I have measured my one larger carry on and if it is totally packed and I mean stuffed it is just over the limit at 51 and a half inches measured as UPS does. I'm in compliance and I resent not having a spot for my bag because some recto cranial inversion brings on a bag that while it fits it is nearly 3 to 4 times the legal size.
I hear ya' Piney. I carry an ancient Samsonite Silhouette hardshell that is well within the carryon limits of my preferred airline (AA) plus a small computer/personal item. And nothing frosts me more than some novice airline employee or fellow traveler who says "hey, that carryon is too big and you're gonna need to check it."
Screw That! On many airplanes, the Samsonite goes in the overhead bin wheels first (most bins can accomodate three similar bags this way) and the computer goes under the seat in front of me. I'm usually in F (what with AA's complimentary F upgrades for EXPs), so there's almost always lots of bin space and plenty of room in front for the computer bag.
But what happens if I'm not one of the first to board the airplane? Overhead bin pigs stuff their carryon, their personal item, their duty free grocery bag, their overcoats and their assorted other crap in the bins - quickly filling them. Leaving me with precious little room for my one rollaboard carryon. :angry: