I also had 38cm cannondale bars-- last friday I swapped stems and the new stem required different diameter bars and they measured me at the shop by holding the bars up so it was the same as my shoulder to shoulder width and that was the size they put on the bike - 40cm - made such a difference and opened up my chest from being constricted by my hands going too much in front of me and so is a big improvement just from that 2cm wider bar--