Originally Posted by
Velo Dog
For what it's worth, I've bought only two sizes of tubes for 10 or 12 years. 26x1.5 goes in everything from 1.4 to 2.3 tires, and 700x25 fits everything from 25 (skinniest tires I allow in the house) to 700x41. No problems ever.
And in a pinch you could use the 26" tubes in a 700c tire or the 700c tube in a 26" tire - installation would just need to be a little more careful. But we've had occasion to do both when meeting other cyclists stranded without a spare tube. As mentioned before, the only real problem is fitting a Schrader valve through a Presta-sized hole.