I used to have koxx forxx before they came unglued (d'oh! ) which have the mounts put on so they're +30mm anyway and I ran a 190mm disc, which was great. However, on my new Urbans the mounts are in the normal position so i had to go back down to a 160mm rotor, which doesn't hold. Sooo... basically a +30mm would let me run my old rotor again