carefull with the wishfull thinking that you could put any bicycle into the overhead
http://articles.chicagotribune.com/2...-personal-item

I have problems putting a soft half full backpack into the square box, provided in every airport to check the size.
here are the sizes for peeps who dont want to read the full article above
14-by-22 inches and 9 inches deep, including handles, wheels and legs.

Much luck :-)