About wider tires

Lots of new people around here ask about putting those cool, phat tires on their 250 that they see on bigger bikes and on TV. This is a really bad idea, and if you can't live with what we just said you'll be better off getting the 600 supersport that you really want.

The EX250 rear rim ('86-07) is only 2.5" wide. Anything wider than 130mm gets pinched in the rim and really compromises the handling that people think they're going to get with a wider tire. Read here for information on this subject.
And here. And here.