

Once I was home, I took the wheel off.

I took one bead of the tire off.

I used my floor pump to put a little air in the tube and quickly found the hole. To my surprise, it was on the inner side of the tube, not the side adjacent to the tire. The hole had not been caused by a thorn or a nail. I looked on the rim to see what might have caused the flat.

Rims have little holes where the spokes go. After assembly, these holes are covered so that the spokes don't poke holes in the tube.

When I had gotten this wheel a few months ago, I had forgotten to put rim tape on. The little stickers covering the holes were starting to come off and one had poked a hole in my tube. There's no place in town to get rim tape, so I took the other bead of the tire off and lined the rim with electrical tape.

I put a new tube in, put the tire back on, and aired it up.

My tires, Schwalbe Marathons, are kevlar lined and have overlapping segments. (One of the original tires of this type was named Armadillo.) Because of this design, direction matters. If you put them on backwards, they don't protect against flats. These are incredibly flat-resistant tires and I rarely have a flat tire.

When I put the wheel back on the bike, I discovered that I had put the tire on backwards.

I let the air out of the new tube.

I took both beads of the tire off.

I flipped the tire around, put it back on, and aired up the tube.

That is why it takes me so long to change a tire. I end up doing it multiple times before I get it right!

The last step was to replace the spare tube I had just used--and to return my little hand pump to my bike where it ought to be.