29 and 700 can fit the same size. As my LBS told me when I asked what the difference was is that 700 is used for the road tires and 29 are for mountain tires, but the lines are becoming blurred since some road/comuting tires are listed as 29. The reason I asked my LDS this is my new bike has moutain bike rims (29) with 700x37 tires.