I am looking at the new Continental on off road tyre which is available in 17" size for the front wheel of your X. I too wanted to have two sets of wheels, 17" for road and then 18/21 for the winter and gentle off road but the X and the R front ends are totally NOT compatible, brakes and forks are not the same. Good luck!!

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(Now sold on, sob) 2011 Blue XT660X with gold wheels, was 26,500 km.
Engine mods: K&N Stage 1 filter, DNA Stage 2 filter, snorkel removed, Kev fuel mod fitted.
Plus: smoked Puig screen, Yam aluminium sump guard, Yamaha / Acerbis handguards, Givi Trekker aluminium side cases, Leo Vince X3 cans plus Kev front fork mod and Fender Xtender. Just fitted Michelin Road Pilot 3 tyres.

SOLD the XTX for a Super Ten 1200. And just bought a Raptor 700 so staying on here for some tips....