Dont forget that whatever you choose with tyre size or if you change the gearing, or just general speedo calibration, it can all be done very easy with a speedo healer, fantastic piece of kit.
http://www.bikersdiscountstore.co.uk...aler-pl-19.php
Why not just get a new EXCEL rim laced up with stainless spokes, unless you are doing enduros , there is a good selection of tyres for you to use, MITAS or ARMY SPECIALS all in 17 inch and 21 inch
v-tec