That's normal. Think about it, the wheel would measure differently for different widths of tire, and would only be a true 26" with ONE width, which IIRC is 26x1.9". I'm guessing your wife's tires are marked 26x1.5 or thereabouts. For road use, I consider anything over 1 1/4 to be "fat." I sometimes run a 26x1 on the back of my recumbent; same rim but with the skinny tire the overall wheel only measures a bit over 24" tall.