No...not tire flats
There is a 5mi long approach to a rather large 2mi hill that is on my training list. On that approach I notice that it doesnt seem to be as flat as it looks. So I click over to the elevation reading on the GPS to find that I'm gaining 1ft every 30ft of pavement.
Good thing I had the GPS readout or I'd been scratching my head and peddling at the same time. Of course, when I turned around at the top and made the ride back into town it becomes more obvious when suddenly it feels like a tailwind just booted you in butt. Click up a gear and get back on the horse for the ride back to town.