Originally Posted by pwdeegan

clarification: the same tires won't necessarily fit the same frame. e.g., a 47cm frame with 700c wheels (and therefore 700c tires) will not be able to use the tires from a 62cm frame that uses 26" wheels. The wheel size (and therefore tires size) of 26" or 700c refers to the wheel's diameter, and different wheel sizes are not interchangeable even if the frame sizes are identical.

so just be sure that if you want to mix-and-match tires that your wheel sizes are the same. for more information, see: http://sheldonbrown.com/tire-sizing.html