It is not a flat. A flat is honest. A flat lies down in the driveway and refuses. This is a slow leak, which is a tire that agrees to the ride and then quietly changes its mind partway through.
So there is a ritual now, the wrong kind, the kind you resent. Pump before every trip. Thumb the valve first, a wet thumb, to feel for the hiss I keep deciding I imagine. Forty strokes, until the tire goes from soft to firm and the pump handle stops sinking easy. The patch is under there somewhere, a patch I put on myself, and it half-holds. It buys me an hour. Maybe two on a cool day. The heat lets the air out faster, or I think it does, and I have stopped trusting anything I think about this tire.
The real ride is a race against a slow surrender. I go out firm and I come back on my judgment. Halfway to town the tire starts reading the road more honestly, every pebble arriving up through the rim, the bike sitting down a little on that corner. That is the tell. That is when I turn for home whether I am done or not. You learn to gauge distance in remaining air.
I have gotten good at cutting it close, which is not a skill anyone should want. Once I came in on the rim for the last block, the tire flat gone, the bike loud and wallowing and slow, and I made it, which taught me nothing.
Tonight I pumped it up and leaned the pump on the wall and by the time I had hung my jacket the tire had already given back the first of it, soft again at the top of the curve where my thumb went looking.