Approaching mile 16 of my ride, which was supposed to be a nearly 19 mile ride out before turning back, the rear tire of my trusty steel steed went pillowy soft. Not flat, mind you, but so soft that it was all squirrely.
Nothing that five minutes with some tire levers and a mini pump could not fix. That is when I was witness to the horror.
Inside my bag was not a replacement 700x30C tube, but a 26×1.25 tube. I tried pumping up the tire thinking that the presta valve might have come loose and leaked out some air. It would not hold any more than approximately 25-30 PSI of pressure.
There is nothing quite so nerve racking as babying a rear tire with almost no pressure across almost six miles of fresh gravel and ten miles of pavement. Turns were a real treat as my rear tire would wander and squirm at the slightest provocation.
The moral of the story is check your repair supplies more than once a season. I obviously had not changed over my tubes from my commuting rig to my cyclocross ride. Now you know and knowing is half the battle.