I've got 27x1¼" Conti Gatorsksins on the Skinny Bike, and 26x2" CST Squals on the Indestructabike. One flat each, both snakebite pinch-flats caused by underinflation. I no longer go by feel, and use an actual bike tire pressure gauge once a week. I'm 320lbs, and I live in Providence, RI where they seem to use broken beer bottles instead of sand on the streets when it snows.