You'll also need a bracket to space out the front calliper for the bigger disc.....or use Xmoto forks if you're using an Xmoto front wheel.
The cheapest way is to find 17" wheels that more or less fit (haven't a clue what'll work with a Xchallenge, sorry) and then make up spacers to fit.
You may want to play with gearing (sprockets) as well......oh and dropping the forks 10-15mm in the yokes to speed up the steering often pays dividends.
Andres