Going on modern measurements I think I understand as follows:- rims - shown as xxx-xx where xxx equals rim diameter and xx equals interior rim width. ie 622-15 is a 700c mavic open pro road rim and 559-19 is a mavic XM719 mountain bike rim. All these measurements are in mm. tyres - shown as xx-xxx where xx is the tyre width and xxx the rim diameter it will fit on to. So 50-622 is a Schwalbe Big Apple for a road rim and 50-559 is the same for a MTB rim, again all in mm. But what works with what? I get that you need the diameters to match, so tyre and rim should both be 622 or 559 etc. But what about what tyre width fits on what rim width? to date I've gone by Sheldons little table but am getting confused by what is on manufacturers sites:- Mavic A719 722-19 rim accepts 28 to 47mm tyres, Mavic 559-19 rim accepts 1.5 to 2.3 inch tyres. Why they switch to inches from mm I don't know and why one 19mm wide rim takes 28 to 47 and another 38 to 60mm I don't know. There are even bigger discrepancies with other rims, I've seen a 559-17 quoted as taking tyres 1 to 2.1 inches or 26 to 53mm tyres. Can anyone make this clearer for me? specifically I'm thinking of running some big tyres/29ers and am trying to understand what I can put on what 700c rim.