John E

I have used full-size frame-fit pumps for years and have begun to experience stem flats only very recently, and primarily on the mountain bike. I was beginning to wonder whether my the (Presta) valve holes in my rims had developed sharp edges or had eroded to a larger diameter. Although I carry frame pumps, I use them only in emergencies, relying primarily on my trusty floor pump. My current theory is that innertube quality has plummeted in recent years, and that the reinforcement where the stem attaches to the rest of the tube is less robust than in years past. I liked the good old days with large-flanged metal valve stems, which could actually be replaced. I don't think I ever had a stem base puncture back then.