This got me curious, I went and measured my mtn bike, its at 290 with 26x1.5 Schwalbe.
My Tricross, the cross-bike like Dougs Volpe, or should I say mine is a faux cross bike, its never seen tires other than 28 slicks, its bb is at 275ish

the diff btwn the mtn bike and the Tricross is most likely a certain amount due to the 1.5 tires being taller than the 28 Gatorskins.

My wifes tiny XS Giant Avail road bike is 270ish.

I was too lazy to take a kids bike, and old tires off the hooks to get to my hanging old touring bike, so dont know what it is.

Interesting, not a big difference between them, even though the mtn bike is a somewhat large size.