Choice of spare tyre and tube in Europe for 40-559(ETRTO) or 26"X1.5
40-559 is the number to match. For tubes, the ETRTO number is a range of fitting tire sizes. For complete explanation, see http://www.sheldonbrown.com/tire-sizing.html

EDIT: This answer originally hinted that 37-590 would be correct. It isn't, 559 is the rim diameter and it must match.