Originally Posted by
IANative
The narrower tires would be to improve the bike's handling in the corners and turns of the trails- the 700x45 tires that come stock on the Crosstrail could definitely be improved upon. Something in the 35-40 width, maybe a front tire slightly narrower than the rear. Not entirely sure yet; more research required.
in most situations, but especially in gravel/ dirt, you want a wider tire on the front for more traction in the turns. you'll probably want to look at cyclocross tires if you want to improve your handling in gravel/ dirt and you're dead set on using skinnier tires. you can find them from 28 all the way up to 40. most of the 700 x 45 size tires are designed for hybrids that see mostly road use, not for going fast off road. you could always put a 29er tire on the front if you really want more front end grip.