On looking at Sheldon Brown´s tyre width calculator (http://www.sheldonbrown.com/tire-sizing.html) it appears that the correct width tyre for my Mavic 559 x 17 rims is a tyre with a width of between 25 and 37 mm. I took my bike in and asked my LBS for some light weight MTB tyres and they gave me some 54-559 Schwalbe Black Jack light folding tyres. Obviously the width of these tyres (54mm) is much much higher than recommended by Sheldon. These tyres should be on super wide rims (like Snowcats) according to Sheldons table
So what has happened? have they sold me the wrong tyres? should I go back there and kick their asses?