No one seems to have the right size in stock. I did find this online tire calculator:
http://www.discounttire.com/dtcs/infoTireMath.dosIt helps to understand the differences, but I'm not sure which size I can safely run.
BikeBandit has the K555 in stock for $106.56 to your door, but I think I can find a slightly larger tire cheaper. The 140/80-15 size doesn't seem to be very popular.
What sizes have you guys ran in the past?